I am a NASA Hubble Fellow at the University of Chicago, working to understand how we can decipher the lives and deaths of stars using phenomena known as gravitational waves.
I received my PhD from Northwestern University in 2020, and my BS with majors in Astronomy and Physics from the University of Illinois Urbana-Champaign.
Predicted by Einstein over a century ago, gravitational waves are ripples in the fabric of spacetime.
Though any accelerating mass emanates gravitational waves, spacetime is very stiff and only extreme systems in the Universe can generate signals strong enough for us to sense.
I am a part of the LIGO Scientific Collaboration, which made the first observation of these elusive signals in 2015.
The culprit: two black holes about a billion lightyears away, each around 30 times more massive than our Sun, spiraling in towards one another and merging.
Since this groundbreaking discovery, we've observed dozens more gravitational-wave events, coming from both black holes and neutron stars.
These dark objects are the remains of massive stars when they die, and gravitational waves are providing a new means for observing and characterizing them in the Universe.
I aim to use the growing population of these observed compact objects to decipher information about their progenitors and better understand the impact that they have on the universe as a whole:
What type of environments were they born in?
What processes took place during the lives of their stellar progenitors?
What can we learn about the supernova explosions that create compact objects?
How do compact object mergers chemically enrich their environments with the heavy elements forged during their explosive merger?
What can compact object mergers tell us about star formation across over cosmic time?
Outside of astrophysics research I pass the time playing music: classical piano and string bass as well as bass guitar in a Chicago-based rock band (click here to listen to us on Spotify).
I love to travel and get lost in new corners of the globe, in winters particularly somewhere where I can snowboard.
Competitive tennis is my favorite form of exercise.
Having worked at a planetarium and in science education for multiple years, I'm also passionate about science education and outreach.
You can also find more about my outreach iniatives on this site.
Research
Throughout the history of astronomy, humanity has been reliant on one form of information to build our knowledge about the cosmos - light.
However, in the past few years, astronomers have unlocked a new messenger from the cosmos, a new sense with which to explore the universe.
This phenomena, known as gravitational waves, are minuscule ripples in the fabric of spacetime that encode information about objects with extreme gravity in the universe, such as black holes and neutron stars.
Where do Binary Black Holes Form?
Black holes and neutron stars are the remnants of massive stars.
Therefore, detecting these dark objects in gravitational waves offers a menas for understanding the lives of their progenitors, such as the environments they were born in, the complicated evolutionary processes that persisted throughout their lives, and the supernovae that marked their deaths.
To complicate matters, there are multiple pathways that astronomers believe may lead to merging compact objects, such as through the evolution of two massive stars in isolation or through dynamical encounters of black holes in dense stellar systems such as globular clusters.
These pathways predict different properties for the merging black holes, such as masses, spins, and orbital eccentricities, which are encrypted in the gravitational wave signals we detect.
I work to build statistical models which combine the growing observational sample of gravitational waves with detailed simulations of compact binary formation, providing insights into the relative efficiency of various formation channelsand constraining uncertain physical aspects of stellar evolution.
In dense stellar environments such as globular clusters, black holes sink into the cluster cores where stellar densities can be a million times higher than the stellar densities of our galactic neighborhood.
This leads to strong gravitational encounters between black holes, which can dynamically assemble new binaries that will merge through gravitational-wave emission.
Oftentimes, these dynamical dances can impart large eccentricities into the newly-formed black hole binaries, which can expedite their merger and will be a key distinguishing signature in the gravitational-wave data.
I am interested in modeling such encounters (see simulations here), and understanding how eccentric detections can determine the efficiency of dynnamical channels in synthesizing black hole binaries.
Ground-based gravitational wave detectors can also detect the merger of the dense remnant cores of massive stars, known as neutron stars.
The first detection of merging neutron stars in August 2017 and was accompanied by a rainbow of light across the entire electromagnetic spectrum from the subsequent kilonova explosion and gamma-ray burst.
This discovery was the first to combine gravitational waves and light to build a better understanding of an astrophysical event - the "holy grail" of multi-messenger astronomy.
