All right, can you guys hear me? Okay awesome.
Welcome everyone. Thank you for braving the cloudy weather. I know that's not always great for turnout, but it's still a good turnout
this is our final event of the of the year and
But we have a whole host of additional events coming up for the next six months
the first of which
There was a flyer outside
For there's a lunar eclipse next month
That basically happens at the time that we would normally be having the lecture, unfortunately
It's a Sunday instead of a Friday, but we're still going to do it anyway
so our next event is there's gonna be a lecture given by a postdoc here who works on LIGO on
gravitational wave astronomy and then afterwards we'll have will go out and view the
lunar eclipse that's going on with our normal stargazing out on the field as well as just like viewing the Eclipse because it's
Raise your hand if you've seen a lunar eclipse before.
So the moon turns red and all of that
So it'll be fun.
But we'll also look at other objects in the sky like the Orion Nebula and the Pleiades and the Andromeda
Galaxy and so on and so forth, so it should be good and if it clears up tonight, we'll probably do that
But I don't anticipate it clearing up tonight, unfortunately
And we also have
Astronomy on tap events which are in addition to our monthly lecture series that you're at now
We have these astronomy on tap events that take place in a bar in Old Town Pasadena where we have informal talks given by
astronomers here at Caltech or the Carnegie observatories or JPL or various other institutions and you can have beers and
Talk with astronomers and hear about astronomy in a less formal
Environment and it's totally free. So I encourage you guys to go to that our next one of those is January 28th
But the schedule will be up online shortly. I've assembled the dates but haven't gotten all the speakers
What else oh, so just as a schedule of what we're going to do tonight
I'll introduce our speaker in a couple minutes
And then and then he'll give the give a talk for about 30 minutes followed by rather than having the stargazing outside
We'll set up this table in here and there will be a number of different
Graduate students and postdocs to answer any questions you might have about astronomy or physics or space
And that'll go until 9 o'clock and you don't have to stick around but you're encouraged to stick around if you have some burning
question about the cosmos that you must get an answer to so and
All of our events are recorded and they're on our website you can you can you can go there
We're also uploading them to to YouTube with
subtitles and translations so that other people who aren't able to attend can watch them and and find out about all of our our
science education
So I think that's it in terms of announcements. So to introduce our speaker, it's me, so
I'm Dr. Cameron Hummels. I'm a postdoctoral researcher here and in addition to my science
Which I'll talk a little bit about today. I run the public education events here
So I run these this lecture series and the astronomy on tap and we do a few other
educational events, but
Let's see. How do I introduce people? I
Did my PhD at Columbia University and then did a postdoc at
University of Arizona in Tucson, and I've been here for three years and I primarily do galaxy evolution studies.
so and I'm gonna talk about that so
Please welcome me!
Okay, so
Yeah
Galaxy evolution and formation. This is a movie--this isn't real.
This is a simulation that a friend and colleague of mine named Nathan Goldbaum put together on a supercomputer
that was run out of Illinois, of an evolution of a Milky-Way-like galaxy
I'll talk a little bit more about what's going on in this later on but first, let's start with a very basic question
What do we see when we look up in the sky?
Yes tonight. Absolutely. This is pretty accurate rendition of what we see when we look up in the sky
Or if it's a if it's a nice day from Los Angeles
We can't see a whole lot just because of the light pollution in big cities
so when there's a lot of light some of that light goes up, it scatters off of particulate and
Molecules in the upper atmosphere and reflects back down and it blocks it
It increases the surface brightness of the sky so we can't see the faint objects back behind it
But let's pretend that we're not on the Hollywood sign and that we're looking out
Let's say 300 years ago before there was a lot of electric light sources and and you could actually see the night sky
So here's Badwater Basin and Death Valley when you look up in the night sky
For the first part of this talk it's going to be historical
Like what do we what was the state of astronomy 300 years ago 200 years ago
So when you look up in the sky, what do you see?
Stars. Yes, very good. People see stars
What else do you see?
Planets. I heard planets. Good. Okay, so
Planets tend to be, at least in our solar system, the inner planets tend to be much brighter.
Oftentimes you might confuse them with the star
In fact Venus is oftentimes referred to as the evening star or the morning star.
It just looks like a very bright star but it doesn't twinkle because it's closer and and so on and so forth.
But the stars because they're the stars--the planets because they're all in our solar system, which is a plane
And we also are in that solar system. We see the other planets trace out a path like a line on the sky
Which is called the ecliptic
And so you see these three planets along that ecliptic the moon also follows it but I'm not talking about the planets.
So let's move on. So what else do we see? We see the Milky Way.
Everybody raise your hand if you've seen the Milky Way. Oh
Wow, that's great. Okay, good. I'm glad to hear that. Um, if you haven't you're missing out, you should go see the Milky Way
Preferably at a nice dark site like Joshua Tree, which is only you know an hour or two away from here or Death Valley
So people have been looking at the Milky Way
For thousands of years and it's been known for quite some time that the Milky Way
You know when you see it for the first time it may not look this spectacular
but this is essentially a composite image of it across the sky and so it it
It's a big band of kind of milky light hence its name
But it's been known for several hundred years that it was actually composed of individual stars. It's not just like an extended kind of cloud
Each of each region where it's glowing is actually composed of individual stars, which you can see if you look at it through a telescope
so yeah from
250 years ago William Herschel, a famous astronomer at the time, mapped this out by looking through his telescope
He didn't have a camera. So he was just drawing illustrations of it
and
Our understanding of the of the Milky Way is that it's primarily a disc like structure
with kind of a bulge in the center kind of like this and
Our solar system is about 50% of the way out in that now. This is a modern-day image from the Gaia mission
that really
Showcases it but even a couple of hundred years ago people understood this. This was actually proposed by the philosopher Immanuel Kant
which is pretty awesome that he just like deduced that and figured it out, but
so
So it's been known for a long time
and and in fact, we thought of the entirety of the universe a couple of hundred years ago or
Even a hundred years ago was composed of our own Milky Way. There was nothing really beyond the Milky Way
That was that was the universe
So what else do we see? Wouldn't we look up in the night sky? We see comets, right? Comets are icy
objects from the outer parts of the solar system which on their way into the inner solar system start to heat up and start to
Melt and evaporate that ice off in these tails that are directed back away from a from the Sun
And in fact a couple hundred years ago, you could get pretty famous by being the first person to discover a comet
In fact, not even a couple hundred years ago. You can still be famous
If you're the first person to identify a comet then you get a name it which is pretty cool, right?
but when you first discover a comet it's not usually this bright or everyone would see it in the sky and say
That's my comet. I'm calling it after, you know, Cameron or John or Jill and so
This gentleman named Charles Messier, a Frenchman.  He essentially looked to identify comets--
A comet Discoverer. But when you first see a comet when it hasn't yet been identified
It's only a faint kind of extended smudge on the sky
It's very hard to make out but there are also other things that are faint
Extended smudges on the sky that aren't comets at all. Feel free to come in
There's still some room in this vicinity or are you free to hang out back there too, and there's room on the other side
So there are a number of other things that weren't comets that were faint extended smudges on the sky
And he didn't want to confuse those with the actual comets
So he identified a bunch of them about a hundred or so objects
And it just so turns out that these objects are actually amongst the most beautiful objects that you can view easily with telescopes
So this is just a smattering of them. They're called the Messier objects
Of course
that was the thing that he got famous for not naming the comets but naming the things that weren't comets.
