2. Didn't this happen months ago?
Well, yeah. Technically it happened on Sept. 14, when the gravitational wave produced a "chirp" in LIGO's two facilities (more on that in a minute).
And almost immediately after the signal was detected, other physicists started spreading rumors about it. But the folks at LIGO were not having it.
With a scientific finding this huge, you want to be sure you're right before you go blabbing about it to the rest of the world. The LIGO team did their due diligence, and then some. They worked tirelessly for months to make sure the signal wasn't fake — and that there was very little chance of it being a random fluke.
Once they were confident, they wrote up their findings in a scientific paper with 1,004 individual authors.
Then that paper went through a process called peer review, which is a fancy way of saying that other, unrelated scientists looked at the data and signed off on LIGO's findings as being scientifically sound.
They didn't make their announcement until the paper was vouched for and accepted for publication. LIGO co-founder Kip Thorne told reporters that he didn't even share the news with his wife until a few days before.
3. But what is a gravitational wave?
Gravitational waves are the ripples in the pond of spacetime. The gravity of large objects warps space and time, or “spacetime” as physicists call it, the way a bowling ball changes the shape of a trampoline as it rolls around on it. Smaller objects will move differently as a result — like marbles spiraling toward a bowling-ball-sized dent in a trampoline instead of sitting on a flat surface.
Einstein actually proposed the existence of gravitational waves almost exactly 100 years ago when he presented his theory of general relativity.
Large objects should all produce gravitational waves, but big, violent collisions should produce the most powerful ones — and sure enough, the gravitational waves detected by LIGO are thought to have come from a collision between two black holes that occurred around 1.3 billion years ago and came to us at the speed of light.
4. Sooooo why do we care about that?
Up until now, we've only "seen" the universe with the electromagnetic spectrum — light. Not all of it is visible light, but even infrared, x-ray and radio telescopes are still using light to delve into the cosmos.
Gravitational waves basically add another sense to our arsenal. We're expanding beyond light waves for the first time.
This will be especially useful in studying dark objects, such as black holes: Gravitational waves don't care how dark an object is, so these dim objects will suddenly become "bright" in our night sky.
Furthermore, gravitational waves pass through matter without interacting with it. If you've ever seen someone stand in front of a spotlight, you know that light doesn't have that problem.
So think about it: Every time something big interacts with another big thing anywhere in the universe, these gravitational waves ripple out at the speed of light — and arrive at our doorstep completely unchanged by the matter they've had to pass through to get to us, ready for physicists to interpret their meaning.
5. Why now?
LIGO has been operating since 2002, so that's a fair question. Luckily, it has an easy answer: The facilities just got an upgrade. Their sensitivity has tripled, and it's going to keep getting higher in the coming months.
The detection happened basically as soon as the apparatuses were turned back on post-upgrade. They hadn't even officially reopened yet. It turns out that the signal detected was just below the threshold of detection before the upgrade happened.
That could mean that LIGO will detect these events super often in the future. The scientists are already combing through the data to look for more black hole collisions.
6. How the heck do you detect a gravitational wave?
The short answer is that you filter out as much noise as possible, then wait for really, really tiny movements to happen anyway.
This graphic is not a gif, but it's the best we can do:
The apparatus is so sensitive that if it were measuring the distance from the Earth to the Sun it could detect a change in width less than that of a human hair.
Here's the "chirp" detected by LIGO, converted to a frequency that human ears can hear:
7. What do we know about those colliding black holes?
This is our first direct evidence of binary black holes — a pair of them interacting and colliding.
The black holes were each about as wide as a metropolitan area. But incredible mass was packed into that tiny space: One of the two black holes had a mass about 36 times greater than our sun. The other registered at 29 solar masses. Both were rather massive as black holes go — 10 solar masses is more typical.
They orbited one another at a furious pace at the very end, speeding up to about 75 orbits per second — warping the space around them like a blender cranked to infinity — until finally the two black holes became one.
"The storm was brief — 20 milliseconds — very brief, but very powerful," Thorne said during Thursday's press conference. "The total power output during the collision was 50 times greater than all the power of all the stars in the universe put together."
8. What now?
It's true that the folks at LIGO got first dibs on gravitational waves. But that doesn't mean other folks will stop trying. In fact, there are other gravitational wave labs in the pipeline that haven't even opened yet.
Detecting gravitational waves is just the first step. Now scientists at LIGO are working with a true observatory, and they can get better and better at using gravitational waves to decipher the secrets of the universe. They're proud of themselves, and they should be, but they want other gravitational wave labs to step up to the plate. Because scientists may be competitive, but science is a team effort.