I also study how we can use such detections, as well as detections of other high-energy transients such as short gamma-ray bursts, to extrapolate backwards in time and learn about the stellar system that formed the neutron stars and the evolution of their galactic hosts.
The supernovae that form neutron stars also lead to a great migration, oftentimes flinging the system to the outskirts of its galactic host.
The location of the merger relative to the host galaxy can therefore illuminate uncertain aspects of supernova physics.
When neutron stars merge, they enrich the cosmos with some of the heaviest elements in the Universe, such as gold and platinum.
Looking at the abundance of these "r-process" elements in different galactic environments can therefore tell us where and when neutron stars were merging.
I study how observations of r-process enriched stars in galactic environments such as such as globular clusters and ultra-faint dwarf galaxies can help decipher aspects of massive binary star evolution and neutron star formation.
Many aspects of massive-star evolution are highly uncertain, and this uncertainty becomes even worse when dealing with stars that are in binary systems (which most massive stars are).
To constrain these physical uncertainties, we can turn to population synthesis, where we can rapidly simulate large populations of systems such as binary black holes and binary neutron stars using various physical assumptions.
These populations can then be compared with the observation sample of systems detected with gravitational waves or other means.
I have worked to help develop a population synthesis code called COSMIC, which is completely open source and version controlled.
I've used this code to investigate some of the most exceptional gravitational-wave events to date, such as the merger of a black hole with a compact object that lies in the regime between known black holes and neutron stars.
The properties of compact binaries detected via gravitational waves, such as their masses, spins, and redshifts, are determined through Bayesian parameter estimation.
In some cases, the inferred values of such parameters can change when different Bayesian priors are assumed, which account for one's prior belief in a particular problem.
I'm interested in investigating the robustness of parameter estimates to differing prior assumptions, particularly astrophysically-motivated and population-based priors.
For example, by performing analyses with different prior assumptions, we found that the first measurement of non-zero component spin in a binary black hole merger can robustly be attributed to the larger of the two black holes in the merger.
One other area of research I am involved in is "citizen science" - involving the general public scientific data analysis through crowdsouring.
I helped to build the first gravitational-wave project on the Zooniverse citizen science platform: Gravity Spy.
Being the most sensitive gravtitaional experiment ever built, the LIGO detectors are susceptible to sources of environmental and instrumental noise, known as "glitches", which afflict our sensitivity to the gravitational-wave universe and can even masquerade as astrophysical signals.
A comprehensive characterization of such noise signals is paramount to the LIGO and Virgo detectors achieving their sensitivity goals.
However, as hundreds of thousands of glitches occur in the detectors during an observing run, this task would overwhelm any small group of scientists.
The Gravity Spy project combines the power of machine learning algorithms withs volunteers from the general public to look at gravitational-wave data containing glitches, and better understand where such sources of noise come from.
This project has been highly successful, with over 3.8 million classifications from over 22,500 registered users to date.
Creating a symbiotic relationship between volunteer classifications and machine learning will help to scale citizen science with the ever-increasing datasets of the future.
COSMIC: Open-Source Binary Population Synthesis.
K. Breivik, S. Coughlin, M. Zevin, C. Rodriguez, K. Kremer, C. Ye, J. J. Andrews, M. Kurkowski, M. Digman, S. L. Larson, F. A. Rasio.
The Astrophysical Journal 898, 71 (2019).
Black Holes: The Next Generation.
C. Rodriguez, M. Zevin, P. Amaro-Seoane, S. Chatterjee, K. Kremer, F. A. Rasio, C. S. Ye.
Physical Review D 100, 043027 (2019).
On the Progenitor of Binary Neutron Star Merger GW170817.
The LIGO Scientific Collaboration and Virgo Collaboration (M. Zevin: Chair of paper-writing team and analysis lead).
The Astrophysical Journal Letters 850, L40 (2017).
The following simulations show gravitational-wave captures that results from the encounter of four black holes, which can occur at the cores of dense stellar systems such as gloublar clusters.