You can see a number of different things. You can see kind of clusters of stars here. You can see
Kind of cloudy cloud like structures and and and so on and so forth. So as
I said that so this is this is the Pleiades cluster. It's a cluster of stars. This was one of the objects
This is Messier object 45 and we would be looking at this tonight if it weren't cloudy, unfortunately
but you also find
Other objects like this
So these are referred to as nebulae which just means cloud in Latin and it's it's like a big cloud
This is in fact a cloud that's expanding off the surface of a star. It's called a planetary nebula
It wasn't really understood that that was what was going on when it was first discovered
but in addition to these kind of cloud like things and obviously star like things there were also
these things which were called spiral nebulae and
This was the great Andromeda nebula and and you can see that there's it's it kind of looks cloudy
But it's also kind of spirally and really the question is what's the nature of these things?
are they are they in fact small and and really close and
Basically associated with a star or handful of stars or these in fact like our own Milky Way
They were referred to as are these Island universes like our own Milky Way galaxy is and it wasn't really understood
What the nature of these things were and in fact it it it eluded people for quite some time. So
In 1920, you know only a hundred years ago. We still didn't know what the heck these things were
we we essentially there was something called the great debate where the the leading proponents of the two theories got together and and
argued about based on the scientific evidence what they thought these things were were they small objects like stars or
Clouds around stars and really nearby or were they much like our own Milky Way and very very distant objects
But very very large much larger than we thought things could be because remember we think the entire universe is basically our own Milky Way
at that time
but the real way to
Check is to determine the distance to these objects if they're nearby then they're small and if they're far away, then they're very large
So typically the way we determine distances in astronomy is much like we determine distances with our eyes
And that is to say using something called the parallax method. So I want everybody to I'm gonna conduct an experiment
So everybody please raise your hand and put an index finger index finger not middle finger. Unless you're really upset with me and
Then I want you to alternate one eye open and then switch which eye is open and kind of wink wink wink wink
Between the two eyes and what you'll see is your your index finger will appear to change its position relative
to the background relative to I guess me or this screen you'll see it kind of jump back and forth and
that's essentially how we as humans or as most mammals and reptiles are able to
Identify how close you know depth perception, right? Because you can see how much something moves relative to its background because we have two
cameras, essentially that we're looking at and
This is done for astronomers as well. So the earth is orbiting around the Sun
so when we look at a nearby
Star and we image it at July and then wait six months until the Earth is at a different position in its orbit
And we image that same star its position appears to change
Relative to the background stars much like our index finger
Appeared to change its position relative to the background and so you can do this to identify
That that gives you with a little bit of trigonometry
It gives you the the distance away that that object actually is from us, which is great
Right, but the problem is that doesn't work very well the farther and farther
The object is so for instance
If you do your camera one and camera two thing with my index finger this far away
You probably don't see it move that much relative to the background as you did when it was really close to your face
Because you it only it only shifts very very small amounts of angular sanghya ler distance
And this was the problem when you were trying to measure distant objects with us with them parallax. You just can't do it very well
Fortunately
There was a an astronomer at the Harvard Observatory named Henrietta Leavitt who was able to identify
another method for determining distance around this period she
basically identified that certain types of stars called variable stars would pulsate and
when they would pulsate they would get brighter for a period and then
Fainter for a period on the order of days or weeks
and
there appeared to be a relationship between the pulsation period how long it took to pulse and how
Intrinsically bright That star was essentially giving us
like it told us that this was like a 100 watt light bulb right and if you know how
Intrinsically bright a light bulb is and how bright it appears to your face. You can tell how far away it is
so essentially this was a method for determining how far away stars were just by you measure their pulsation rate and you know,
Then you know how intrinsically bright it is. And then you measure how
Apparently bright it is and that gives you the distance
so this was a great method and
there was a
Astronomer who was here in Pasadena
Named Edwin Hubble who employed this method so Edwin Hubble must have you've probably heard of him?
Because of the telescope and so on and so forth
He did much of his work at the Carnegie observatories which are like two miles from here
And they're still groundbreaking research being done there today by astronomers from around the world
And he did it on the Mount Wilson telescope which of course is right up the hill like six miles from here
And for a long period of time in the early part of the 20th century, that was the largest telescope in the world
so there's a significant piece of history and
scientific research that that's been here a part of the Pasadena community for a long period
He's almost always shown smoking a pipe. I don't know why I guess he was always smoking a pipe
But what he did is he spent a lot of time on that telescope observing
objects like the
Andromeda spiral nebula to determine is it composed of stars or is it composed of like is it just a cloud?
Surrounding a couple of stars and what he determined this is one of his images. He's holding it here is that not only is
Is the cloud like structure of this nebula actually composed of many many small stars
distant stars much like our Milky Way is but
one of them he identified as a variable star and he could figure out how far away then that this system was from us and
He deduced that it was two-and-a-half million light years away
and at that point we thought the Milky Way was on the order of I mean we still do think that the Milky Way is
On the order of like a hundred thousand light years. So it's like 25 times farther away, which is crazy right everyone basically
Everyone freaked out because it meant that the universe was much larger than we had thought by a significant amount
So it really settled the debate and it said that these
Distant spiral nebulae these spiral nebulae were actually these very large very distant systems much like our own Milky Way
and
So here's a modern-day image
We can know a lot we no longer refer to these as the Andromeda nebula or spiral nebulae they're spiral galaxies
Because they're much like our own Milky Way galaxy
This is a beautiful image
So this is what we think of it
And like I said, here's our Milky Way
Here's the solar system about halfway out in the disk of the Milky Way and what this essentially did, is it increased
The size of the universe what we thought by about a hundred thousand. So the universe from our perspective...
Nothing real took place in the universe that day, but
Basically, we realized that it was actually about a hundred thousand times larger than we had thought up until that point which blows my mind
Not only did we realize that these distant objects were were were were large and very far away
But they were traveling away from us. So Edwin Hubble's most notable discovery is probably
That these objects were traveling away and the farther the the farther of the galaxy was from us
The faster its traveling away from us
Which is plotted very nicely here where you have the distance of a galaxy and you have the speed at which it's traveling away from
Us and you can see all these points and so the farther something is away the faster its traveling away from us
Which sounds kind of crazy initially right? Are we at the center of the universe and everything's just traveling away from us?
What he was able to deduce was that in fact, the universe was expanding. Yes. He's awesome
The universe was expanding outward and so it wasn't so much that we were sitting and everything is traveling away from us
but that space itself is expanding and so we're traveling away from
from from each other and every one appears to be at the center of their own space and everything's traveling away and
That's why
That's why you get a Space Telescope named after you it's what you do major discoveries like this about the nature of the universe
So very quickly so far
There's a lot of stuff in the sky including these smudges that we used to refer to as nebulae but we now call
galaxies
These galaxies the universe is extremely large and there are many galaxies within it
The universe is actually expanding even more and getting to an even larger size and Edwin Hubble's really a badass
Okay, so this is our nearest galactic neighbor called the andromeda galaxy again something we'd see tonight if we
had clear skies
this is the version that's on almost every
macintosh desktop
They've done some
Photoshopping to it to room to make it a little prettier, even though it's actually really pretty by itself
So I don't know why they bother
So what is a galaxy?
This is a proposed view of what our own Milky Way looks like if we were looking down on it, of course
We're not because we're about right there in the disk
so we can't take a selfie of our own galaxy because it would require a lot of
Travel at for a long period of time or faster than the speed of light to get up here to take this picture
But this is based on scientific evidence
This is a pretty accurate
Portrayal of what our Milky Way would look like if we were to take a picture from it from the outside
Um, it's about a hundred thousand light years across the disk and it has on the order of a hundred billion stars
And it's made up of stars and gas
It's rotating but it's actually held together
By the force of gravity much like the force of gravity that holds us onto the surface of the earth. So
We're all familiar with it, right everybody has tripped and fallen fallen down. So
Gravity holds us to the surface of the earth. It's an attractive force that holds objects that have mass it attracts them together. So I
I'm being pulled towards this microphone and it is being pulled towards me because we both have mass but
It's a very small effect because we don't have that much mass. Whereas with the earth. There's a lot more mass to it
So we're pulled much more substantially to it. But at the same time we're pulling back on it as well. So
In space if you have two objects, they're being pulled together. And if you have many objects, they're all being pulled together as well
so it tends to pull things together pull dense structures together to even
Higher density this was proposed by Isaac Newton. We've had modifications to it with Einstein and general relativity
But the base level is accurate. So thank you Isaac
So
Gravity is what's holding us all together so we can say that this is a gravitationally bound collection of stars and gas
But it turns out that there was significant research done by a famous astronomer in the 60s named Vera Rubin who passed away recently
And she actually deduced that if you count up the mass from all of the stars and all of the gas in some galaxies
They're actually rotating so fast that um, they should just spin apart. They should just like fly apart
There's not enough gravitational force from the visible mass to hold it together into one piece
And so that's one of the main
reasons that we think that there's Dark Matter there's an invisible there's an extra amount of mass that we can't see that is providing the
Gravitational force to hold hold the galaxies together from flying apart
There are other pieces of evidence that we have for dark matter, but that's one of the main ones
So I'll add to this list. It's a gravitationally bound collection of stars gas and dark matter as well
Ok, so what do we know about galaxies from observations?
