Kelly Holley-Bockelmann

Yeah.

Thanks.

It began about 20 years ago.

So we're about 20 years.

Right.

This has been going.

Yeah, it has been going.

We started off with the idea that, you know, the traditional metrics that that choose graduate talent are, you know, things like standardized test scores and grades and.

That'd be the GRE, right?

That's right, the GRE.

They select, you know, people who are really great at taking tests and very smart people.

But, you know, science isn't like that.

And so we need folks that have diversity of thought and background and who are creative to be able to tackle the big problems of today.

And so, you know, we designed metrics that search for that

that search for creativity and like you know, community mindedness and, and yeah, that those are the things that, that end up making scientists and in our mind.

That's not true.

I started, I've been director for, I think maybe 10 years, but, um, still a long time.

Got you.

LISA, which is the Laser Interferometer Space Antenna, is in space because it's tuned to look for things that are in a different mass range.

So, like, if you think of LIGO, the kinds of the things that it detects are massive.

massive black holes and and that are that are merging.

And it takes just that.

Right.

And that makes sense because the array, even though it's big, it's like four kilometers long for each of the arms.

And so like the wavelength of the gravitational wave kind of fits in that size.

And so if you want to detect things that are much more massive, you need really, really, really long arms and arms that are so long that they're bigger than the entire Earth.

You need to go into space.

No.

Yeah.

So the so Lisa is an interferometer that is that has arms that are like sort of in a triangle shape.

And the length between the two spacecraft, the arms are like twenty two point five million kilometers, which is like.

It is so big that if you were to put it around the sun, which don't do that because it's not a good idea.

But if you were to do that, the sun would fit right, right in it.

So it's like a square sized telescope.

Yeah, it's actually a misnomer that you even do that.

You definitely don't want to station keep.

You don't want to move these masses around at all.

What you want to do is let these test masses, that's what they're called.

They're roughly two kilogram gold and platinum cubes.

They are mapping spacetime.

So they are moving around in what is called geodesics or orbits that are going around the sun.

And naturally, they will map spacetime.

And you have three of them.

And so they are three independent orbits in a triangle that kind of tumble.

The way in which you detect gravitational waves is by looking for deviations from the lengths of the triangles.

And that is because a gravitational wave has passed by, not because you've oriented them or moved them in some way.

Yep.

That's the entire principle.

Yeah.

I think what you're saying is you want to make sure that you're always communicating between the three different nodes of the triangle.

Is that what you're asking?

Definitely want that to happen.

So you're always sending a laser beam from one part of the triangle, one little constellation piece to the other.

And that's what the LISA spacecraft is.

It's this constellation of three nodes and lasers shining between them.

Exactly what they're doing.

What you're doing is you're timing how long it takes to go from one node to the other and back again.

Yeah.

How do you even know that?

I'm sorry.

It's a very complicated bill.

But we have the mission has been adopted officially.

And what that means is that both ESA and NASA have decided this is a great, good idea.

We're going to put our resources toward it.

And it's supposed to launch in 2035, which sounds like a long way away, but it's not to build a whole spacecraft.

That's right.

It's your own space agency.

I'll say it again because I don't care.

Those black holes are the kind of black holes that are made from regular stellar evolution.

Like a star is born and then it dies and it has... Those are things are called stellar mass black holes.

And they're about 10 to maybe 100 times the mass of our sun.

And those are cool.

I, you know, whatever, but they're not my favorite.

The fit, my favorite are the kind that are, you know, millions of times more.

Yeah, that's right.

Well, massive, not super massive, but anyway.

Okay.

So wait, now back it up.

a massive black hole at the center that's maybe millions to billions of times the mass of our sun.

And we know galaxies grow by merging together.

And if each galaxy has a black hole in the center, then when the galaxies merge, presumably the two massive black holes merge too.

Not 100% guaranteed, but that's the research I do.

