Deep in the woods in Livingston, Louisiana, the Laser Interferometer Gravitational-Wave Observatory (LIGO), detected a massive black hole collision. Although it only took less than a 10th of a second, it was the biggest ever merger of two black holes to date.
Joseph Giaime, head of the observatory, joined Louisiana Considered to talk to us about the event’s significance, and how federal budget cuts could impact his observatory.
This interview has been edited for length and clarity.
KAREN HENDERSON: Before we get into the weeds here, Joseph, let's break down some scientific terms. For those who haven't been in an astronomy class in a long time, what's a black hole and how exactly does this phenomenon occur in our universe?
JOSEPH GIAIME: The way gravity works is that space time is allowed to curve when there's, matter and energy present. And so if you put enough energy and matter all in one place, packed in tightly, space time can curve so much that nothing can escape from it. And so it's literally black in the sense that it doesn't glow and you can't really see it any other way other than by means of gravity.
When a star ends its life and stops glowing or its radiation decreases to the point where it can't support itself in gravity. If the star is big enough and it collapses, the core of the star becomes a black hole. It curves space so extremely 'cause it can't support itself and it gets smaller and smaller and smaller the only thing left is curvature in space time.
HENDERSON: So LIGO witnessed a black hole collision. Can you describe what that looked like and why this massive collision is so significant?
GIAIME: The waveform that we saw was indicative of two very, very heavy black holes, more than a hundred times the mass of the Sun each. And they merged together and made one that we think–there's a range, but we can't measure it exactly–but the range leads us to believe it's something bigger than 200 solar masses.
HENDERSON: How surprising was it to see two gigantic black holes collide and become a massive, even bigger black hole? And does the fact that this happened challenge any current theories on black holes?
GIAIME: It's a nice little mystery. Is it possible to build up a super massive black hole or something else that's big like that by means of these small ones merging together? That's one mystery. The other mystery is, when you have a very large star and it tries to make a black hole that's about a hundred solar masses big, there's a physics-y reason that makes that difficult to explain because there's an instability, a quantum mechanical instability that happens on its way to collapsing that would blow off so much matter into space that you wouldn't be able to make a black hole that size. So those two mysteries kind of come together in our wonderful observation. And that is a picture that kind of avoids both of those problems is that both of the progenitors, the two black holes that merged, were themselves second generation. So there were two other black holes that made one of them and, and another two black holes that made the other one. And then they found each other somehow. Those two other ones, those two new large black holes and then they merged together to make a 200.
So we both show that there's a path to making larger black holes from small black holes, and we also avoided the problem of that, of that instability because the instability wouldn't have happened if each of these two black holes had themselves come from more modest-sized black holes.
So we're still not sure you know about these questions. Only a few times have we seen black holes anywhere near as large as this. But it kind of shows that things can hang together that way.
And so you wonder, how could they possibly find each other? If they're the two that each combine into the first batch, well, they probably started life as a binary star. Most stars are binary stars, and so they were already close. But how did these other ones find each other? Well, one picture is that this is in the core of a galaxy somewhere where this happened, where there were lots close in, and so they interact gravitationally more often, and could have found each other. So it's pretty exciting to see.
HENDERSON: I'm sure a lot of people didn't even know that Livingston had this facility. How long has LIGO been around? And why was this wooded area of Livingston selected to be the site of this top-notch gravitational wave detector?
GIAIME: LIGO stands for Laser Interferometer Gravitation Wave Observatory.
We use light to measure the distance between isolated test masses across four kilometers. That is why it had to be someplace like the woods of Louisiana. We needed these very large, very flat areas where we could build vacuum tubes from which we've pumped all the air out and be able to measure things across two and a half miles of baseline in two different directions. And so when the NSF, and then MIT and Caltech together proposed to the National Science Foundation in 1989 to build two of these–and it was kind of an amazing time that was–they were able to get funding and we were able to break ground in both here in south Louisiana and in eastern Washington state, our sister site in 1995.
So the reason why Louisiana put in a proposal to get one of those sites is obviously because there was an LSU group here already doing something similar who knew all about it. And so that's what brought me to Louisiana. That's what brought Gabrielle Gonzalez, a colleague at LSU. She was actually the leader of the scientific collaboration at the time of our original discovery in 2015. The payoff back to the state for having inquired that way and making a proposal and providing the land, I think has been pretty high.
HENDERSON: Now Joseph, we can't talk about LIGO without talking about potential budget cuts. The observatory is in danger of being impacted by federal budget cuts. Can you tell us about the current budget proposal and, and how cuts to the National Science Foundation would impact your facility?
GIAIME: Right now the way LIGO is organized is we have two observatories, as I mentioned–one here, one in eastern Washington. And then there's two campus sites for the two kind of founding organizations that operate LIGO, MIT, and Caltech. We're a large facility and the NSF calls us a large facility, large infrastructure project that serves a community of researchers, all the people who are interested in our astrophysics and the people who are interested in improving our technology.
And so the budget draft that the administration produces every fiscal year–that's the way that the government works, has been working that way for a long time–that draft had us significantly reduced to the point where it would've been very difficult or it might be very difficult to run.
There was also a suggestion in there that we only operate one LIGO–more than a suggestion really. Now it's in the hands of the Congress to do their thing. You know, I'm not a political scientist, so if I started describing to you the process, all of your political scientists listeners would start laughing at me, but that process is underway. There have been signs that maybe there's hope of not having NSF and us reduced so much, and we're trying to get the word out that we're part of the community here and we think that we and the other NSF efforts are worth considering.
HENDERSON: What would you say to anyone who questions the usefulness of the observatory? What's your argument for LIGO maintaining all of its funds?
Let me tell you a very simple story to start the answer to that question. Most people, when they build a house, they put in windows. And it's not just for fresh air. People wanna know what's going on outside. And the grandest form of that is why astronomy and stargazing remains popular, even though most of us don't have an opportunity to go to those stars and they don't affect us much. So, people like to know what's going on in the universe, even the most extreme wonderful crazy things like the things we observe. That's one reason.
Another reason is, as I mentioned, LIGO’s technology is extremely bleeding edge for us to see such tiny effects. And so scientists and engineers and students who come through here and work with us and help us succeed, they get used to that. They get used to doing the impossible. They get used to saying, “How tiny of a thing can we see? How subtle of an effect can we observe?” They don't get scared away by that so much. When I give tours, sometimes I give tours to experienced scientists and engineers who aren't in our field, and I start describing how tiny the things are that we see and, and how small they are compared to normal kind of noise sources that people are used to in instrumentation. They start to look at me funny. Can this be true? Can they really be measuring something? 0.0001 the diameter of a proton across four kilometers, which is in fact what we do.
And we get past that. We put in decades of work to be able to get past that. And so the people who come through our programs move off into other areas of technology and industry and take that attitude with them. And I think it helps the country.
HENDERSON: Before we go, what comes next for black hole research or other research at LIGO? Following this merger discovery, what are you looking at next?
GIAIME: We intend to spend some amount of time improving the sensitivity. Our hope is to be able to look at some objects that we've seen before, like giant black hole mergers, and see them so precisely that we can start making limits on whether general relativity is actually completely right. And we hope to see more of an object that we've seen a few times, which is neutron star mergers, which can be seen by lots of astronomical observatories around the world. Everybody wants more of those. We've only seen one or two–only one that was seen around the world by other observatories. People want more of those, and we wanna improve our range so that we can see more of those together.