We've already talked like a little bit about what we know from observations. But let's when we look up in the sky
This is many of you may have seen this. This is the Hubble Ultra Deep Field
This is an image of sky
That was imaged for a very long period of time using the Hubble Space
Telescope and you can see a huge diversity in the types of galaxies that you see each thing here for the most part is a
Galaxy, you see, you know, you see some red guys here you see some blue ones
You see some kind of funky shaped ones that are interacting you see disky structures like this is kind of disky
There's just a huge diversity in terms of the types and the colors that we see throughout the universe
But the main types are
Are these red ellipticals because they they they tend to look like an ellipse and they're reddish
We're very innovative with our descriptions. I
Like to think of these in terms of eggs
So I like to think of these as hard-boiled eggs because they don't have a lot of features. It's not red
I guess if it were Easter, maybe this would be appropriate but
So hard-boiled eggs are like the ellipticals and then you have these blue
spirals or disk galaxies like our own Milky Way
which I think of like a fried egg because you've got that disc component and then you have like the yolk in the middle and
Then so those are the two main types
but then there's also kind of a third type called the irregular galaxies these
Obviously just don't fit well into a category hence their name and they tend to be very very blue
So I like to call them scrambled eggs
So but when we when we fly through the the Hubble ultra-deep field because of course the speed of light
only
Is this gonna move for me? Do I need to click again?
Okay, the speed of light only travels at a finite speed and so the stuff that's farther away from us
It takes light longer to travel to us and so as what this is an animation
We aren't actually able to travel at these speeds through space
as we see
stuff from more distant stuff
It's essentially at a younger stage in in the universe's evolution and what we can see from observations
Is that as you travel through this to more distant stuff?
You're essentially looking at the universe when it was younger and looking at these
Galaxies when they're younger and you can see that as we go farther back in time essentially two more distant objects
They tend to be bluer. They tend to be a bit clumpier
they're different, right? They're different than they are nearby which is to say
The universe the galaxies in the universe when it was younger is different than it is today
And we can simply deduce this based on the fact that the speed of light is traveling  at a fixed speed
so
so our conclusions here are
There are two major types of galaxies red and blue spirals and then there's these irregular ones which are kind of fitting
Filling in the gaps and then galaxy populations change with distance
What else do we know from observations about galaxies? Well the distribution of galaxies again, this is a fly-through we can't actually do this but
There the distribution is not just uniform throughout the sky. This is from the Sloan Digital Sky Survey a major
observational effort that took place of last ten or fifteen years and
You can see that galaxies are distributed in clumps kind of there are voids in between them
But you see these kind of filamentary structures
It's oftentimes referred to as the cosmic web because it's kind of this web-like structure of filaments where you see galaxies and where you don't
And this is a 2d slice through that volume and you can definitely see these kind of filamentary structures and clumps
Which is kind of weird, right?
you wouldn't I wouldn't naively expect to find this kind of structure if I just went out and and just
Observe the universe but this is what we see
So what do we know again a short conclusion case here? What do we know about galaxies from observations?
We know that there are groups of stars gas and dark matter. They're two gravitationally bound
We we know there are a huge number of them in the universe based on our observations
There's a huge diversity and types, but it's mostly ellipticals and spirals
the population changes as we go farther away i.e., as the universe ages and then
There's this weird distribution of them in space. But the big question is why right observations are great for identifying, you know
Categorizing these galaxies and learning facts about them
But it doesn't necessarily
Tell us why they are this way or how they evolve
Because for for the Milky Way to change in any appreciable amount takes hundreds of millions of years
The earth when it orbits around the Sun takes one year, right?
That's what defines our year, but for the entire solar system to go around the center of the Milky Way
Which happens it takes like 250 million years
Which is obviously much longer than I hope to be around or many of my astronomical colleagues
So we can't really study it just by observations alone
Fortunately, we have theory and computers in order to to be able to better understand how these things will form and evolve over time
So we can simulate these systems. I'll just take you through a quick scientific method here
What I do is computer modeling of galaxies, like I'm about to show. We represent in a computer kind of
a virtual volume a virtual space
Like a chunk of the universe and then we program in the case of the simulations that I run there
It's primarily a grid based case a grid based
Discretization of the volume and then you program in your dominant physics on whatever scale you're trying to simulate
In the case of the simulations we're going to show here that's primarily gravity which we already talked about and fluid dynamics
Just how fluids behave because much of the universe that isn't dark matter is is composed of like gases essentially
There's very little solid solid stuff out there, even though you're like, oh well, then I'm surrounded by solid stuff
I'm on a planet, but that's not how most of the universe is
We have to create initial conditions as a starting point for our simulation
because you have to start somewhere and
then we run the simulation forward in time accelerating time much faster than our our
Experience as humans in order to go over the you know, millions or billions of years
And then finally you analyze the results and try and compare with the observations that we have of the universe
So we'll do a few different kind of
Tests, we'll do one with how do we simulate star formation? So for this we'll start out as our starting point
We understand that stars form in giant gas clouds. The gas clouds are big clouds that are fuel for that star formation and
We'll run it forward
This is a simulation that I'm going to show that was done by one of the graduate students here
Mike Grudic who's actually giving one of the talks in the next six months. So stay tuned
He's really good speaker. And does some awesome science. So we start out in a big giant gas cloud
This is about a million times the mass of the Sun and what happens is overdensities become more over dense by gravity
Remember gravity's an attractive force and eventually you start to form stars in the center and the stars start pumping out
Light and and radiation and it blows out the gas that formed them and and then you're left with stars
And many times these stars tend to be blue because they're very massive stars. And so they're pumping out an enormous amount of radiation
But the Orion Nebula many of you may have seen the Orion Nebula is a good example of this in action
so this is a dense cloud where stars are forming and blowing out the trapezium stars the four stars in the center are these
massive stars that are blowing out much of the gas that formed them and
At the end you're left with blue stars much like you see in young stellar systems like the Pleiades which again we would see tonight
if it were clear, but
You're left with stars in clumps in clouds are not in clouds in clumps or clusters
From that initial star formation event. So young stellar populations tend to be blue
But as they as the most massive stars
Essentially die off and turn into supernova. You're only left with the redder
cooler stars lower mass stars
and then the those young stars as they're as they're so
Energetic and then turn into super novae they tend to drive these hot gas winds that
Blow off and we'll see some more evidence of that coming up
so
So enough with just stars. How do we simulate galaxies as a whole?
Well, remember our model for our galaxy the nice fried egg
We can we can what if we just take two of those fried eggs, and we slam them into each other
This is a movie from a simulation
that
Periodically so it slams these two galaxies together and then periodically switches to images from the Hubble Space Telescope
Of actual galaxies and what you can see is this this very simplistic model
Has two galaxies slamming together and it's able to reproduce
Many of the observations that we have of irregular galaxies
Remember the scrambled egg galaxies when we look up so these are kind of strange looking galaxies that are very blue galaxies
and
They're blue because as these galaxies slam together
They're inducing a lot of young star formation. And those young stars. Remember are very blue stars. I
Really like this movie
So, yeah, we can do a really good job then of
reproducing a lot of the observational characteristics of irregular galaxies
simply by slamming two galaxies together and showing that those irregularities are mostly caused just by
Interactions between two galaxies as they collide and their colors are also explained by that
But it'd be nice to not start with something quite so
Artificial as the two galaxies that we just set up here and then allow to slam into each other
it'd be nice to start out like
in their natural environment in the universe
So let's see galaxies evolving since the beginning of the universe, but for that we need our initial conditions
We need our starting point to be the the early universe. So what did the early universe actually look like?
That's a tricky question
but recall that Edwin Hubble's second discovery was all about
The expansion of the universe now everything is expanding and traveling away
So if you go back in time, then the universe is smaller
Right and everything's traveling out and you go back farther in time and it's smaller still and if you keep going back in time
Well, you get to the Big Bang when everything was kind of in the same spot and traveling outward
So we can look at
Distant, you know light that was emitted shortly after the Big Bang about 400,000 years after the Big Bang and
That's something called the Cosmic Microwave Background. So this is radiation
that's essentially been traveling unimpeded for the last, you know, thirteen billion years and
and it it has a fingerprint of what the early universe looked like so
It's essentially a map of what the universe looked like now for the most part. This is uniform in density
We're only looking at I think one one thousandth of a modification relative to a uniform background
But you can see regions of over density and regions of under density
So if we program that in to our initial conditions for a simulation, we can see how the universe is going to evolve
So this is a large volume of space. It's about 300 million light years across. It's a it's a
It's a simulation volume and as you can see, it's very uniform in its density distribution
But there are very slight over densities that are programmed from those
the observations from the Cosmic Microwave Background and when we run it forward with gravity on
You can see that very quickly you start to see structure that forms, and essentially what's happening
Is those very very slight over densities are better at attracting the gas?
Around them to them because of gravity because it gravity is an attractive force
right and it pulls stuff towards them and it
Enhances those and so it turns into this runaway effect and you end up with this filament restructure
Purely due to the gravitational effects
and
In fact, this filamentary structure looks a lot. Like what we saw when we looked at the distribution of galaxies in the universe
It's not uniform in the distribution
It's in these this kind of weird cosmic web structure, which is super cool, right?
because you know we were just able to to
To demonstrate the simulations can totally reproduce the observations just based on gravity and these slight over densities from the early universe
Finally we can we can look at how again this is our kind of cosmic web looking at the dark matter on the left and
On the right this is going to parallel the same rotation and we're going to see what the gas is doing
Not just the dark matter, which is the the bulk of the gravitational
kind of load
so the gas also falls along these filamentary structures that are defined by where the dark matter is and
In the nodes in kind of the intersections where these filaments cross you get a buildup not just of dark matter
but also of gas and in fact that gas starts to get
dense and form stars and you you you get
galaxies at those locations or many
Galaxies and in some cases and what's happening the colors here represent the temperature of the gas
So blue is cool. And then orange and red is hot. So what's what you can see is as galaxies form
They start having star formation that star formation remember?
Erupts in these hot energetic winds from supernovae and from young stars that blows out material and cause these causes these explosions
Over over cosmic time
But of course when we look at the universe
We can't see in dark matter glasses and it's awful often times difficult to see in
With telescopes to see what the gas itself is doing
But we'd also like to just to keep on this we can look specifically at us at a small region within
one of those knots to follow the evolution of a single galaxy not just a huge volume of space that
encompasses thousands of galaxies on the left
We're going to watch a galaxy right in the center here
In in its projected gas density and here we're gonna look at the temperature of that gas
And what happens is that over time? You see this filamentary structure like we saw before
Galaxies start to fall into our central galaxy it essentially merges with them it forms
hierarchically by eating its neighbors and when they fall in that cool gas
Which is red here falls in and it causes bursts of star formation
Which cause these hot yellow winds to be driven out and blow material away from the galaxy but really it's forming by
by just eating its neighbors, so
The Milky Way is always referred to as like a cannibal because it's like ah
And these simulations were done done here at Caltech by one of the professors Phil Hopkins
But of course we aren't looking at the galaxies in that gas or the temperature of the gas
We're looking in starlight when we look at a distant galaxy like the Andromeda galaxy. We're looking at its starlight
And so this is what that exact aleck see. We were just looking at just in the last movie
This is what it looks like as it evolves just from the light from its stars alone
So you can see there are blue patches from the young massive stars, but you can also see red and brown sections
that's
Dust that forms
And it blocks the light from from stars behind it much like if you were to stand in a dust cloud in the Mojave Desert
The Sun would appear much redder or darker because the dust is absorbing some of that light and scattering the blue light
But this yeah, this always gives me a little vertigo here but
But this is much what a galaxy I mean we just watched this galaxy evolve over 13 billion years
maybe this is only about 12 billion years or 10 billion years, but a
Significant period of time much longer than I hope to live
And and you can really see a lot of the structure that we see when we look at still frames of actual observed galaxies
So these are these are snapshots of that not just that galaxy but other simulated galaxies that the fire
Simulations have done and then these are actual observations of galaxies when we look up in the sky and obviously the colors weren't spot-on
but in terms of the general structure were
generally reproducing a lot of
Similarities between the types and the colors that you see in in observations and Ihnen simulations. Oh
And it's I don't want to go too much longer here but it's not like we're observing so
What about the future of our own galaxy the Milky Way so our own galaxy is
Here and we've got time running in billions of years
But our galaxy isn't alone. We've already talked about the Andromeda first
It was the Andromeda nebula, but now we were we refer to it as the Andromeda galaxy
It's kind of hanging out over here. And there's also the Triangulum galaxy that's part of our it's called the local group
now
over time over billions of years
These systems are going to merge and in fact, the Milky Way and Andromeda will merge to form Milkomeda
Because that's fun to say
But initially, we're both kind of bluish systems because we have active star formation
But as this these systems merge
They they they blow out a lot of the gas that's responsible for active star formation
And and they quench they stop forming stars. And so what you're left with is a more red
Elliptical population. So this is
Milkomeda will be a red elliptical as opposed to Andromeda and the Milky Way which are both blue kind of disky systems
But they made a nice time-lapse of what the view from Earth would be over the next eight billion years
So here you have the Milky Way and Andromeda
hanging there and then a billion years later and rahmat is like much closer and then it's really really close and then it's like ah,
Everything's going crazy and then you're left with just like Milkomeda
So you look up in the sky and you just see this kind of like reddish haze
instead of the nice disc structure of the Milky Way
But don't worry the Sun will have eaten the Sun the earth by then. So
But this is don't sell your real estate. That's like five billion years away. So
What do we know about galaxies from simulations simulations can reproduce a lot of the characteristics that we see in observations
For four stars for four how galaxies form by eating their neighbors and a variety of different
characteristics and
then for the last thing that I wanted to talk about these simulations are not in fact run on like an apple 2e
They are run on
Supercomputers so I have a clip from the movie The Martian which you may have seen
So this is the supercomputer that actually exists. It's not just in the movie. It's called the Pleiades NASA
Supercomputer and Donald Glover here is a young astrodynamicist
who is doing some calculations on the supercomputer. All these calculations are correct. Oh, that's great!
And he's very excited. So
There are some things that are accurate about this some things that are not accurate about this so computers like this do exist
This is a similar one to Pleiades. This is called the Blue Waters supercomputer. It's in Illinois. It's run by the National Science Foundation
And it does consist of these long rows of many many many different computers in a rack
so I think Blue Waters is on the order of
200,000
processors all operating in tandem
Fortunately, you don't have to go there to use it
You can use the Internet to connect your computer to it or it'd be very expensive and have a lot more
Carbon footprint if I had to go to Blue Waters in Illinois every time I wanted to use it
The room is kept very cool not so cold that you can see your breath
But it's it's very cool because you don't want the computers to overheat at the end of your calculations
It does not tell you that they're correct
but
But that's okay
So the general conclusions, you know
Galaxies are awesome
observations of galaxies have revealed all kinds of stuff that you know that the universe is full of them and they've been around for a
long period of time
simulations can reproduce many of those characteristics which is super exciting and
Don't sell your real estate
But we're gonna merge with our neighbor and form something cool called the mill comet of galaxies pretty soon if you have more questions
I have some of those movies on my website and if you want to get involved more with galaxy research studies
There's something call or even non galaxy research studies. There's something called the Zooniverse. It's for citizen science. You can go there and
Start identifying different galactic types and it gets used in actual scientific research
There's just too many for us to actually do and and computers and AI aren't very good at identifying different galactic types
So we have to rely on humans
So if you want to help out
That's one way to help out but there's lots of different tasks that you can help out with active research projects
So, thank you very much
So do you guys have any I'll take a few questions and then we'll we'll adjourn for the panel Q&A. Yeah
Okay, huh
So the question was about the discovery of
Galaxies that seem to have a ring or a couple of rings around the center of the galaxy
These are called ring galaxies
unsurprisingly
and
There we don't have a conclusive way to form these computer simulations try for a variety of things
There are different ways one is to have if you have a large disk galaxies and you like kind of send
another small structure through it it can cause kind of like
Like if you drop a stone into a pond and it causes ripples of material to go outward. It's that that sort of thing
but
But we don't yeah, it's unusual and we we don't have a really good explanation for these sorts of things
Is that so the question is is the grid simulation based on mathematical mathematical theory. Yes
So the way we represent hydrodynamics
Which is to say how how gases and how much of the universe is in fluid form and interacts with each other. We we
Typically represent it either on a grid based structure called oil Arian hydrodynamics, which is all math
I didn't want to get too detailed into the math here or
in a Lagrangian representative where it's all made up of particles particles that represent larger fluid elements, but
Yeah, it's all math. This is all math. I just didn't include equations because most of the time public talks get really boring
Yes, so the question is do we use the many-body problem we absolutely do
For the bulk of the gravitational calculations that we do in this
there's some component of the n-body problem, which is to say I
Initially when I talked about gravity gravity
I had four particles that were each pulling towards each other
That's almost always done in some way representing this many body or n-body problem
where you have many different
Particle masses that are that are being pulled towards each other and you're calculating the the attraction the gravitational attraction through through mathematical
formula based on
Newton's gravitational stuff that we talked about to you
Yeah, sure
The question is how do we
Incorporate dark matter and dark energy into the simulation since it's still active and we don't really understand it. So
very good question
dark matter
So it's true. We don't really understand what the nature of dark matter is
But we do have a really good understanding of how to parameterize how it behaves. Yes
I can't hold in my hand like this is dark matter
But I know I know how it behaves really really well on large scales. We treat it like a collisionless fluid
We use usually n-body
Representation of it where we have it as representatives as small infinitesimal particles
Consisting of a very large portion of mass and that seems to do a good job of representing it for the simulations
Even though I can't I can't conclusively say like what that what that matter is I can I can say how it behaves
Well, usually so the follow-up is would we show how we designed the dark matter to how we
Parameterize the dark matter to someone who's an expert on
astroparticle dark matter particle physics
Usually not
We're both like the observations of how these behave
we're definitely like we read their literature and they read our literature but
How how dark matter behaves
Shows up in a number of observational consequences that that dictate what they should be looking at and they dictate what we should be
Parameterizing in our simulations. So it's it's really trying to hit it from several different directions to resolve this problem
Yeah
When galaxies merge are there are there collisions between stars? Ah
So for the most part no, so when galaxies merge actually so, you know
We have our galaxy that's like the disk of the Milky Way galaxy is about a hundred thousand light-years across right?
