Vicky Kalogera is Thrilled by the Extraordinary
A senior astrophysicist at the LIGO Scientific Collaboration and Daniel I. Linzer Distinguished University Professor at Northwestern, Kalogera digs into why she keeps coming back to astrophysics, after more than three decades in astronomy.
By: Katie Liu
The universe chirped on a Monday.
The first indication that astronomical history had been made came in the form of emails piling in Dr. Vicky Kalogera’s inbox. Kalogera, a professor of physics and astronomy at Northwestern, was also a leading astrophysicist of an international group of scientists known as the Laser Interferometer Gravitational Wave Observatory (LIGO) Scientific Collaboration. They were chasing after an elusive aftereffect of colliding black holes and dead stars, known as gravitational waves. Albert Einstein predicted their existence over a century ago, but such phenomena were long thought impossible to detect.
It was September 14, 2015. LIGO detectors had just turned on following several years of instrument upgrades and renovations. That Monday was also packed for Kalogera, as she juggled hours of back-to-back meetings.
Communication zipped back and forth as she checked her phone every now and then. There was something about a signal. Kalogera was convinced, however, it had to be yet another system test – extra insurance to check that the detectors were working properly. With that in mind, she went on to pick up her then-three-year-old from daycare and headed home.
As she was setting up dinner, one of her graduate students pinged her with a text.
“Have you looked at our emails today?”
Yes, Kalogera replied, she had. “Are we testing? Is this a signal? What are we doing?”
“We got a signal.”
No way, she thought.
It wasn’t a denial out of awe, but practicality. The observing run was just about to begin. It could not possibly be an actual detection.
Over a Skype call later that night, she and her student ran over the codes responsible for analyzing LIGO data. The measurements looked real enough, both clean and beautiful.
“‘I’m so happy, your code is working so well. We’re ready for the observing run – but there’s no way this is a real signal. It must be a test,’” she recalls telling him, laughing now. “‘Now, don’t spend the whole night up. Go to bed, and we’ll talk tomorrow.’”
The days and weeks following the signal consisted of hours upon hours of work, simulations, and flurries of teleconferences with the hundreds of collaboration members around the world. All the analysis and consulting across teams and near 24/7 effort was with one thing in mind: check everything that could possibly be checked.
Eventually, they proved what the world now knows. On that day in September, for the first time, humans detected gravitational waves, the remnants of the cosmic catastrophe of two black holes colliding to form a bigger one. What Kalogera had dedicated years of her life to studying and analyzing, and what Einstein had predicted exactly 100 years ago at the time, was finally confirmed.
The first detection was only the beginning. Later in 2015, two other signals followed, one about a month later in October and the other the day after Christmas. As each new detection widened our vision of the universe, it also flung open the door to new questions.
“It answers the question, do they exist? Yes. That question, answered. But now that we have one, we can start saying: How many more? What masses? How far away?” Kalogera asks. “This one source, we cannot answer. But what about the whole population out there?”
Almost eight years later, the LIGO Scientific Collaboration, alongside its sister, the Virgo Collaboration in Europe, and the Kamioka Gravitational Wave Detector (KAGRA) in Japan, began its fourth observing run on May 24, 2023. The initial discovery did not only prove Einstein right, but also birthed a new frontier in astrophysics, gravitational wave astronomy. Kalogera, who joined the LIGO collaboration in 1999, has been at the forefront of its coming-of-age.
Kalogera has loved astronomy since her undergraduate years in Greece. She has spent more than 30 years studying and learning about the cosmos, looking after the unseeable objects churning in the distant neighborhoods of the universe. Breakthroughs like the first detection of gravitational waves, though, aren’t what keeps her coming back after all this time. What’s really extraordinary to Kalogera is the labor of love lying in between: finding one answer, then two more questions.
***
Gravitational waves, essentially, are ripples. If the universe is situated upon the fabric of space and time, one which sags beneath the mass of cosmic objects and curves to tip them into orbit around one another, then the collisions of certain astronomical objects would disturb that fabric, creating waves on the surface, like stones on water.
