Read on for our brief summary of today's press conference:
- For the first time ever, scientists have detected gravitational waves coming from the collision between two neutron stars.
- LIGO/Virgo detections of gravitational waves were paired with a gamma ray burst, which led to the first-ever detection of a binary neutron star collision.
- This is the first direct evidence that gamma ray bursts can be caused by colliding neutron stars.
- Because it was detected so quickly, optical telescopes were able to point at the location of the collision - and capture images of it across the entire electromagnetic spectrum.
- For the first time, we have gravitational wave and electromagnetic wave detections of the same event!
- The electromagnetic waves and gravitational waves arrived at Earth at the same time - meaning that for the first time, we have confirmation that gravitational waves travel at the speed of light.
- Analysis of the electromagnetic data has confirmed for the first time ever that heavy elements such as gold, platinum and uranium originate in neutron star collisions.
- Finally, the combination of the gravitational waves and the redshift of host galaxy NGC 4993 could be combined to measure the age of the universe - and it was remarkably close to our current best estimates.
- A lot of questions were answered and mysteries solved, but the event raised new questions too - there's a lot more work for multi-messenger astronomy ahead!
Make sure to check our in-depth article here to learn more about how it happened and about the massive implications this historical discovery has for physics and astronomy.
You can read our live blog coverage of the announcement below:
9:30am EDT: It's 0:30am here in Sydney, Australia, so we're basically running on coffee and excitement. But it's always fun to stay awake for these announcements - and this one's going to be so worth it!
The big press conference at the National Press Club in Washington DC is starting in 30 minutes. We'll embed a live stream link down below as it gets closer!
9:31am EDT: While we wait for the announcement in less than half an hour, let's run a refresher course to entertain ourselves and prepare for the big news.
Gravitational waves are a lot like waves in water, or soundwaves in the air, except they're rippling across spacetime. When a massive event happens - like two black holes colliding - it's like dropping a stone into a puddle.
Ripples race out across the universe in all directions at the speed, theoretically at least, of light.
9:35 EDT: In all our excitement we forgot to mention that you should keep refreshing this page to get the latest updates! (Also, sorry in advance for any egregious typos. We made popcorn to celebrate and it's getting in the keyboard.)
9:37 EDT: Gravitational wave astronomy is still extremely fresh! We only got the first ever confirmation that gravitational waves exist last year, in February 2016.
It was one of the biggest astrophysical discoveries in the previous hundred years, and may remain that way for another hundred. It's a huge deal - confirming predictions Einstein made in his theory of general relativity 100 years earlier in 1916.
9:40 EDT: T minus 20 minutes! Hang on, we're getting the live stream link verrry shortly.
Meanwhile, a bit more trivia: three of the scientists behind the discovery were just awarded the Nobel Prize in Physics earlier this month. Rainer Weiss of MIT and Barry C. Barish and Kip S. Thorne of CalTech represented over 1,000 scientists who participated in the discovery.
Today, over 1,200 and around 100 institutions around the world participate in the LIGO Scientific Collaboration.
9:43 EDT: Let's talk more about the science! Here's how the gravitational wave detectors work:
LIGO's detectors are known as Michelson interferometers. A laser beam is shone at a mirror down. This splits the beam. Part continues going forward; part splits off to the side. They're bounced off mirrors on the other side, and meet back in the middle, cancelling each other out. This meeting is called interference.
If the arms change length, as they do when a gravitational wave hits, one beam will take longer to travel back to the middle and the two beams won't cancel each other out. The resulting light continues on and is picked up by a photodetector.
LIGO's interferometers are the largest in the world, with arms 4 kilometres (2.5 miles) long.
9:45am EDT: The music just started on the livestream! We're embedding it at the bottom of this article so we can all watch together.
9:50am EDT: 10 minutes to go! We're loving this jazz.
9:52am EDT: This new gravitational wave astronomy has progressed amazingly fast, by the way.
Until earlier this year, only the two detectors were operational. This meant that scientists could only pinpoint gravitational wave events to a very broad swathe of sky.
But in August a third detector was added - Advanced Virgo. This allows triangulation. Gravitational waves don't hit every detector simultaneously. The order in which detections occur, and the length between them, lets scientists calculate the location with much more accuracy.
It was this third detector that showed a much smaller area for the fourth gravitational wave event.
9:55am EDT: FIVE MINUTES! The music is getting more groovy!
9:57am EDT: Okay, we're only a few minutes out, time to address some rumours.
That fourth gravitational wave event was a huge deal - but it wasn't what we were expecting. In August, University of Texas astrophysicist J. Craig Wheeler tweeted out that there was a new LIGO detection with optical counterpart.
As in, something we could actually see to go along with the gravitational wave detection.
Greater accuracy is fantastic - but what did Wheeler mean? Did he get something wrong? Or was there another announcement to come…? WILL OUR SOX GET BLOWN OFF?
9:59am EDT: Oooookay, we are hearing mike checks! Here is the speaker list for the first announcement:
* France Córdova, Director of the National Science Foundation
* David Reitze, Executive Director, LIGO Laboratory/Caltech
* David Shoemaker, Spokesperson, LIGO Scientific Collaboration/MIT
* Jo van den Brand, Spokesperson, Virgo Collaboration/Nikhef, VU University Amsterdam
* Julie McEnery, Fermi Project Scientist, NASA's Goddard Space Flight Center
* Marica Branchesi, Virgo Collaboration/Gran Sasso Science Institute, Italy
* Vicky Kalogera, Astrophysicist, LIGO Scientific Collaboration/Northwestern University
10:00am EDT: France Córdova is on. Hold on to your hats, everyone.