But and there are a hundred billion stars in it, which is a crazy large number
But actually most of the space within it is just open space. That's why it's taken
You know why the nearest star to us is is three light-years away
Be and there's no stars that are closer three lawyers is like from our perspective is a really long ways away, right?
So it turns out that if you take two galaxies and you merge them together
There it's very unlikely that you'll actually have two stars hit each other or two planets hit each other. They'll just kind of go and
pass through each other
the one thing that won't go and
Pass through is gas because if you take a gas cloud and slam it into another gas cloud
It's not like fitting between you know, it's not like a sieve or something like that
they'll actually hit and they'll they'll slam together and they'll
Probably start a bunch of additional star formation. It'll cause shocks in the gas and over densities
That'll that'll trigger a bunch of star formation
So while we don't have to worry when the Milky Way hits
Andromeda that like the earth is going to go hurtling into another planet what we do have to well aside from the other problem that
the earth will be consumed by the Sun at that point but
the UH the problem that we have to worry about is that
Those slamming together will cause a bunch of star formation and that star formation will cause a bunch of
Young supernovae and the supernovae will be bad news for us because it'll cause these big explosions of gas and whatnot nearby
Yeah, if like if a nearby star were to go supernova it would not be great for us
be like a big piece of dynamite going off at your next-door neighbor's house like wouldn't be so great, but
But in terms of actual collisions, it's very unlikely
Milk Amida. Yeah, so the question is are there any virtual reality?
representations of these simulations or of of
How it would you know to see like the Milky Way and Andromeda merging and to my knowledge. No, but
There is a lot of active development in
visualization of scientific data sets like these done by people here and done by people at
various different supercomputing centers around the country, so
I'll put it on our list
Well, we'll try and do it I
Could probably take I don't want to keep everybody here
So I'll take two more questions and then we'll we'll pause and has anyone come in recently is it I'm assuming it's still cloudy
Right you gone
Okay, it's cloudy. All right, but we'll set up for the Q&A panel, but I'll take two more questions and then kind of adjourn
Oh
Hmm
Oh, so the question is sorry so everybody can hear how
How much brighter would the night sky be if we were closer to the center of the galaxy than where we are right now
it probably wouldn't be I mean
assuming like getting rid of the moon since obviously the moon is a major source of light in our night sky
It probably wouldn't be that much
Brighter if we were in near the center of the galaxy
But if we were close to so we're in one of the spiral arms kind of near one of the spiral arms
we we could be in a region like if we were closer to other stars other than just
The Sun it would definitely be brighter
but our nearest star is like three light years away and it's not a particularly bright star like Proxima Centauri is just like
It's like it's like a crummy star
I mean, sorry if there are a big Proxima Centauri fans here, but it's not it's not the greatest star
So if you're I would say that you could have a brighter night sky if you were closer to
An active region of star formation, but that doesn't necessarily mean that if you go into the center
You're going to be next to one
You just need to be like in a denser region in one of the spiral arms because most of the bright light in a spiral
Galaxy isn't just at the center
It's along those arms where there's active star formation, but that's a good question
And there was a gentleman in the back who had a good question. Ah
Why does it take so many supercomputers to make an animation like this it's not so much to make the animation the animation
many of one of the
The movies that I made here I ran the animation on my laptop. It's to run the actual simulation. That's very
Intensive because you're you're representing
Many many different
Computational elements usually fluid elements to represent how gas is moving?
Across the the simulation volume and you're doing that at a very very small scale relative to the to the large
Size of your simulation box. So for instance
these simulations are calculating how
How on the order of like a billion or maybe ten billion individual fluid elements are all interacting with each other?
which is really
it's really computationally expensive to do because this is a
You know
Going back to what the the gentleman asked before about the n-body problem
So remember I showed how gravity operated on four different particles
So each of those particles has to figure out what the effect is from each other system, right?
So there are four particles. I have to go. Okay, which way am I going to move?
I need to know about your mass and
Distance for me how much you're pulling me towards you how much you're pulling me towards you and how much you're pulling me towards you
But then when you add and each of those four has to do it
But then so it's called a Big O of N squared problem
It scales with the square of the number of particles. So in that case, it's four squared. So it's 16. Okay, no big deal
So we add another particle in then it it then it goes with there are five particles. So it's square
So it's 25 and each time. You add more you're adding the square of that number of particles
so
Ten billion is a large number but ten billion squared is a very very large number and it's really hard for our computers to do
That I'm sorry. That was a really long-winded and strange answer but
It's an N squared answer I was trying to live up to
to the difficulty of the computation there are advances being done in things like
Graphic processing units like GPUs that are used that were primarily funded by game development and visualization of graphic
graphics for video games that have helped in some ways to do this
So there's a lot of move towards having our simulations relying on this new hardware that's actually being developed
just to make video games cooler, so
Hopefully that'll that'll aid us and we won't have to use you know, these hundred million dollar supercomputers to do these simulations
Okay, I've yapped enough
All right
We're gonna start our panel
so I've taken the liberty of
Writing the things that Cameron does including
supercomputers galaxies simulations and ultramarathons
You should ask Cameron how he ran a marathon
Against horses and people and people riding horses and he beat all the people and all the horses
So resident ultramarathon man
Yeah, so maybe we want to go down the panel and introduce ourselves
So I guess I'll start
My name is Dylan. I am a third year grad student and I work on
Mostly explosions various kinds nowadays, although I used to work on galaxies
particularly measuring how fast stars form and
the technique that I use is
Mostly like radio astronomy so you can ask me about that if you want
I'm Rachel I'm a fifth year grad student and I'm working on
observations of distant galaxies with large telescopes and in particular I look at the gas and dust content of those galaxies and
What kind of chemical elements are in the gas and dust in those galaxies?