I use supercomputer simulations to figure out how long that process takes and what kinds of changes that makes to the galaxy that it lives in.

So I study the time scales over which that happens.

Well, yes and no.

I would personally be SOL on that science topic.

But, so I'll come back to the answer to your question here, but I want to make sure that y'all know that LISA would still be great, even if it would not detect any of the massive black holes.

And that is because as soon as LISA turns on, you're going to be able to detect black

All of the individual stellar mass black hole binaries and neutron-style binaries and white dwarf binaries, there's supposedly 10 million of these in our Milky Way.

Exactly.

Exactly.

So by making something as big as Lisa, you're catching...

all of the sources that are loud and orbiting around one another on time scales of an hour.

And there's a lot of astrophysics that does that.

Like, yes, there's these massive black holes that I love when they're colliding, but also these individual stellar compact object binaries is what they're called.

There's even these things that are called EMRIs, extreme mass ratio in spirals.

And that is one massive black hole, but then little black holes orbiting around each other.

They take a million years to do that.

Oh, wow.

And so they're like orbiting around this.

Sorry, everybody.

But they're orbiting around this massive black hole.

The neat thing is that it traces space-time, like, all over the place.

The orbits are beautiful.

I wish that you could see them, and I wish that we will see them when we sleep.

You are precisely right.

The wonderful thing about Lisa is that it's opening this new window into the universe.

And every single time we open a new window in the universe, we discover something we've never expected.

And so I can tell you all day about what we think we'll detect.

And for sure, we think we're going to detect some stuff.

But the most exciting thing is that there's going to be something that we don't know that is in that window.

I can't wait.

They are – I like – well, they're called test masses, and I like to think of them as they are the things that are probing the space-time, meaning that their orbits and where exactly they are in space and time, they're the things that the lasers are measuring the distance between.

This is why y'all get paid the big bucks.

They're the rubber duckies.

They're super expensive and gorgeous rubber duckies.

I'm with you.

When I was new to this, I thought I was going to be brilliant and tell everybody, why not a sphere?

And someone took me aside and said, you can't machine spheres to the precision that you need a

a cube.

And so I, I trust them.

This has been something that folks have been thinking about for, for, you know, a generation for 50 years now.

There are other designs.

In fact, there are plans for a Chinese gravitational wave mission that does use forearms.

That's right.

And so if you have three and you lose one, you still have two.

So you would still have a gravitational wave mission.

I think this is just one of those instances where you have a cost benefit analysis and, you know, it would be more expensive with four or five.

So so three is kind of the ideal configuration.

No.

It's not just that, right?

There's more to it than that.

That's that is correct.

And so there's very sophisticated interferometry you have to have.

And you do have to have some things as as much as like, for example, if there were a solar windstorm, you get these you get charges that are on the the test mask.

And that can cause it to drift electrostatically a little bit.

Well, that's not a gravitational wave.

You need to have some way to discharge that.

And so there's special LED discharging mechanisms that have been invented by by folks in the U.S.

to be able to.

For this purpose.

For exactly this purpose.

Yeah.

Look at that.

USA.

Absolutely.

I mean, it ends up being, you know, not only that, but individual parts in this constellation, you have to weigh each object that you put in, each little cable very, very, very distinctly because that causes a gravity gradient.

And that's going to, you know, mimic a gravitational wave.

is what you're saying.

Yeah.

Yeah.

Unless you screw, there's another thing that that's called tilt to link coupling where like, just like you said, you have it when you have a cube and there's a little bit of radiation pressure, which is going to put a little force, it's going to twerk it.

And so you'll get this cube rotating back and forth.

And that difference is going to be, it's going to mimic a difference in the path length because you're going to hit it, not perpendicularly.

And so this, you know, bobbing back and forth is, is something that you have to correct for.

Yeah.

Y'all make a good team.

Okay.

So yes, we do have to have things that are that relatively precise.

