Maybe we really can use black holes to travel
the universe…
Hi everyone, what’s up ?
I’m JH aka DOZgeek, back here with you and
Section 51. Thank you again to watch this
new video.
Scientists have been looking into black holes
since 1783, when scientist John Mitchell first
proposed the idea that they were possible.
And after all this time they were still a
mystery in many ways.
Black holes are also infamous for being photo
shy – but since April 10 2019, history
was made and all that is about to change.
As their name suggests, black holes are invisible
to the naked eye. Theorized points of infinite
density where beyond a critical radius – known
as the event horizon – no light can escape.
So how is the invisible now visible ?
Well, firstly it should be noted that although
not directly visible, their over whelming
presence can definitely be seen. These enormous
cosmic objects have a huge gravitational pull,
which distorts spacetime and superheats the
surrounding material. So, it is these effects
that can be observed.
For example, in a binary system consisting
of a black hole and a companion star, the
black hole will accrete matter from the companion
star – if the accreted matter has sufficient
angular momentum it will not succumb to the
intense pull of the black hole and will instead
form a disk – an accretion disc. It is this
matter that can be seen – which although
revealing it was just not revealing enough.
However, Einstein’s theory of general relativity
predicted that if the surrounding material
is bright enough then the black hole should
create a shadow which could be observed. Such
an observation would require an extremely
high resolution, of which had never been done
before. Moreover the theory of general relativity
predicts that a sufficiently compact mass
can deform spacetime to form a black hole.
The Event Horizon Telescope project therefore
set about trying to achieve this. Utilizing
a global collaboration of 8 radio telescopes,
one of the greatest telescope arrays was created.
On April 10th 2019, those efforts have paid
off and the first image of a black hole has
been obtained. Amazing pictures of a black
hole for the first time in the human history.
Located 53.49 million light-years away at
the center of the Messier 87 galaxy, the whopping
6.5 billion solar mass black hole, M87, was
successfully imaged - providing the first
direct visual evidence of a supermassive black
hole and its shadow.
The telescopes contributing to this result
were ALMA, APEX, the IRAM 30-meter telescope,
the James Clerk Maxwell Telescope, the Large
Millimeter Telescope Alfonso Serrano, the Submillimeter
Array, the Submillimeter Telescope, and the South
Pole Telescope. Petabytes of raw data from
the telescopes were combined by highly specialised
supercomputers hosted by the Max Planck Institute
for Radio Astronomy and MIT Haystack Observatory.
The construction of the EHT and the observations
announced today represent the culmination
of decades of observational, technical, and
theoretical work. This example of global teamwork
required close collaboration by researchers
from around the world. Thirteen partner institutions
worked together to create the EHT, using both
pre-existing infrastructure and support from
a variety of agencies. Key funding was provided
by the US National Science Foundation (NSF),
the EU's European Research Council (ERC),
and funding agencies in East Asia.
The image shows a bright ring formed as light
bends in the intense gravity around a black
hole that is 6.5 billion times more massive
than the Sun. This long-sought image provides
the strongest evidence to date for the existence
of supermassive black holes and opens a new
window onto the study of black holes, their
event horizons, and gravity.
At the centre of the black hole is a gravitational
singularity, where all matter is crushed into
an infinitely small space. The black hole
lies 55m light years away from us. It is around
100bn km wide, larger than the entire solar
system and 6.5bn times the mass of our sun.
Through creating an image of a black hole,
something previously thought to be impossible,
the EHT project has made a breakthrough in
the understanding of black holes, whose existence
has long been difficult to prove. The image
will help physicists to better understand
how black holes work and images of the event
horizon are particularly important for testing
the theory of general relativity.
Now here are 5 Things you probably didn’t
know about black holes :
1. Black holes used to be stars
Stars live a very long time but, just like
us, they don’t live forever. They slowly
burn through the fuel that keeps them shining.
When they run out, one of three things happens,
mainly depending on its mass – the star
will transform into a white dwarf, a neutron
star or a black hole. If the star is big enough
(say 10 or 15 times as weighty as the sun)
it will explode when it reaches its end. The
explosion causes the star to cave in on itself,
decreasing its size dramatically. Because
the size of the star gets smaller but the
mass of it does not, the gravity surrounding
the star becomes so strong it absorbs everything
around it, including light, and a black hole
is born.
2. There are 3 types of black holes
Primordial: Considered to be tiny – these
range from the size of a single atom to a
mountain. Mountains probably don’t seem
tiny to you but space is a mighty big place!
Stellar: These are the ones most often found.
They are about 20 times bigger than the Sun.
Supermassive: The recently discovered black
hole falls into this category. To be amongst
this group the hole has to be more than a
million times heavier than the Sun.
3. You can’t see them with the naked eye
The reason black holes are black is that the
gravitational pull at their centre is so strong
it consumes everything around it, including
light. Because there is no reflection, we
have no instrumentation that can detect the
hole directly. So what scientists do instead
is look for the traditional effects a black
hole has on its surroundings.
When a star is being pulled into the hole
it breaks apart and becomes distorted. As
it’s sucked in, the bits of matter from
the star move faster, create intense heat
and throw off a glare of X-rays. That’s
what astronomers can use to identify a hole.
4. Black holes helped create galaxies
While Astronomers aren’t entirely sure yet
what part the black holes have played in the
creation of galaxies, one theory is that a
large star exploded, a black hole formed and
the rest of the galaxy was created around
it.
5. There’s a black hole in the Milky Way
It’s believed by scientists that there’s
a supermassive black hole in the middle of
almost every galaxy. In fact, there’s one
at the centre of the Milky Way, known as Sagittarius
A*.
Because the pull of a black hole is so strong
you might wonder whether Earth is in any danger
of being sucked into one of the supermassive
varieties. Well, worry not. Sagittarius A*,
the Milky Way’s black hole, is 26,000 light
years from Earth - too far away for it to
affect us.
Now, as developed in many science fiction
stories, black holes could serve as gateways
to other worlds, either distant parts of this
universe or other universes entirely. But
the reality might be more complicated than
that. And outside of the sci-fi realm, dropping
into a black hole is a bad idea.
Even so, it turns out that people who enter a
black hole would have at least a slight chance
of escaping, either back into their own world
or to some exotic place. This is because black
holes actually bend space itself, and so could
bring points that are ordinarily distant from
each other much closer together.
An oft-used analogy is the bending of a piece
of paper. If you draw a line on the paper,
it follows the paper's shape and the line's
length is unchanged by bending the paper.
But if you go through the paper, the end points
of the line are much closer to one another.
Understanding this requires diving into Einstein's
theory of relativity as applied to gravity.
It's important to understand that a black
hole is not empty space, but rather a place
where an enormous amount of matter is shoved
into a teensy, tiny area, called a singularity.
In fact, the singularity is infinitely small
and dense. There's actually some debate among
scientists on this point, but it will take
a lot of time.
As one moves closer to the black hole, the
escape velocity — the speed needed to escape
the black hole's gravity — goes up. At a
certain point, escape velocity is greater
than the speed of light, or 186,282 miles/second
(299,792 kilometers/second). For comparison,
the Earth's escape velocity is about 25,000
mph (40,270 km/h) at the surface.
Since nothing can go faster than light, that
means nothing can escape a black hole. But
there's a loophole: A black hole doesn't suck
up everything around it, like a vacuum cleaner
or a bathtub drain. Its power extends only
as far as the black hole's event horizon,
whose radius is the distance from the center
of a black hole beyond which nothing can get
out. That radius gets bigger as more matter
falls into the dense beast. Perhaps it's better
to think of a black hole as a ball whose surface
allows matter to pass inside, but never the
other way.
What's inside that surface is one of the biggest
mysteries in astrophysics. Remember that most
scientists think a black hole is a singularity.