And I'm gonna give a talk this term so you should come to it next term sorry
I'm u-kwon and I'm a fourth year graduate students working pretty much the same as what Rachel was working on
Yeah, we're actually scientific siblings we have the same divisor and
I guess to make it more explicit
I'm more I work more on the gas and dust around galaxies instead of inside the galaxies and I also use
Big telescopes so that's it
You guys know what I do
So are there any are there any questions
Yeah, yeah, okay
Okay, so the question was can I describe the differences between
novae and supernovae and
There are many different types of supernovae. So there's a lot of detail that I could go into
but very briefly a
nova, or a classical nova is
Basically some runaway fusion that's happening on the surface of a white dwarf
So the white dwarf doesn't actually explode the star survives Innova. In fact
There are many novi that are known to recur that
There's one in Andromeda that goes off like clockwork every year and it actually went off like a few weeks ago
And so, you know, every time that goes off you see like some astronomer telegrams being like, oh we found it again
You know, here's another Nova
But a supernova in as opposed to Innova is one where the entire star actually blows up and the star is completely gone
There are several different flavors of supernova. So the one involving white dwarfs is called the type 1a supernova
Pay no attention to the names. They're really stupid and they're just historical like
oddities but a type 1a is basically a white dwarf that
Undergoes some sort of explosive burning in its core and there's lots and lots of debates lots and lots of conferences
Like arguing about how exactly this happens but basically a white dwarf has explosive burning in its core and the entire thing blows up
and that's type 1a they're important because we can use them as
Standard candles to measure how far away things are
There are type 1 bees which are
actually massive stars that collapse and
their cores explode
and their type 1 bees because
These are stars that have lost their hydrogen envelope so you can think of stars like onions and the outermost layer of the onion
There's hydrogen and then the second outermost layer there's helium and then you know
There's like carbon and oxygen and neon and stuff like that
but basically for some reason these stars have blown off their outer skin of hydrogen and
When those stars explode they're called type 1 beasts
There's type 1 C's which have not only lost their hydrogen that have lost their helium shell as well
And then there's type 2 supernova and there's like a million different kinds of type 2 supernova
I'm not gonna bore you with the details
But they're mostly also very massive stars that have collapsed and their cores have exploded
You can ask me more about specific ones if you're interested
Yeah, so the question was how exactly does a type 1a explode you have a white dwarf and
Historically the picture was that there's a white dwarf and there's a nearby star and the star is just losing
gradually some of its mass its spiraling in to the white dwarf and it's giving the white dwarf more mass and
Eventually the mass of the white dwarf gets so massive that it can't sustain its own weight and it just collapses under its own weight
And that's what causes the explosion
it turns out that there are many problems actually with that picture and
It's it's been
Understood more and more in the last like five years or so that I
the favored method for producing type 1 A's is
to white dwarfs that are actually very close to each other and
The details of which are get complicated
but one of like the popular ones nowadays is
Something called the the 6d model
Which is kind of a silly name it stands for
Oh is it?
Yes
Yes, okay. Dynamically driven double degenerate double detonation. Is that right? Yeah
Yeah
very very quickly
It's like two white dwarves that are spiraling into each other and one white dwarf like loses a lot of its
atmosphere to the other white dwarf and
for some reason which I'm not an expert in that
causes some
explosion on the surface of the white dwarf and that explosion
travels around sends a shock through the white dwarf travels around to the opposite pole of the white dwarf and
that creates another shock and when the two shocks meet inside the white dwarf that is your core detonation and
That explodes the entire white dwarf
It's controversial not everybody believes this theory, but this is one of the popular ones now it is so there you go
Yeah more questions
Yes
So the question was so Beetlejuice is a nearby giant star I actually forget what kind of star it is
Yeah, red supergiant I think a red supergiant, okay
Yeah, does anybody know what mass it is
You wrong is googling on his phone. So
What I will say, I don't know exactly what kind of start Betelgeuse is off the top of my head
what I will say is the
connecting
Types of supernova. It's 11.6 solar masses and there's a red supergiant
Okay, it's about a hundred thousand solar luminosities and approximately 92 total radii cool, okay
Alright so anyways Betelgeuse is au
2222 parsecs how many six hundred light years away cool. Okay, so
Betelgeuse is like eleven solar masses and is about at the low mass end of
The kinds of stars that will blow up
It's thought that the threshold for stars that will blow up versus stars that died by other means is like eight solar masses or so
So it's not like one of the monsters like 50 solar masses or something
So it turns out the connecting
Stars with the actual kinds of supernovae that they blow up with
It was tricky business there have only been like a few examples
super novae where you see the supernova and then you can go back into like
Historical images and actually identify like what star came from like it has been done but there's like it's been done like five times
My best guess is that it would just be like some sort of ordinary type 2 supernova
So just like a core collapse supernova of some kind but I don't know for sure. Yeah
Yeah
Yeah, very unlikely of the sun's gonna explode
Yeah more questions yes
Well, it's not that the
Everything's expanding away from is that the space itself is expanding?
So the the analogy that I've heard is like if you're baking raisin bread in your oven
so you have
raisins in your dough and then the raisins are moving away from each other because the bread itself is expanding and so it's actually the
Space-time it's getting bigger so you can think of a like a grid that you're drawing in your space and the grid points are expanding
So your space is your galaxies?
there's not gonna be a gap in between your galaxies because the space-time itself is expanding but actually
You know and drama in the Milky Way are so close that they will merge despite everything else moving away from each other
So everything's will be away. But certain things they were so close. They'll get too closer together if that makes any sense
Okay, so just think about
Expanding as a uniformly expanding
Space-time so that makes so that doesn't so
Basically, nothing is like stretching apart. It's just like you have
Your gas and you have your galaxies being more diffuse instead of just stretching out app from it
More questions, I saw a hand from somewhere in Africa
You mean a solar system or the galaxy
Dust exists inside galaxies for the most part because it has to be pretty dense to form dust
so I mean
I don't think the Milky Way is in a dusty area itself because the dust is inside it but the solar system
Would that be in a dusty area? I don't think so. I
Think we are
Yeah, I don't think we're in a particularly dusty area, but I'm not really sure
So I don't actually know but I recall
reading somewhere that we're in like a bubble of some kind like
Clear bubble, yeah
So maybe like, you know some supernovae went off like, you know
Millions of years ago or something like that and like cleared out some space. I don't actually
I I work on galactic dust not an entire galaxy but in other galaxies and the dust actually exists mostly in the mid plane
So not so much
up and above or below the
Galactic plane because it has to be dense to form to us and we don't know how it forms
But it could be even in supernova explosions. So you find them more in I
Don't know kind of crowded areas, which is why when you look up at the sky
You see the dust kind of like
Along the plane of the Milky Way if that makes any sense
And if there's more of it towards the center of the Milky Way because you're seeing a larger column of dust towards you
There questions
So there are ways to know it
So first thing is that you can't compare the colors so you can so basically galaxies have their particular color
That's different from stars. So you in a color diagram. You can actually pick out some kind of thick category
Well, you start well, you can start with red blue and green but astronomers invented other colors with
If you took a red filter on your camera and then a green one and then you subtract red from green
That's what astronomers call color
So if you you would take one color like red - green versus green - blue but not but not that but like some sort
Of analogy - that we don't we use we're kind of rude filters
But you can plot it on a graph and show like where the the galaxy falls is
Indicative indicative of what kind of galaxy it is?
Yeah, but you could also directly
See whether it's a galaxy compared to a star for example
Because if it's smudgy right like a star is so small that like you would never be able to actually see the structure
But if it's a smudge then it's a galaxy of some kind
Oh
Yeah sure. It could be a nebula nism kind
But if you have a spectrograph which you can use to
disperse the light into different frequencies and then you can see
How much light you have at each frequency?
Then that that can kind of form a particular shape that is more indicative of a galaxy versus Atkin nebula or a star
Because you have different, you know
Your galaxy is a composite of lots of different stars and mitting at different wavelengths because they're different brightnesses
and
Then you have gas in your galaxy of dust in your galaxy that emits a certain wavelengths and all sorts of things if you have
Enough of these like spectrograph and you have enough of observations different frequencies
You can construct kind of what your galaxy looks like over different frequency bands and what is composing it basically?
Well, it depends on how wide of a wavelength range your your spectrum cover
So we if it's a very very wide frequency range
you can definitely tell like a galaxy will look as a particular way because you have the Stars and the UV and then you have
Dust emitting in the infrared and the radio wavelengths
But if you just look it up like a short swap of it
You might only see you know composites of stars or you might look like a like clusters. I don't know
Okay, so super novae look very different from normal, oh so the question was
Sometimes you can point a spectrograph at a distant galaxy
Sometimes that galaxy is really small. So how can you tell the difference between a supernova and a galaxy in just the galaxy itself?
and so
There are a few ways. So for one
supernova
Especially when they're young tend to look very very different from galaxies
Right and one thing that you can learn from a spectrum is a spectrum has certain what are called lines
and those lines are just
Signatures of different chemical elements. So for example hydrogen has a very specific line called H alpha located it
6560 3 angstroms
In nanometers ok 6. Yeah, whatever. I mean, yeah, it's yeah, it's
With your eye as Rachel pointed out and
Basically if you look at a galaxy, um
You you can look it like how wide that h off the line looks like yeah
right
And that that with tells you about like how fast the gas that's emitting
The hydrogen gas that's emitting this h alpha line is traveling, right?