Such encounters can lead to long-lived "resonating" interactions, through which many temporary binary systems are created.
When one correctly includes post-Newtonian terms in the equations of motion, the formation of a highly eccentric binary can lead to a rapid inspiral and merge due to gravitational wave emission zapping orbital energy.
These mergers can maintain their high eccentricies into the LIGO sensitive frequency range and occur at a rate accessible by advanced LIGO.
If detected, such systems will highly constrain their formation scenario and be a clear indicator that dynamics can play a key role in facilitating binary black hole mergers.
Examples below are from Zevin et al. 2019 (ApJ 871, 1).
The Final Flight of a Binary Neutron Star
The following animation shows the kinematic evolution of a simulated double neutron star system that may have been the progenitor of GW170817.
Using the observed offset of GW170817 from its host galaxy (NGC 4993), we can constrain aspects of the stellar evolutionary process that led to its formation.
The pair of stars—a neutron star and a normal star—orbit quietly, until the normal star undergoes a supernova, spawning a second neutron star and “kicking” the system into an elliptical orbit.
The two neutron stars eventually merge and generate gravitational waves, a gamma-ray burst, and an explosion called a kilonova. Other potential lives are shown in the thinner, lighter-colored lines.
Data for this animation comes from the analysis in Abbott et al. 2017 (ApJ 850L, 40A).
Outreach
Astrobites
Astrobites is a daily astrophysical literature journal written and run by graduate students in astronomy.
Since its inception in 2010, Astrobites has published over 2000 and the site reveives about half a million visits a year.
I spent two years as a regular author on Astrobites (you can read my posts here) and now serve on the leadership team for Astrobites.
One of the things I was most proud of helping to develop were the Beyond astro-ph series of posts, which are written instead of the standard astro-ph summary once every couple weeks and cover topics ranging from career advice to classic astrophysical papers to the state of diversity and inclusivity in astronomy.
Astrobites is now partnered with the American Astronomical Society.
Astronomy on Tap
Astronomy on Tap is a worldwide series of informal presentations on astronomy, hosted at local bars and breweries.
Along with several other graduate students and postdocs at Northwestern, I helped start the local Chicago chapter (Facebook, Twitter).
We've been lucky enough to partner with some great breweries all around the Windy City, such as Begyle Brewing Company, Empirical Brewery, Half Acre Beer Company, Metropolitan Brewery, and Smylie Bros Brewing so far.
We also are partnered with the Adler Planetarium, and host live astronomy trivia at their monthly 21+ Adler After Dark event.
Astronomer Conversations at the Adler Planetarium
Once a month, I present at the Adler Planetarium's Space Visualization Laboratory (SVL).
The SVL provides a platform for the general public to ask experts about the latest space news and hear about the cutting edge astrophysical research taking place in Chicago.
The beautiful visualizations which accompany the talks make if truly an immersive experience, both for the audience and the speaker.
ComSciCon
ComSciCon is a series of workshops focused on the communication of complex and technical concepts organized by graduate students, for graduate students.
ComSciCon attendees meet and interact with professional communicators, build lasting networks with graduate students in all fields of science and engineering from around the country, and write and publish original works.
After attending the national ComSciCon workshop in 2017, I become a part of the Program Organizing Commitee for the national workshops.
Astronomer organizers/attendees from the 2019 national workshop are shown above.
I had to leave early to catch a flight, so I appreciate the excellent photoshop skills used to stitch me in!
Gravity Spy
Gravity Spy is a citizen science project hosted by Zooniverse that characterizes troublesome noise in the LIGO and Virgo gravitational-wave detectors.
During my PhD, I helped to build this project, and have been the point-person on the team for interacting with our volunteer base.
Since its inception in October 2016, the project has accumulated over 3.8 million classifications from over 22,000 registerd volunteers.
Besides the contributions that this project has had in LIGO detector characterization efforts (see my Research page), Gravity Spy has allowed tens of thousands of volunteers from all over the world to be immersed in cutting-edge scientific research.
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