Usually, such undulations are so small they are virtually immeasurable. Sometimes, however, events can be cataclysmic enough to cause ripples in spacetime, strong enough that detectors on Earth can sense them. A pair of black holes, also known as a binary system, can begin to spiral toward one another, gradually accelerating. Eventually, the pair will meet in the middle to merge into a new and bigger black hole. The same can occur for pairs of neutron stars, or even a neutron star and a black hole.
Each cosmic waltz sends out different signals. But if astrophysicists manage to detect the gravitational waves sent out from the two slow dancers, they can figure out details such as how massive the partners were, how quickly they were rotating, and where in the sky they came from.
The way gravitational wave astronomy has burgeoned in the recent decade is comparable to the first discovery of exoplanets, says Shane Larson, professor of physics and astronomy at Northwestern and one of Kalogera’s longtime colleagues. When Larson was in college, the only known planets were the ones in our own solar system. “Even Pluto was a planet then, as I like to remind people,” he says jokingly to me over Zoom. Yet, generations born after Larson can grow up in an era of picture proof that the universe, as far as anyone can tell, is scattered with planets and galaxies and stars.
“That’s an equally huge change in the way astronomers think and do science, because exoplanet science didn’t exist 20 years ago. It does now,” Larson says. “Gravitational wave astronomy is the same way. It didn’t exist 20 years ago, but it does now.”
In the U.S, there are two LIGO sites, one in Hanford, Washington, and the other in Livingston, Louisiana. The two work in tandem to catch signals as they pass; if a wave hits one detector, then it will pass through the other. “The detector says, ‘Oh, I saw something.’ It writes it down in the log, and then it asks the other detector, ‘Did you see something, too, at the right time?’” Larson explains. “If it does, then it’s like, ‘Woah, this could be important. Let us tell the humans.’”
To envision the LIGO detectors, simply hold up both of your hands with your fingers in an L-shape. Imagine your index finger and thumb represent LIGO’s four kilometer-long arms, about as long, if not longer, than an average airport runway. The detectors use a technique called laser interferometry to sense gravitational waves. In the center point where LIGO’s arms join, a laser splits down each hollow, airless tube. Mirrors at the ends of these arms reflect the light back into the center point. Because light is a wave, it has peaks and troughs. When the two beams of light meet again in the middle of the detector, those mountains and valleys usually anti-align, canceling out the other. This way, no light will appear.
What scientists are measuring is the time it takes for the laser light to go down and up each arm. And since light always moves at the same speed, it’s one of the most accurate rulers that scientists can use.
If in some distant part of the universe, a collision of compact objects sent gravitational waves hurtling outward, they’ll shake up space and time. On Earth, one of LIGO’s arms will stretch, and the other will squeeze. Therefore, on one end, light will have to take longer to travel back home, while in the other, it’ll arrive early. At this point, the peaks and troughs of the waves will no longer be in anti-alignment. Some light will show in the detector, indicating a gravitational wave has passed through.
The time it takes for the laser to go back and forth, with this stretching and squeezing, is related to the properties of the gravitational wave, according to Larson. He compares it to putting on a sock. When you hold up a sock, it rests in a certain shape. If you imagine an ant walking around that sock, then, it would take a certain amount of steps to get around the perimeter. But when you put on a sock, the fabric stretches around your foot; the ant will have to take a longer time to finish its journey. Depending on who’s wearing the sock, the ant might take a certain number of steps – similar to how one black hole merger might make a certain stretching and squeezing pattern, while a neutron star merger would make another.
“Think of the sock like LIGO,” Larson says. “Your foot’s the gravitational wave, and the ant walking around your foot is the laser light.”
Besides the kind of source the gravitational wave came from, scientists can also figure out how massive its original sources were and where they were in the sky.
LIGO is not a telescope, but more like an extremely sensitive microphone. It listens and records noises from all kinds of sources that might move the ground: distant earthquake rumbles, a car passing by, black holes colliding.
What do you actually hear when a gravitational wave is converted into a sound?