so typically for like a star formation region, you might see the gas traveling at like
you know 50 kilometers per second or something like that, but for a supernova you would see it traveling at like
10,000 kilometers per second. And so that line would just be like a mountain, you know
And you would see like all sorts of ripples in your spectrum
Yes
Yeah, exactly
Mm-hmm
Yep
Your spectrum would evolve over time see if you point respect your guys at it at a different period of time it would look different
Than you first discover the supernova. So you point it back again a few days later
I mean a few weeks months later. It would look really different
Yeah, I mean there have been supernovae and nearby galaxies that you can actually point your amateur telescope at and see them my dad as
An amateur astronomer and he's like he's looked at supernovae. I think a few times with his telescope
Maybe he's just wanted to but he hasn't been able to
So, I think you actually can't see them if you
Look at the right nearby galaxies view a big enough telescope in your backyard. You can do this
Yeah, so the question is how long is a supernova lasts that depends very strongly on the supernovae and it depends on very strongly on
What wavelength you're looking at? So
There's certain supernovae that
Lasts only for a very short amount of time. So
There is a famous
explosion
Very recently called a T 2018 cow. I just like the name
So, you know the the first supernovae to be discovered in a year is just a you know, the next one is B
Right and then when you get to Z, then you start with like a a and a B and stuff like that
And so now we're finding tons of them and we're getting to like Co W
And it happened to be a particularly interesting one and happened to have a particularly interesting name that one actually
Rose extremely rapidly, it brightened by almost like a factor of a hundred within like a day or two
and
it faded I
think like
Over the span of like a week or two or something like that
there are other supernovae this is one of the like, you know alphabet soup supernovae called type 2 peas that
Sort of brighten up and then they the P stands for Plateau. They've just flattened out
For like months and then they fade away
So this is like the traditional way of looking at supernovae, which is using visible light
kinds of kind of light that your eyes can see
you can look at supernovae the infrared and
We have a friend named Jake who does this as a grad student here and they can last for years in the infrared?
I work in the radio. I actually read a paper
very recently that
Was talking about like observations done in like the 2000s of a supernova
I think it was
1957 d and it like it was like 50 years later or something like that and you can still see it in the radio
So it depends very strongly anything from like days to like decades
Usually yeah the longer the wavelength the longer the period you can observe before usually yeah
Yeah, so the explosion itself
It depends on what you define is the explosion, but it doesn't last for very long. So what happens?
Let's say we have a massive star that collapses and its core starts to explode
Well, what's happening when the core is exploding is that the rest of the star is still collapsing?
It doesn't know about the explosion yet
And so the explosion starts to like rip through the rest of the star
And you have this shockwave that's like going through the entire star
You can't see the supernova yet. None of the light is able to descale because the light is just trapped inside the star
But when it reaches the surface you have something called the shock breakout. This has actually been observed. I believe twice
once was just the super super lucky amateur astronomer who was like
Taking a picture of this galaxy and like was like wow
there's like a bright thing that just appeared like over the course of the night when I was looking at this galaxy and
It turns out that that was the shock breakout
And it was like one of the two that have been ever been ever been observed or something like that
they're probably more than two was just two that I know of another one was just
something that was
also super lucky
An astronomer who was at Caltech. She was a grad student here Alisha Soderbergh she
was
Pointing an x-ray telescope at this galaxy trying to find like the afterglow of a different explosion an entirely unrelated
explosion and she happened to find like
You know a supernova that had just added stock breakout and turns out that rock breakouts are very bright in the x-rays. Okay?
Anyways, I got on a tangent there
Basically, you can get very lucky
but after after the shock
Ripples out to the surface of the star then you can start having gas that's ejected
right like the insides the guts of the star just being thrown out in the explosion and
And so that takes like a few hours so for that to happen and
then afterwards
The stuff is just expanding and it's cooling and there's like radioactive decay that's happening in it
that actually powers a lot of the light that you see in a supernova and
All sorts of things happen and
that those are sort of the embers that are
That you were referring to that are just cooling. Mm-hmm
Yeah
So the question was is there any relationship between the amount of energy in an explosion and
How fast?
It changes
I
Should know the answer to this question I
Think it's a little bit complicated in the lay there many different energy sources
In a supernova, so I mentioned briefly that
Radioactive decay is important. So in particular
It's nickel-56 decaying into iron-56
The produces a lot of the light that you see and the plateau is just
due to a lot of this nickel decay and
That
tends to have about
like 10 to the 51
Orgs are just a unit of energy that astronomers use but nobody else uses
They're like very very
Violent explosions that may have like 10 to the 52 orgs like 10 times more
Called gamma-ray bursts that are associated with like certain types of supernova
but
Whether and those are actually very fast, so
Tentatively, yes the shorter the explosion maybe the more energy, but I think there are lots of exceptions to that
Yeah
Yeah, so the question is how do we know that without being
Observing from outside. How do we know the shape of galaxies from inside?
That's actually a very good question
Astronomers have been struggling for a long while to actually know what shapes our own galaxy is
So for a long time people actually just
thought that our own Milky Way galaxy is actually just the tween of
M31 the Andromeda galaxy you just mentioned. So in a lot of old diagrams you see that
People were just drawing the Milky Way galaxy
Exactly the same as the Andromeda galaxy
But that turns out
Exactly exactly. That's right
But as time evolves as astronomers did a lot of more observations people start to realize that that's not the case
by so how did astronomy know that is basically just to see
the Stars just to count the stars around us and
to kind of densities to count the distance and then you will figure out how the three-d
distribution of those stars are at least around or or
solar system
So more recently
Astronomers have launched a satellite called Gaia which is actually extremely good at counting stars
so this
Set like this this telescope
has been
observing for like three years maybe and
with its very high precision if measuring where the stars are as
Cameron mentioned in a lecture you can actually figure out with the parallax figure out the angle
difference while
the earth is orbiting the Sun so you can actually
Measure very accurately. Where does how far the star is?
So by doing that we actually have a very good sense of how the Milky Way is right now with thanks to that light
And you can also measure the distribution of the gap by dense gas the Milky Way
We're looking at electronic transitions of hydrogen when it's very cold it
the
Kind of the state of the atom kind of flips up and down you can you can see that and actually measure where the cold
Gas is in galaxies make maps of that. I
Will answer the first part and I'll answer the second part. So the first part is how far
do we need to go before we can actually take a head shot like a
well a selfie a
Selfie of the Milky Way. Well, the radius of the Milky Way, let's just say the disc is approximately 10
kilohertz, there's
10,000
30,000 light years. So you need to
Go approximately that far above the yeah perpendicular to the plane to actually see the disc
And then as to whether there is dense gas or dust blocking our view if we were to go out that far
There actually is there is gas surrounding the Milky Way, but it's very diffused gas
I don't think it's nearly as dense as what you would see if you were to look up in the sky and see like dust
Lanes in the Milky Way, that dust is resides in the the middle of the plane and the disk of the galaxy and there's gas
Surrounding it but it's very diffuse and Dylan's drawing a diagram
So you have the milky way's kind of a disc right and then there's a bowl to this end of the camera
And it's talking. There's also a diffuse halo of gas surrounding it
And then inside of that there was like a few stars that are just kind of dispersed around
The fried egg model
Now you'll see more you'll see more but the as as Rachael was saying the said there's the fried egg
Which is mostly composed of gas and stars
And dust and then there are there is more stuff in the larger volume around it
So the gravitational influence of the galaxies extends out about ten or twenty times farther than that
But there's very little stuff out here. The density of stuff is much lower
So that's why when you look at distant galaxies, you just see the fried egg. You don't see the much larger sphere of stuff
That's surrounding it because it's so low density that it's not emitting very much light
That's right, you can see the stuff you we can see out of our galaxy
easily
You know when we look at the Milky Way in the night sky, you see that the the plane of it across the sky
but if I look out in that direction where I'm not looking in the plane of the Milky Way
I can see very well because there's just not as much stuff in that direction in the direction off the off the disk off the
The white part of the fried egg to keep with this ridiculous analogy
Okay, so the question was
If dark matter behaves in a in a collision 'less manner there's no friction
Then why does it lose enough energy to flow into?
