Due to the crazy technological challenges that had to be overcome
in order to detect gravitational waves,
some people were skeptical that scientists had actually done it,
that they’d actually seen gravitational waves from black holes
after all, there was no corroboration
But,after the discovery that’s being announced today,
there can be no more doubt
because scientists have detected the merging of two neutron stars
a hundred and thirty million light years away.
This is the first ever detection of gravitational waves from in-spiraling neutron stars,
from in-spiraling neutron stars,
and what’s really exciting about this detection is that
the same event has been observed with telescopes
in all areas of the electromagnetic spectrum.
It all began on August 17th at 8:41 a.m.
Eastern Time when LIGO interferometers identified a clear
a clear gravitational wave signal that lasted about a hundred seconds,
which is way longer than any previous detection
and it’s consistent with theoretical predictions for the signal
from two merging neutron stars. [“hear” the sound of two stars colliding ♪]
Around 1.7seconds later NASA’s Fermi gamma-ray telescope identified a burst of gamma rays.
For decades gamma-ray bursts have been thought to
come from neutron star mergers,
but the evidence has been lacking
to know for sure that these gravitational waves and the gamma ray burst
came from the same event.
The key was to locate where in the sky this neutron star merger occurred.
Unlike a merger of black holes neutron stars
emit light when they smash together and continue emitting electromagnetic radiation afterwards
The Fermi gamma-ray Space Telescope
identified a large patch of the sky
roughly the size of six thousand full moons.
Using the European Space Agency’s integral gamma-ray satellite,
they were able to narrow down that range.
Now,the gravitational waves detected
by LIGO allowed them to identify two long strips in the sky,
one of which overlapped with the existing search area
有趣的是 Virgo 它是最新的引力波检测器
Now,interestingly,Virgo,which is the newest gravitational wave detector
which is in Italy,it was online at the time,
and it should have easily
been able to detect these gravitational waves
and yet,it saw almost nothing,
and that was kind of a key clue
because it indicated that the gravitational waves must be coming from
one of that detector’s blind spots.
Every interferometer has some blind spots
but if the waves are coming at that angle
it’s symmetricwith respect to the two arms and so it just can’t be detected.
So this helped further narrow the search area
down to the size of about
144 full moons
Now,within that area,
around fifty galaxies were identified to be studied with optical telescopes
and just 11 hours after the initial detection astronomers
located a bright spot in the galaxy NGC 4993.
You are seeing here pictures of the light
from two neutron stars that merged
130 million years ago.
Watch how the color and brightness changes in the aftermath of the collision.
So what are neutron stars?
Well,they’re the leftover cores of big stars that have exploded –
they’ve gone supernova
Now,those remaining cores are squeezed down by gravity
and if they’re too big,
say larger than two or three solar masses
well,they will keep on getting crushed until they collapse
until they collapse in on themselves forever and become a black hole.
But if those cores are a little smaller
say 1.1 and 1.6 times the mass of our Sun,
as they were in this case
well,then they get squeezed still
and so electrons merge with protons to form neutrons
and neutrinos and the neutrinos take off
and the neutrons are left
in a really really densely packed star.
And the only reason the neutrons don’t
don’t ‘combine with each other is because of a quantum principle,
the Pauli exclusion principle
that basically says you can’t put two of these particles
right on top of each other,
and that’s actually the only thing holding that neutron star up
So if you have two of these neutron stars
of these neutron stars and they are orbiting each other, well,
then they emit some of their energy as gravitational waves,
and as they do that
they lose energy, meaning they spiral
in closer to each other and when they get really close
you’ll see a few hundred kilometers apart,
the gravitational waves become intense,
allowing us to detect them hundreds of millions of light years away.
The collision of neutron stars creates a kilonova which spews debris out into space.
This is debris that glows,
allowing us to observe what’s been created
and in fact, the new observations with light telescopes
have shown that heavy elements
like gold,lead and platinum were made in this event, and that
and that helps us understand where a lot of the heavy elements
in our universe come from.
In my view, this event really shows us
that we’re ‘in a new age of astronomy.
We can detect gravitational waves, not just from black holes,
but now from neutron stars,
we can use that information to locate places
in the sky where that occurred and we can validate
that with our other telescopes looking in all parts of the electromagnetic spectrum
So,now we really have more tools to understand our universe
and I just can’t wait for the questions
that we’re going to address next and all of the different things
we’re going to be able to study as the gravitational wave
observatories get better and better.
It’s a phenomenal time to be studying the universe.