“If it’s a loud enough gravitational wave signal, you’ll hear this noise which sounds kind of like static,” says Ben Farr, a member of the LIGO collaboration and assistant professor at University of Oregon. “And then on top of that, you’ll hear a really faint chirp. A little whoop!”
(To me, it sounds almost like a raindrop falling back into the sea.)
***
Kalogera was the first traditional astronomer to join the LIGO collaboration, but her career started in the classroom as a physics major in college. She grew up in a small town in Greece and got her high school and college education there, too, at the University of Thessaloniki. As a high schooler, she would read about astronomy every now and then, but she pinpoints the first step of her journey to be the entry-level astronomy class she took her freshman year.
“The feeling was really like falling in love,” she tells me as we sit in a sunny corner of her office. Smile lines crease the corners of her eyes now as she holds her glasses in one hand.
After that class, astronomy was all she wanted to talk about. Reading consumed her time, as did her local observatory. By the next year, she had already decided her Ph.D. would be in astrophysics. The star of her future thesis, done at the University of Illinois at Urbana-Champaign, would be one of the universe’s densest objects, neutron stars.
When a massive star dies, there are a few possible endings in store for it. Neutron stars are the remnants of giants that burnt out and collapsed, but were not massive enough to completely transform into the light-devouring black holes which fascinate scientists and movie-makers alike. Instead, the cores of neutron stars combine positively and negatively charged particles, protons and electrons, to form neutrons, resulting in dense objects about as massive as the sun.
Kalogera’s specialty initially focused on these objects in binaries and the X-rays they emit, a field otherwise known as X-ray astrophysics. She would not come to gravitational wave astronomy until her later years as a postdoctoral fellow at Harvard University, when a professor invited her to attend a conference on such elusive waves.
“It was all kind of almost coincidental,” she says.
In the late 1990s, the field of gravitational wave astronomy was not well-established. Efforts to observe them were more of a fledgling offshoot of the astronomy community. It was different from trying to track light or radiation from the universe. It was, essentially, an experiment in detecting the invisible.
At the time, the initial LIGO detectors were wrapping up years of construction. Scientists in the collaboration, who Kalogera met at the conference, eventually invited her to become a member.
“At the time, I didn’t have a long-term position in the field. When I talked to my astronomy mentors, they all told me, ‘This is very dangerous, really, we’re not going to have any detection. This is a dream,’” Kalogera says. “‘We’ll never actually observe anything.’”
But there was just something about that work. “I did join the collaboration,” she says, “because I was really enamored with the idea – the dream – of detecting gravitational waves.”
Kalogera made a compromise. Though she joined LIGO, she also decided to continue with X-ray astrophysics (“Lots of problems there, lots of research,” she says). Even now, her expertise spans a broad spectrum, including neutron stars, black holes, white dwarfs, data analysis, and star simulations. But she added one more item to her roster too: proving Einstein right.
***
When picturing historic days in astronomy, you may think of the first moon landing. You might envision the grainy figure of Neil Armstrong, unrecognizable beneath his white, chunky suit, taking one small step, but a giant leap for mankind. The discovery of gravitational waves is another one of those moments – this time, in our own lifetimes.
But the hours following LIGO’s first detection were almost mundane. Kalogera was in Northwestern’s Technological Institute, a place where STEM majors congregate for classes or get lost in the endless hallways. Larson was standing among moving boxes, preparing to finally settle into his new house, when Kalogera texted him about the signal.
From then on, Larson says, it was a matter of convincing themselves it was real.
“I can remember sitting there with Vicky in conference rooms all the time, and some days she’d think it was real, and some days she’d think it’s not real,” he says. “It was just driving us bonkers, because we couldn’t convince ourselves that it was real or not.”
The work to analyze the first signal, checking and rechecking everyone’s findings, was constant, both within Kalogera’s research group and LIGO-Virgo collaborators as a whole.
“We were sleeping, but it felt like now it was consuming every free minute of our time,” she says. “Everything else that I could postpone or neglect, we were postponing and neglecting.”
