Astronomers have made the groundbreaking detection of two neutron stars colliding in a galaxy
130 million light years away.
They detected the gravitational waves AND the blast of radiation released from the collision,
observing a kilonova for the first time.
I know we’ve been talking about gravitational waves quite a bit here on the Guide to Space,
and a few episodes ago, I hinted at the tantalizing possibility that gravitational waves could,
maybe, perhaps, be used to detect colliding neutron stars.
You know, once more sensitive instruments came online, and physicists tweaked and tuned
them.
Well, it turns out such a detection had already been made when I recorded that, now, hilariously
out of date video.
But it gets even better.
At the same time they detected the rippling distortion of spacetime produced by the gravitational
waves, different teams of astronomers were actually able to watch blast of radiation
released by the neutron star using every wavelength at their disposal.
They detected the gravitational waves and then saw the collision in the sky.
I promise you, this is one of the biggest discoveries of the year.
So, let’s dig into the news.
Late last week, the European Southern Observatory teased us that they were going to announce
something on Monday, October 16th.
We didn’t know what it was, but they called it “unprecedented”.
Okay, that got my attention.
On Monday we all learned what it was, and the reality lived up to the hype.
A 8:41 am EDT on the morning of August 17, 2017, researchers from the Laser Interferometer
Gravitational Wave Observatory detected the ripple of gravitational waves passing through
the Earth.
Unlike the previous colliding black hole observations which lasted a couple of seconds, these ripples
went on for 100 seconds, indicating that this event wasn’t from black holes.
Instead, it was tied to the collision of two neutron stars; the remnants of massive stars
with 8-20 times the mass of the Sun that went supernova.
Two seconds later, NASA’s Fermi space telescope detected a brief blast of gamma radiation,
with the signature of a short gamma ray burst.
The long gamma ray bursts are fairly well understood, tied to supernova explosions.
But the short bursts have long been a mystery, although astronomers theorized that they had
something to do with colliding neutron stars.
In addition to LIGO, the VIRGO Interferometer in Italy also detected the gravitational waves
passing through the planet.
With three separate observations, the researchers were able to determine the rough direction
that the neutron star collision happened: an area in the constellation of Hydra covering
several hundred full Moons worth of area, with millions of stars.
They encouraged the worldwide astronomy community to go searching the region for the afterglow
of the collision.
From space, there was the European INTEGRAL satellite as well as NASA’s Swift, Hubble,
Chandra and Spitzer Observatories.
Ground-based observatories across the hemisphere scanned the region, searching for a visual
confirmation.
The European Southern Observatory’s 1-meter Swope Telescope in Cerro Las Campanas in Chile
was the first to find a new point of light, located in the galaxy NGC 4993.
Then other observatories followed up, viewing the spot across the entire electromagnetic
spectrum, from radio waves through infrared to ultraviolet, as well as the space-based
observations in gamma rays.
All told, 70 different observatories were trained on the unfolding event using 100 different
instruments.
Until this point, LIGO had only detected merging black holes.
And the problem with black holes, of course, is that they don’t give off any radiation
when they collide.
Nothing escapes them.
But neutron stars aren’t massive and dense enough, so radiation can escape them, so there
was an opportunity to find the explosion with the rest of the world’s observatories.
These two neutron stars had already experienced their share of catastrophe.
In a previous lives, 11-12 billion years ago, they were both hot massive stars that died
as supernovae, one then the other.
These neutron star remnants orbited around one another ever since, getting closer and
closer for billions of years.
One neutron star was 10% more massive than the Sun, and the other had 60% more mass than
the Sun.
But they were only 10 km across - the size of cities.
In their final moments, they were whirling around one another, hundreds of times a second
traveling at a third the speed of light, rippling the fabric of spacetime with gravitational
waves, until the their intense gravity couldn’t withstand the forces.
They broke apart, merged together and detonated, releasing the gamma ray burst, seen 130 million
light-years away.
Colliding neutron stars detected by gravitational waves and confirmed by other telescopes?
That’s amazing, but it gets even better.
And I’ll get into that in a second, but first I’d like to thank:
Andrew Ladzinski Patricia Pipkin
Joseph Salomone
And the rest of our 793 patrons for their generous support.
If you love what we’re doing and want to get in on the action, head over to patreon.com/universetoday.
From previous observations, astronomers already knew that NGC 4993 was approximately 130 million
light-years away, confirming the predictions made by the gravitational wave astronomers.
This is amazingly close.
The previous merging black hole observations were billions of light-years away.
The world’s observatories watched the explosion brighten and then fade away within a few days.
Astronomers realized that they were looking at a very special kind of short gamma ray
burst, one which had never been observed before: a kilonova.
You’ve probably heard that all the heavier elements in the Universe, were formed in the
hearts of supernovae explosions, when the force of the collapsing layers compresses
lighter elements into heavier ones.
But the models of supernova-generated heavy elements didn’t seem to match reality.
There had to be another mechanism at work, and one idea was colliding neutron stars.
Only these events could generate and distribute gold, platinum and other heavy elements into
the Universe.
In the cosmic wreckage blasting out of the collision, astronomers detected the source
of these heavier elements for the first time.
The gold in your wedding ring, the precious metals in your cell phone.
They don’t come from supernovae, they come from colliding neutron stars.
In a fraction of a second, an amount of gold equal to the mass of the Moon was created.
In fact, just one of these events generates the mass of the Earth in precious elements.
So that’s where it all comes from.
This was a very big day in the field of astronomy.
Astronomers were incredibly lucky to have two neutron stars collide so close to us.
I know, 130 million light-years doesn’t sound close, but it was.
Thanks to the three separate detections, they were able to determine its rough location
to direct astronomers around the world.
And by following up, they observed a kilonova for the first time, watching how these unique
collisions spread heavier elements into the Universe.
We now have confirmation that our precious metals are formed in events like this.
Since the gravitational waves and radiation arrived here on Earth at the same time, it
confirms Einstein’s prediction that gravity moves at the speed of light.
By seeing the same event in both gravity and radiation, astronomers have a new way to confirm
the speed of the expansion of the Universe.
As a quick side note, one cool part about this discovery is the massive collaboration
that happened across countries, universities, observatories and research agencies.
In the end, 4,500 separate researchers were co-authors on the paper announcing the discovery.
Ask for Comments: Well, what do you think about this discovery?
Are there any aspects of gravitational waves, gamma ray bursts or colliding neutron stars
that you’d like me to dig into any further?
Let me know your thoughts in the comments.
Of course, we’ll need a playlist, all about this amazing discovery and the related science.
First, let’s start with the original announcement from the European Southern Observatory, and
the announcement from NASA.
Here’s a video from Veritasium on the event.
And of course, Scott Manley is all over this.
Finally, and overall explainer on gamma ray bursts from Crash Course Astronomy.