So we aren't detecting things a fraction of a proton length, not detecting relative changes on that scale.

But that's only because our constellation is so big.

So we're just detecting changes one part in 10 to the minus 20 because that's how strong the gravitational waves are.

But because the mirrors are separated by such a huge distance, then the differential scale ends up being bigger.

Right.

The other thing is that many of these massive black holes, when they merge, they're so loud.

And so the kinds of signals that we're going to get are having signal-to-noise ratios of thousands.

Wow.

he's not wrong in that these, these are really, really loud signals.

And so you, your, your instrument just has to work and then you'll definitely catch the, you know, the gravitational wave signal, but you have to get up there.

And it takes a while to, to build the instrument to get up there.

And I'm trying not to cry right now, y'all.

Yeah, I'm going to turn serious now because that's actually happening.

You know, the latest president's budget request has zeroed out, Lisa.

And so we are a partnership with ESA and NASA.

NASA is a junior partner.

And...

The U.S., if this request goes through, the U.S.

can no longer participate and give our technology to this mission.

You're totally right.

Sorry, I interrupted you.

But like...

As a scientist, I'm glad there's two other Chinese gravitational wave observatories that mimic LISA because that means there's more probability that this science that I love will actually happen.

But we are losing out.

We're not going to be able to have the technological know-how.

We're not going to have the stable of people who can solve big problems.

And so we lose out.

And that sucks for us.

Yeah.

I get it.

I also think it's just, and I think I'm echoing some of the things that y'all, y'all are saying too.

It's just that the act of building this humanity scale system,

scientific endeavor, the act that we're participating in that trains us, trains our, you know, it allows us to have a pool of people who are prepared to tackle the next challenge.

I was just talking with a friend the other day who said, you know, there's always these disaster movies.

And then somebody, you know, comes and says, let's get us a scientist to solve all the problems.

And it's usually somebody from NASA that comes to like save all, save, save the earth.

But we won't have those people.

if we are not participating in these, you know, big challenges.

Yeah, I think that's great.

I personally am excited about the gravitational wave aspects, but there's a lot of technology that can be used for the efforts for things like the Moon to Mars effort.

So needing to know exactly where we are is GPS.

And so LISA is really going to be developing that technology.

The communication, laser communication, is going to be something that we'll need to have prepared.

And so all of these technological pieces, which have nothing to do with gravitational waves, are being developed and will be really useful for things that are our nation's priorities.

No, really, GPS is not going to be sufficient for where we need to go in the future.

And Lisa really helps us get there.

I'm sure there's probably an acronym, but if not, I will ask my friends.

So actually, I have a friend right across from the hall from me at work who is part of the effort to do to nanograph, which is this pulsar timing array.

And one of the things he specialized in was recognizing that the pulsars, when you timed them, they gave you there.

You needed to know where you were in the solar system.

So what is called the solar system barycenter.

You needed to know your position in the solar system really, really well.

And so far, we calculated it wrong.

And so that had added a big error to whatever they were calculating.

And so that Pulsar stuff helped us understand our place in the solar system.

Our own place in the solar system.

Our own place, right.

Well, right now we are the junior partner to ESA.

And for those of you who are concerned that Lisa would not go without us, ESA is fully prepared to be able to go on with the mission without the U.S.

participation.

before gravitational waves were detected.

There was another funding snafu and NASA pulled out of LISA again.

And so ESA was left stranded.

So by now we had broken up with them once and ESA said, you know, we're going to have a contingency plan.

And so now we could well be breaking up with them again.

And there has been talk about

whether or not they would let us back, which I, you know, personally, I don't know if I blame them.

We've broken up with them.

Yeah.

Yeah.

I will do my best.

I always think of it like a light race.

And so in an interferometer, you will often, like LIGO, for example, you will shine a laser from one part of an instrument to another and have it bounce back.

And same for the other direction, you will laser in another direction, have it bounce back.