10:03am EDT: "Today we are thrilled to announce that scientists have detected gravitational waves coming from the collision between two neutron stars."
10:03am EDT: We detect a tremble in her voice. We are pretty emotional here ourselves over at ScienceAlert.
Scientists were also able to detect LIGHT! For the first time, we have gravitational waves and electromagnetic waves (light) from the SAME EVENT.
"Well, Dave, we did it again."
10:03am EDT: Read more about this discovery right here.
10:05 am EDT: David Reitze: "We have for the first time seen gravitational waves and light from the collision between two dense, dense stars."
LIGO and Advanced Virgo detected the signal at around the same time, and determined it was from neutron stars 130 million light-years away - that's 130 million years ago.
But the most amazing thing? The emission of light. Seven space-based observatories and every continent on the planet turned telescopes to capture it.
10:07am EDT: LIGO just tweeted this map of detections:
10:09am EDT: Astronomers have thought for a long time that heavy elements such as platinum, gold and uranium are created in the collisions between neutron stars.
Now, we have actual concrete evidence of that. So the gold on Earth probably came from neutron star collisions, Reitze says. Even the gold in his grandfather's pocket watch. Awww.
10:10am EDT: David Shoemaker is now telling us about how gravitational waves are measured. The distance the arms move is less than the width of a human hair - that's how sensitive this equipment is.
The length of the inteferometers' arms boosts the signal over distance so that it can be detected. If you're interested in how this works, you should watch this section of the livestream, it's really fascinating.
We've explained it a little above, but Shoemaker is the expert (obviously).
10:15am EDT: "We shared in the joy and excitement of that moment." WE ARE FEELING IT NOW.
The "chirp" signal from the neutron star collision (GW170817) was longer than the chirps from black holes because they're much lighter.
Also, at the same time as the gravitational wave signal came through, a gamma ray burst - caused only by the universe's most violent events - came from the same region of the sky!
That's how the team knew they were onto something different.
10:17am EDT: Jo van den Brand from the Virgo Collaboration has taken the podium. The gravitational wave signal arrived at Virgo in Italy first, then LIGO's two detectors, a few seconds apart.
This is how they figured out where to look for GW170817, in the constellation of Hydra, near galaxy NGC 4993.
The illustration in this tweet shows how they detected it:
"It's the start of a beautiful new field in science."
10:23am EDT: Ooooh we're getting into the gamma ray burst part!
10:22am EDT: Julie McEnery works on the Fermi Gamma-Ray Telescope that made the first detections of those gamma ray bursts (along with the ESO's INTEgral gamma-ray burst telescope) that coincided with the gravitational wave detection.
Initially, she said, they didn't think anything of it - until half an hour later, when an email came in, alerting the Fermi team to LIGO-Virgo's detection.
"With these observations, we're not just learning what happens when two neutron stars collide. We're also learning something fundamental about the nature of the universe."
10:27am EDT: Here's why you might hear Albert Einstein mentioned in connection with this new discovery. In 1915 he predicted that the speed of gravitational waves would be the same as the speed of light.
And because the gamma rays and the gravitational rays arrived at the same time, it confirms that gravitational waves do indeed move at the speed of light.
In other words, Einstein nailed it.
10:28am EDT: Marica Branchesi is showing us what happened in the days following the gamma ray detection.
The electromagnetic emissions changed from very bright gamma rays, to X-rays, to ultraviolet, to infrared, to radio waves. You can actually see that in this timelapse.
10:31am EDT: WOW, take a look at this:
10:32am EDT: LIGO's Vicky Kalogera is here to explain to us the history of these two neutron stars. She says that neutron stars act a bit like lighthouses, with their polar jets pulsing as they rotate.
This has led to them being mistaken for pulsars - the first binary neutron star wasn't discovered until 1974.
These stars are very far apart - over five times the distance between the Earth and the moon - and will not merge for another 300 million years.
10:36am EDT: The two neutron stars in GW170817 lived a very long and happy life, but their orbit inside their galaxy changed when the second star collapsed into a neutron star.
Kalogera describes it as taking a holiday in their twilight years - that's rather poetic and makes us happy.
"We've solved a lot of mysteries, but at the same time, we've opened up a lot of questions. We're hoping that future observations .. are going to answer a lot of those questions."
10:38am EDT: The future of gravitational wave astronomy is looking "golden bright", thank you for that pun.
10:42am EDT: Okay guys, this announcement is wrapping up now and we're in the Q&A phase, so we're just doing a quick recap now to wrap up this live blog as well.
10:50am EDT: If you're keen to keep watching, there will be a second panel at 11:15am starring several supernova experts, diving deeper into the incredible science we're learning from this discovery.
10:58am EDT: And that's all from us tonight! Thanks so much to everyone who tuned in! We'll be buzzing for days and yes, it was absolutely worth staying up so late for this - after all, such historical moments don't come around that often.
The livestream from the event is here: