Greetings and welcome to the
Introduction to Astronomy.
One of the things that I like
to do in each of my introductory
astronomy classes is to begin
the class with the astronomy
picture of the day from
the NASA website that is
APOD.NASA.GOV/APOD.
And today's picture for
September the 3rd of 2019
well it's titled Unusual
Signal Suggests Neutron Star
Destroyed by Black Hole.
So what does this mean?
Well, this is a short
video clip simulating
what may have happened
based on detections
by a gravitational wave event.
Now what are
gravitational waves?
Well, they are what is emitted
when anything with mass moves.
So if you're moving around
you emit gravitational wave
- the Earth moving
around the sun
would emit gravitational waves.
Any motion of any
object with mass
would give off these
gravitational waves.
And it was a prediction
of Einstein's theory
of general relativity
over 100 years ago.
But only in the last couple
of years has it been detected.
So this did this
detection here is
another one from just a
couple of weeks ago detected
by LIGO and the Virgo
detectors and what
they do is look for
oscillations in materials
and very sensitive observations
that need to be made and made
at multiple locations, so
that any local effects are
eliminated.
So what this suggests based
on the observations here
is that a neutron star was
destroyed by a black hole.
Now as you play this
simulation and watch the video,
you will see the neutron
star first in the foreground
and then you'll see a
flash to another side
as the neutron star
has been torn apart
and is now spiraling
into the accretion
disk around the black hole.
So this is what happens
around the black hole
we can't get any information
from the black hole itself.
But as the material
spirals inward
it can heat up
within that accretion
disk to extremely
high temperatures
millions of degrees.
And that is where the
energy is given off
and where we can
actually see things
that is just outside the
event horizon of a black hole
meaning that we can actually
get information from there.
Once you cross
the event horizon.
No information can be obtained.
Now one of this
based on the best
fits that we're able to get it
says that one of these objects
is about five solar masses well
above the limit for a neutron
star.
So if something is five solar
masses a compacted down.
There's nothing else that it
can be other than a black hole.
The other one seems to have
a mass that about three times
the mass of the sun
or less than that.
That is definitely in the
candidate range for a neutron
star a neutron star
will have a mass
of a couple of solar masses.
And so this is a good
candidate for a neutron star.
But of course, there is
some uncertainty there.
So it could have been two
black holes for example,
as you could get a black hole
with a mass of just a couple
of solar masses as well.
So as we study more of these
and are able to study things
with more detail
we hopefully we'll
be able to learn more
about this type of event.
And in this case, we
do see the simulation
of what might have happened
long ago that gave us
this gravitational
wave event that was
detected just a few weeks ago.
So that was our picture of
the day for September the 3rd
of 2019.
It was titled Unusual
Signal Suggests Neutron Star
Destroyed by Black Hole.
We'll be back again tomorrow
for the next picture previewed
to be Spider versus Fly.
So we'll see what that
is about tomorrow.
And until then have a
great day, everyone.
And I will see you in class.