To analyze just a single wave, and convince the hundreds of members of the international LIGO-Virgo community that it was real, took months. (Though the initial signal was found with LIGO detectors, it was the people from both collaborations who ultimately made the discovery together, Kalogera says.)
Part of the doubt also came from previous rehearsal runs, known as blind injections. Should a detection occur, there was a chance that it was a fake one simulated by computers. Scientists would not know if or when one was going to occur, and if one did, they didn’t know what kind of binary it simulated. The test was to ensure astronomers would be able to handle a real gravitational wave signal if it came through, according to Farr, Kalogera’s graduate student who had Skyped with her the night of September 14.
One such test had occurred in 2010, Farr recalls, where scientists were convinced that they’d found a detection, to the point of writing and preparing to send off a paper to a physics journal. “We opened up the envelope and it said, ‘Haha, fooled you,’” Larson says.
But Kalogera recalls she began thinking they might be onto something big about a few days in. What truly tipped her over was when a second signal came through, on October 12. The binary black hole masses, distance from Earth, and spot where they collided in the sky were all different.
Things were working exactly as they should, the second blip confirmed.
“We’re opening this brand new field,” she says she thought. “Gravitational wave astronomy is here.”
When Kalogera tells me about the moment of finally confirming September’s sightings, she remembers hundreds upon hundreds of collaborators piled onto a telecon – more than the servers could handle, crashing it at first. After some finagling from IT and a second try at the call, she and other scientists gathered to prepare for the global analysis of their signal.
Up until then, after all their weeks of work, they had been relatively sure about what they had detected. Yet, there was still that nagging possibility that it wouldn’t be there. The indication of the signal’s veracity came in the form of a data plot. When the plot flashed on the screen, among all the other points in it forming the layer of noise artifacts collected by the detectors, Kalogera says, one stuck out above the rest.
That was their detection.
At the sight of that single point, Kalogera remembers feeling pure relief.
“It is like we thought it would be,” she says.
The lead paper announcing their findings was written by a small team of about 20 people, though it had the input and voices of hundreds in the broader collaboration. Addressing every single comment and question, mulling over every word, and debating every sentence, before sending it around the community for feedback and review, was a process that took weeks.
“It felt like we were writing the most significant publication we would ever write in our life,” Kalogera says.
The rest of the world came to know what the LIGO-Virgo collaborators discovered on February 11, 2016.
“Once we knew it was real, then it really started to sink in. ‘Wow, this is really it,’” Larson says. “Tomorrow, when we wake up and the world knows, astronomy is going to be different forever.”
***
When I first meet Kalogera, it’s in her office on the eighth floor of a tall building, with walls made of semi-circular glass. It’s the structure overlooking downtown Evanston, about a five minute walk from Northwestern’s south campus and an even shorter walk from the nearby Starbucks. This floor houses the Center for Interdisciplinary Exploration and Research in Astrophysics, or CIERA, one of Northwestern’s many research centers.
Kalogera’s in the midst of a lunch meeting when I arrive, about 15 minutes too early. As I wait for her in the main lobby, the first thing that catches my eye is the photos. Hung on the walls are images of the cosmos – there’s one of the spiral galaxy NGC 7331 from NASA’s Chandra X-ray Observatory, which looks almost like blurry Christmas lights. Next to it is a picture of three black holes and a star swirling around one another, disrupting the surrounding cluster of stars. As starlight bends around the force of the black holes, it almost resembles obsidian marbles, suspended in a liminal space of goopy bubbles.
The moment Kalogera comes down the hall is brisk, almost like a whirlwind, though she stills with a warm greeting for me to catch up with her. She had been coming off of multiple other meetings that day – one with European collaborators in the morning to discuss software that would shape binary star modeling, another about diversity, equity, and inclusion at her research institute. Our interview is wedged right before her group meeting, where she will hear her students’ research as well as a guest from Johns Hopkins University.
“To get to the level where Vicky is and the things that she’s doing – not anybody can do that,” says Zoheyr Doctor, Board of Visitors Research Assistant Professor with Kalogera’s research group. “That really requires a tour de force of abilities.”