All the matter from whatever originally supplied
the black hole's mass (a star, for example)
gets crushed into a point that has infinite
density. If you were to fall into a black
hole, the usual description of such an event
says that you would first get stretched into
spaghetti by tidal forces, then crushed into
nothingness. Your matter would then add to
the radius of the black hole's event horizon.
Eventually you'd be emitted as Hawking radiation.
Physicist Stephen Hawking's calculations showed
that black holes give off photons. In doing
so, the black holes lose mass, because according
to Einstein's famous E = mc2 equation, energy
and mass are equivalent. Black holes eventually
evaporate, but you would be waiting around
a long time for that to happen. There's some
debate in the scientific community about how
long it takes for a black hole to evaporate,
because the Hawking radiation doesn't preserve
any information about the stuff that fell
into the black hole in the first place; but
the fact remains that being emitted as radiation
is still not good.
And what about wormholes ? So, there might
be a better way out of a black hole, though:
Gravity bends space. Think of a sumo wrestler
rolling on a mat, indenting the mat with his
weight. Any object creates a local "gravity
well. That well gets deeper toward the center
of the object. A planet, for example, has
a gravity well, but as you go toward the center
of a planetary sphere, the well flattens out.
Using the mat analogy, any normal object would
have a well shaped like a depression with
a finite depth.
Black holes don't behave like normal objects
… perhaps fortunate for the trapped individual.
The curvature of space just keeps going up
and up until you reach the singularity at
the center of the black hole, where that curvature
is infinite. Instead of a depression, you
just have a hole whose sides get steeper as
you go toward the center, until they are basically
vertical and space is shaped like an infinitely
stretched dimple.
And that's why it's a mystery. Scientists
use Einstein's theory of relativity to describe
the curving of space, but Einstein's equations
start to break down in the singularities of
black holes. These singularities are also
very small, and at that point, one should
see quantum mechanical effects. However, nobody
has worked out a way to make quantum mechanical
theory work with gravity, to figure out what
a singularity might look like.
It gets even weirder when you realize that
black holes aren't static. Realistically,
any object in space tends to rotate. That
means the singularity could, if it rotates
fast enough, becomes a ring, rather than a
point. A ring singularity could provide
a gateway to other universes, as in the 1994
sci-fi novel "Ring," by Stephen Baxter, published
by HarperCollins. So a black hole could be
a wormhole, a gateway through space and time.
The idea is so intriguing because when you
have a point singularity, no matter how you
travel, the singularity is always in your
future if you are inside the event horizon.
But a ring singularity can behave differently;
the part that crushed you into nothing doesn't
always have to be in your future, because
of the weird ways a ring singularity would
bend and twist space and time. However, the
concept of a ring singularity as a gateway
is far from a sure thing. First, nobody knows
how a ring singularity would come into existence.
The other problem is that whenever people
have tried to work out the mathematics of
a black-hole-made wormhole, they run into
problems of keeping the gateway stable. Without
a theory of quantum gravity, such questions
are hard to answer conclusively.
The other issue is that nobody has observed
stuff coming out of nowhere, as one would
expect if black holes could be gateways to
other universes. After all, something would
get through, even if by accident. One set
of theories even proposes that black holes
start whole other universes, causing other
"Big Bangs" — and our own universe was one
— but that idea is still controversial.
And last, one implication of black holes as
gateways is time travel. Because of relativity,
there's no such thing as "now" that applies
everywhere in the universe. "Instant" travel
from point A to point B anywhere in the universe
would also involve time travel, and you could
end up arriving somewhere before you left.
Physicist Stephen Hawking noted that since
no one sees time travelers today, at least
that's been reported, it seems unlikely that
time travel is even possible in our universe;
that would point to black holes being less
useful as wormhole generators.
So, what do you think of that ? Would you
volunteer to explore a black hole in order
to verify all these theories ? Or more simply
could we send a probe or a robot in a black
hole ? But I start dreaming, sorry…
Are we living in a real world or in science
fiction ? Are you listening to the future
DOZgeek or the present DOZgeek ?
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I’ll be back really soon. Open your eyes.
Watch the sky.
Live long and prosper !