And if the time it takes to go from one side of the arm to another is exactly the same, then the light will interfere with each other.

And that's where the interferometer part comes in.

When the light interferes with each other, they cancel each other out and you see no signal.

But if the arm lengths are a little bit different, then it takes a little bit more or less time to go along one arm.

And so by the time the light gets back, the light doesn't perfectly interfere anymore and you get to see a little bit of light still left over.

And so that's kind of how an interferometer works.

It's a light risk.

I think it's it's like how we we share knowledge and build on on one another and how the nature of, like you said, of collaborating and really working towards something bigger than than we knew before.

Yes.

No, bits and pieces of it are being built by by different nations and we all put it together.

So, for example, the U.S.

is responsible for the laser, the discharge management system that I talked about and the telescope.

Yes.

Um, which one there are telescopes that, that are actually made out of glass.

It's a very, very, uh, temperature stable glass called zero door and it's translucent.

Um, and so if you kind of, which I think is really cool, there's a picture of it where you can, where there's like a test model right now and they shine a light underneath it.

So it glows really, really well.

You're exactly right.

The whole name of the game for LISA is to keep everything as still as possible.

Extra charges, even air that would be left over in the instrument.

Sometimes there's this outgassing that you do to get rid of all the air in a space instrument, but individual air molecules hitting that test mass will fake a gravitational, it'll make it move.

It'll make that test mass move and make it seem like a gravitational wave.

Wow, it's left over from the... Left over.

Yeah, that's what happened.

Absolutely.

That's that oxygassing stuff that we were just talking about.

In fact, sorry, story time.

As I said, you need to keep the instrument as stable as possible.

And there was a big, like, how are you actually going to make LISA?

You need to have, you know, what about solar wind?

Could that push the test mass, et cetera?

So there was this Pathfinder mission called LISA Pathfinder.

And its only job, its only job was to say, how still can we hold that test mass into space?

And it performed exquisitely, like a thousand times better than it was expected to perform.

And when you look at, you know, the tiny fluctuations in the test mass way afterwards, the tiny fluctuations were.

were caused by individual air molecules hitting that test mass.

Because they didn't outgas, they thought, ah, we don't really need to be this accurate, so we won't outgas as well as we thought.

But heck yeah, individual air molecules.

the constellation is a big enclosure for that test mass and so it will react and move in such a way to like counteract the solar wind motion but keep that test mass still

Wow.

Yeah.

Absolutely.

There's radiation pressure as well.

And so, you know, you build the instrument with, you know, with the ability to compensate for that fact of known radiation pressure.

If dark matter were primordial black holes and if some of them were to merge or even be close enough so that they're orbiting on, you know, a half hour, hour time scales, they will be observable with LISA.

So I've been working on predictions for what the LISA's signature would be of these primordial black holes.

And yeah, definitely if they're there, LISA would detect them.

Definitely the second.

I cannot be wrong.

That's the coolest part.

Say that out loud.

cannot wait to be wrong though that is the best part is like there's gonna be something like like for example when right before uh the discovery of uh not discovery the detection of of gravitational waves with LIGO if you asked any astrophysicist what is the mass of a of a stellar mass black hole they say 10 solar masses I have

I, in grad school, had tests and I wrote 10 solar masses.

And if I didn't, I would be wrong because they would mark you off.

What did what did LIGO detect?

30 solar mass black holes.

And so immediately afterwards, all the astrophysicists were like, how do we make these black holes?

I don't know.

They went back to their drawing board and we learned a whole bunch of really cool stuff.

That's going to happen when Lisa launches and it's going to be the best thing.

It's going to make us all wrong.

Absolutely.

And that kind of goes back to the FISC program.

We search for folks who will be comfortable and excited about not always getting the right answer.

I think that makes the best scientists.

Something like that.

Something along those lines.

We have a website called SaveLisa.org, and it tells you exactly how you contact your rep.

Thank you.