On top of her position as Northwestern faculty, Kalogera is the director and co-founder of CIERA. She tells me, “CIERA is a work of love.”
Kalogera started out her career at Northwestern as an assistant professor in 2001. Initially, she was most occupied with establishing her own research group from scratch. After she found her footing, she wanted to make something bigger.
“What I wanted was to work towards institutional change and enable other people to pursue top research, enable our students to have a top-level education in this area, because that’s my expertise,” she says.
Northwestern’s role in the world of astrophysics has had quite the growth spurt. Though it was not yet as prominent in the field when Kalogera first became faculty, she says Northwestern is now a top 10 program nationwide for astronomy and astrophysics.
“Professor Kalogera’s work as the co-founder and director of the Center for Interdisciplinary Exploration and Research in Astrophysics is second to none,” says Northwestern Provost Kathleen Hagerty over email. “She is one of the world’s leading astrophysicists and serves as a prime example of the remarkable drive of our faculty to discover new knowledge.”
CIERA is not a lab or observatory, as one might imagine. Instead of telescopes, there are winding halls of offices and conference rooms. “If you walk around, there’s students working at their desks and people working on whiteboards and people furiously trying to type Python code,” says Larson, who is associate director of CIERA. “It looks like normal university stuff.”
One might see a computer scientist working side by side with an astronomer at CIERA. “The product of the work, the collaborative things that we do, we try and do in a way that’s not possible when you don’t have as many experts around,” Larson says.
To work in this field is to never be alone. The spirit and connection of hammering away at a problem together keeps Kalogera in orbit with her work and her students. Her current group is a collection of undergraduates, graduate students, and postdoctoral fellows, alongside herself and Doctor. They’re gathered around a large conference room table when I follow Kalogera inside. With expertise ranging from data analytics to black hole binaries to star simulations, they’re enthralled with the idea of figuring out the nature of binary black holes and neutron stars.
“Even once we made those detections of black holes and neutron stars colliding, there’s another further question, which is how did that even come to be in the first place, that these two black holes were close enough that they could actually merge and we could see it,” Doctor says. “That is still a really big mystery in the field.”
The group meeting is two hours of questions and challenges lobbed back and forth (flying, also literally, over my head). When they pause for a break, Kalogera spends it meeting with individual students over a small shot of espresso, while others leave to grab drinks – sometimes in matching purple CIERA mugs, where the logo resembles a rising sun.
As the meeting resumes, one of her students gets up to present. Graphs resembling cityscapes blink by on the presentation, and the whiteboards eventually get filled with diagrams, formulas, and equations. Occasionally, a “Huh? I’m lost” comes up from Kalogera herself, though it’s all good-natured. She gets up to walk around, taking a marker to scribble her own math beside her student’s. She pokes and squeezes the theories, well in her element. But despite her challenges, it feels comfortable. The air hums with the electricity that comes with working with people who get you on the same wavelength.
It’s a spirit that has remained largely the same, even since the 2010s when Farr was a graduate student in Kalogera’s group. Back then, they focused more on developing parameter estimation – if a gravitational wave is like a bird chirping, Farr likens parameter estimation to identifying which bird was singing.
“It was kind of a no-holds-barred meeting where we would just get into the weeds on the problems we were dealing with,” Farr says. In a group where everyone is an expert in something, the questions always feed into answers into more questions. “The minute you get that feeling of, ‘Ah, now I understand this. That’s why.’ The minute you get to that answer, immediately, a new question pops into your head,” Kalogera says. “That’s what gets you going. That’s why we come in every day.”
***
In the beginning, Kalogera’s group was small. One of the first PhDs in her cohort was Chunglee Kim, recruited to Kalogera’s group in 2001. Their first impressions were over email, when Kalogera messaged Kim and introduced herself as a new faculty member at Northwestern. (Kalogera had also given Larson, then becoming a postdoc, an offer, though he ended up going to Caltech first – it’s an ongoing joke between the two of them, he tells me.)