Filamentary structures on large scales. That was the question, right? Okay
The main thing is that it's not really frictionless it is losing energy with time
And that's essentially done
There's something called dynamical friction
Which is not friction in the in the way of what you think of where you rub two structures together
But it has the same effect friction is essentially a way of dissipating energy
Usually kinetic energy motion energy in a different form usually heat
In the case of dynamical friction, essentially what's happening? It's kind of a weird effect if you have
many
As in are as in our galaxy if you have many small particles will call them stars
but they could also be dark matter particles and
And you send a more massive structure through that
kind of sea of these particles
Its gravitational influence is going to attract things towards it
but if it's moved a
substantial distance in the time that those things are traveling towards it it'll build up kind of a wake behind it and over density of
Structure behind it. That stuff is more massive than the stuff in front of it. So it's pulling it backwards
so it's losing energy as its flowing through this sea of
Material that energy is going into the build up of structures behind it
But effectively this is a way that you can get when galaxies merge if they were totally frictionless, then they just turned into orbits
But they slowly lose energy and collide and coalesce into a single structure. So
That's essentially to just answer how you could have an effective friction even without having things rubbing together a loss of energy
in this form
But yeah
That's that's one way that you can effectively get structures to form out of a kind of a relatively uniform
Background instead of it it just flying through. It dissipates. It dissipates large-scale motions in this way
Yeah, it's like a turbulence kind of thing it's a cascade of motions from large scale down to smaller scale
There is some loss of energy from gravitational waves but not usually on that kind of scale
So the question was if we're not sure at which time
Baryonic matter like protons and electrons formed versus when dark matter formed. How can we have some sort of?
chronology to how the simulation proceeds
To mimic reality
The the dark matter or the
Baryonic matter is forming in a very very short period after the birth of the universe. We're talking like less than a second
and
So whereas these simulations I showed the Cosmic Microwave Background
that's usually what we're using as our initial conditions for the simulations and that's about
Like four hundred thousand years after the birth of the of the universe after the Big Bang
So at that point the dark matter is is fully
Manifested and the baryonic matter is fully manifested and they've been hanging out together
You know doing their thing for like a few hundred thousand years
so it's not really a problem if we were to try and go back beyond, you know to very very early periods like
Less than a second. This would be a problem, but we
Don't dare go back that far cuz we don't really have it's all theoretical
Constructive of what's going on at that period we don't have a lot of observations from that era
Absolutely, oh
Great question
There's a whole committee that so the question was who?
Who gets to tell the Hubble Space Telescope?
Where to point is that basically the question and do we ever have any say in where it points?
Yeah, so so scientists and even non scientists could
potentially propose essentially this it's run by NASA and
as many Space Telescope's are and
it's a it's paid for with public funds taxpayer funds and so it's a resource that any
American can
Write a scientific proposal and say I want to do this science project and in order to do it effectively
I need the Hubble Space Telescope to point at that object over there for an
hour, or
20 hours or something like that
And if you do that
Then that should give me the data that I need to solve this important question about
the origins of the universe or how stars evolve or something like that and
then a commit a lots of people submit these sorts of things usually from
Academic institutions like Caltech and then there's a committee that's made up of people from the scientific
Community but not the ones who are submitting so they're not like oh, yeah, I'll accept my proposal
You know
There's no political aspects there
And I've sat on one of these committees and and you go through and you read all of these proposals
They're usually like 10 page long proposals and you read them through and you're like, oh this is pretty good as well
It isn't pretty good. And and you decide you only have so much time that you can allocate for that next year
You decide who who whose project is
Is the most interesting and the most efficient like maybe this one's really cool, but it needs like 10,000 hours of observing
Whereas there are many better ones that are there
there are other good ones that need a fraction of that period
and so then you you you rate them and say this one is good or this one is bad and then there's a
There's some program officers at NASA who decide ultimately who who gets the time and who gets the money, but I just proposed
Not for observing time on Hubble because I mostly do theoretical work
So I propose to get money to support the work that I'm doing that's mostly used for the interpretation of observations from Hubble
But it goes to similar panels
Yeah
Do you guys want to add anything?
I'll add that Hubble has a cool twitter account where you can actually it'll tweet where it's pointing at any given moment
It's amazing. If you want a log on it'll tell you like which astronomer like requested to be pointed this direction
It's kind of cool and a lot of large telescopes are actually allocated time this way like we propose for the Keck telescopes in Hawaii
in a similar manner which is a certain number of institutions that kind of combine together to form the
the get time on this telescope and so
That's also how the supercomputers that we use also
allocate time on the computers via this method you propose to do a cool project because they only have so many resources and
again
The the supercomputers that we usually run on are either run by NASA or the National Science Foundation or the Department of Energy
And so you propose and say I want to use the computer to do this project and they're like, okay. Here you go
And then you can run it on the supercomputer for however long you need. But yeah, it's just a
democratic way of
Of doling out a shared resource
To you know, a subset of of all the people who apply
Yes
Yes, definitely. Do you want to talk about?
Yeah, so I've never actually done it myself but I've had it oh sorry, um suppose that there's some sort of
you know, very
Fast evolving event that happened and you need data now
Otherwise your supernova is gonna disappear or something like that
Can you like put in an emergency proposal into?
Some telescope and I get time and the answer is yes
I've never actually done it myself
On like super short timescales, but I've had it happen to me. So I was observing
I was in Hawaii actually observing on the Keck telescopes where
This is like a week after
perhaps one of the most important explosions like the decade the first neutron star neutron star merger happened and
What happened was I got a phone call?
From Montse Cosley wall who was like one of the professor's here and she was like, I'm sorry
I'm taking the first hour of your night because we're gonna start like we're gonna observe this neutron star merger, and I was like,
Okay, cool. You know this is much cooler than like what I would have been using that hour for so
yeah, so the way that this works is that
prior to
The actual event happening
She actually submitted a proposal saying if there was such an event to happen then
I'll be able to like interrupt for like one hour and get the observation that I need. And so
You can do that basically with most telescopes
Target of opportunity. That's what it's called. Yeah
The Hubble yeah. Yeah same thing
In fact when that happened Montse costly wall the professor that he was alluding to here
The the Twitter account that runs that runs the Hubble Space Telescope and says, oh I'm pointing at blabbity blah
because of this professor it tweeted that
That it was looking at an object from that
Montse costly wall had observed and it was supposed to be a secret because it was it hadn't yet?
There was an embargo on that news to the scientific community there only a hand
Well, there were a decent number of people within the community that knew about it, but it wasn't supposed to be tweeted publicly
And so it was kind of like oh shoot
We need to delete that tweet because it revealed this information about that. The Hubble Space Telescope was observing this this target of opportunity
from this explosion
But yeah
almost all telescopes have this that if they're if there's a certain set of conditions like an emergency, we've got a look at
That comet that's gonna hit the earth right now or whatever like everybody's like. Okay, let's let's go let's switch
There's no there's no battling to the death in the room no, yeah
Trip to Hawaii
So the question is what's the benefit of actually
Going to decide to observe instead of just doing a remote observing like we can actually control the cocktails going Hawaii here
In one of those remote serving rooms in this building
I guess
so
One of the benefit is that you can actually be
Face to face to the support astronomers. So when you control we are scientists actually
Using the telescopes. There are other people doing their job to support you and so for example
There is support for honoring the Keck Observatory who are actually well trained
Astronomers who?
Supports you in a way that how you can use this instrument to achieve your size goal more efficiently
There are also telescope operators who actually help you to point to the target
I guess the benefit is that you can actually have a face-to-face
exchange with them and
Why it's important is that for example when this is a new instrument like Keck had a new instrument a
Year ago or two years ago. I can't remember
and after its commissioned
We are actually one of the first people to use that instrument and we don't
Know a lot of the instrument how to use it and like how to correctly
more efficiently to point our
telescope to point our instrument to observe the targets we want to observe that will be the chance that
Being going to Hawaii to observe on site being very beneficial
And there are a lot of telescopes and kik is not one of these but there a lot of telescopes that are in more remote
Locations that you actually can't you don't have a good enough internet connection to do remote observing
so you have like the ones in Chile you have to go there because the internet is not good enough to do it remotely from
here in California
Yeah, and one other thing is sometimes especially when you have several nights in a row
It's nice to just like be on site and not have distractions
so I was talking about this Evan Kirby who's another professor here and he is this like
Adorable little like a five month old puppy or something like that at home and named Panda. She's the cutest puppy
Except she is like so hyper she will like, you know endlessly lick your nostrils and this is like really nice during the day
Right, but you don't want that after like you've stayed up all night, and you're just trying to sleep
I mean, this is actually the reason he's cited for like why he goes to Hawaii
I mean, there's also like
You know a really nice facility just for sleeping like at the observatory
So after you've stayed over all night, you really don't want like the sunlight interfering with your sleep
And so they have these hardcore shades like they're actually like wooden you clothes