Kim felt a sense of kinship and understanding with Kalogera, as they both were newcomers to the university and came from international backgrounds – Kim from Korea, and Kalogera from Greece. Their research group would gather in Northwestern’s Dearborn Observatory, right beneath the telescope. There, they read newly published scientific papers nearly everyday, while working on their own projects – in Kim’s case, a code that would eventually serve as a scientific motivator for the LIGO detectors.
In that room, there was no place for secrecy. Kalogera had big eyes for her students, Kim says. If their group was a family, then she was their big sister. She could solve problems, sometimes before Kim realized they arose. “She told me, over and over again, ‘Chunglee, you should have told me like a week ago! Don’t torture yourself!’” Kim says, laughing.
Almost 20 years later, Kim is now a professor in the physics department at Ewha Womans University in Seoul, Korea, as well as a member of the LIGO Scientific Collaboration. But she still remembers one question Kalogera had posed to her, back in her years as a graduate student, which she recounts to me now.
“‘Do you want to be a well-educated woman or do you want to be a scientist?’” Kim remembers.
Juggling what she describes as her more timid personality and the cultural shock from being in a new country, Kim says she understood the question to be a wakeup call, Kalogera’s way of pushing her out of her shell.
“I think that question is not radical, but very practical,” she says, “and led everybody to think. My personal reaction is that question is very useful and inspiring for female students in Korea.”
Astrophysics, like other sciences, has been a male-dominated field. But it’s essential that astronomers like Kalogera are familiar faces, opening paths for future astrophysicists looking to chase after the subject, according to Larson.
“That’s one of the important ways that we need to grow and change our field, so that people feel comfortable going into it, without thinking much about their identity,” he says.
Kalogera is also known among her colleagues, like Doctor, for laying the major groundwork for how astronomers can understand stellar binaries and their evolutions, specifically those including black holes and neutron stars. “So much of the work on that through the ‘90s, the 2000s, and beyond were papers she was on, or with people that she worked with, or people who came and were in her group here at Northwestern,” Doctor says. “She’s had a very outsized impact on this field.”
Sometimes, Kalogera would be the only woman in the room. But even in her high school years, when the challenges she faced targeted her identity first and ideas second, Kalogera says there was one thing that protected her.
“Having my teachers telling me, ‘You’re good, even though you’re a woman,’ did not faze me, did not…sort of hurt me deeply,” she says. “The reason was that I saw every little step, every opportunity I was getting already since high school, as a gift I was not gonna give up.”
Even as she advanced in her education, wading through the nagging questions of whether or not she belonged during her years as a postdoc and junior faculty, Kalogera never lost sight of her very first fascination – astronomy. “I’ll just enjoy every minute of it,” she says is the thought that kept her going. “And if it ends at some point, fine. But if it doesn’t, amazing.”
***
Now, LIGO, Virgo, and KAGRA are gearing up for their next observing run this May, after three previous ones. With each new run, their detectors become more and more sensitive. With those improvements, Kalogera says scientists could expect a higher rate of detections, possibly from a few to 10 black hole mergers per week. “Now we’re doing real astronomy,” she says.
With that growing body of observations, the collaboration will be able to fill existing knowledge gaps, such as the question of whether giant black holes over 80 times the mass of our sun, or smaller ones only about two and a half to five solar masses, exist. Kalogera says she is also looking for what she calls multi-messenger sources – the collision of two neutron stars. Unlike black holes, these dead stars contain matter, so when they collide, they form electromagnetic waves on top of gravitational waves. Having both messengers from these events can offer even more insight into their origins in the first place.
LIGO-Virgo has detected one such event in 2017, where for the first time, astronomers recorded the clash of a neutron star pair. Kalogera was heavily involved in the paper-writing and announcement of the discovery. But these multi-messenger observations are hard to come by. Both the elusive black holes and star crashes are rare objects in the universe. As detections pile up, astrophysicists can hope to sift through the sand of those observations, to discover such rarities.
To Kalogera, the growth of the gravitational wave field mirrors a century ago, when we were only aware of a singular galaxy, our own Milky Way. That lone fact bloomed into knowledge of our neighbors like Andromeda and the most distant galaxies at the edge of the universe.
“This is where we are with gravitational wave mergers,” she says. “Now we have about 100 mergers. With the next observing run, maybe we’ll go to 500 mergers. But we are where traditional astronomy of galaxies was a century ago.”
But when she thinks back to that first signal in September 2015, it’s still a moment to revel in. For Kalogera, the breakthrough came at the heel of years spent wading through the theoretical. Her work was all done on computers. The first detection of a gravitational wave provided irreplaceable physical evidence from an event we were never around to witness.
“Two black holes, over a billion years ago, collided into forming one black hole, and that signal was traveling all this time. And that Monday morning, that signal hit one of our detectors, and then seven milliseconds later, it hit the next detector. And we were there with our codes to detect it and measure the masses of the black holes.” To this day, she takes pause as she recounts this, a moment of breathing and knowing, we did that.
“I mean,” she says, “that was just life-changing.”
***
Somewhere in the universe, a giant star is burning out. After a brief existence – though one longer than any years a human or civilization could ever have – it’s burning through all the hydrogen in its core. The same way organs do at the end of one’s life, its reactions are slowing down. As the star’s core begins to collapse into itself, its outer layers will blow away, wisps of brilliant colors blossoming like an oil spill into space.
If the star is massive enough, it will eventually explode and collapse completely, losing to gravity. What takes its place is a seething emptiness astronomers call a black hole, which wields gravitational force so strong that, should it pass the point of no return, not even light can escape. Somehow, somewhere, it might fall into orbit with another black hole. They whirl round and round, spiraling closer to one another, until one day, their last moments as individuals blip in the form of a signal, recorded by a pair of L-shaped detectors on Earth.
And we could be none the wiser. We cannot feel gravitational waves, nor can we see them. Even the first image taken of a black hole was of its silhouette.
Why keep coming back to such distant things, after more than three decades? Kalogera’s reason is simple.
“You might think that what keeps me going back is that thrill of discovery, that one amazing day, right?” she says with a smile. “Although that was life-changing, it’s not really what gets you going, day by day. What gets me going and what keeps me going back is, really, more the thrill of our daily life.”
Most days at CIERA, it looks like fast-paced meetings. Once a week, Kalogera tries to have none at all, to preserve a day for thinking and reading (a highly difficult task, but one she undertakes nonetheless). Always, it’s the times that raise more questions than answers.
I ask Kalogera, near the end of our conversation, if there’s one thing in her career she hopes to figure out. She has been at the forefront of efforts to trace the moments of cosmic clashes. How those pairings came to dance in the first place is what Kalogera hopes to, one day, say for sure.
“Before I retire or drop dead – who knows,” she says, “if I can tell the story of, this is why pairs of black holes exist in nature and how they get to be the way they are, that will be cool.”
She adds, “I’m not sure we’re gonna make it, but that would be cool.”
And there are no existential crises here, she notes. Where do we come from? How did we get here? What does it even matter? Looking into the universe will inevitably stir up these age-old questions, but it’s the looking that helps.
“Of course, we don’t know everything,” Kalogera muses. “But getting a better and better understanding of what’s out there beyond the Earth, beyond our own solar system, beyond our own galaxy, lowers an anxiety, in a bizarre way.”
Think of the first time you saw the bigness of the world. Mine was seeing the real night sky, staring into an atmosphere unobscured by light pollution in the midst of a cooling desert. It was dark, but light shone everywhere. Everything feels miniscule when galactic dust and starlight populates every conceivable corner of the universe, always there even if left unseen. I remember that same wonder when I listen to Kalogera talk about her work and gesture toward the heavens. It’s an unforgettable feeling, like first love.
Why are we here? Kalogera doesn’t have a single answer that would satisfy everyone. But she’s found hers.
“Something about that work of studying the cosmos? It was really a fire in the belly. If you can feel that, for whatever one can do, follow it,” she says. “To me, that’s it.”
Katie Liu is a rising fourth year journalism major at Northwestern University, passionate about storytelling in science, culture, and arts.
