In this series of posts, we sit down with a few of the keynote speakers of the 243rd AAS meeting to learn more about them and their research. You can see a full schedule of their talks here, and read our other interviews here!”
A New Era for Astronomy
“It’s very exciting for us because it’s the culmination of 15 years of hard work, and really gets us on the road to even more discoveries,” Stephen Taylor, assistant professor at Vanderbilt University, and chair of the NANOGrav Collaboration, says as he explains the science behind NANOGrav’s evidence for a nanohertz gravitational wave background. The announcement in June 2023 from the members of the International Pulsar Timing Array, which includes NANOGrav, presented many years of analysis of correlations between pulsars influenced by an all-sky background of gravitational waves (GWs). For this transformative achievement Taylor is being invited to give the Fred Kavli Plenary Lecture at AAS 243. Unlike GWs detected by ground-based detectors such as LIGO, Virgo and KAGRA, for nanohertz GWs “the other side of the optical bench is the pulsars themselves”, which are precisely characterised down to the millisecond, and the GWs are “at a wavelength on scales of a light year” he explains.
Taylor is a first-generation university student – both his parents left school at age 16. “Even though they might not have quite understood what’s involved in academic research or why it was important, they were adamant that I pursue something I’m passionate about,” he says of his experience growing up. Going through academia was a process of trial-and-error, as he lacked some of the generational knowledge transfer useful for academic progression, from knowing how to do a university interview to getting research opportunities to go to graduate school. What helped Taylor the most was the great mentors he met along the way – something he stresses is important for any student, and when he can he likes to mentor other first-generation students to try to pass along some of the lessons that he’s learned today.
His academic path has spanned multiple continents, and despite claiming to be very bad at networking, he found new opportunities as “people were generous with their time”. “I got to work with really talented wonderful people at JPL and Caltech,” he says, which was a strong motivating factor in his career. “It’s inspiring to be in a place where you feel like people are much smarter than you are, it caused me to up my game quite a lot”.
“[At NANOGrav] you come for the science but stay for the people.”
Despite only pivoting to pulsar timing arrays (PTAs) in his PhD due to his original research plans taking an unexpected turn, it worked out for the best as he stuck with it ever since. After more than a decade of work, now having the evidence of a nanohertz GW background he says “immediately allows us to do tons of other science like recording the census of a population [of supermassive black hole binaries (SMBHB)]”. One of the predicted types of sources for this GW background is pairs of the most gigantic black holes in the universe, which originate from the very centre of galaxies and release nanohertz GWs while merging after galaxies collide together.
When I ask him what he is most looking forward to now that a new window into GW astrophysics has been opened, he expresses his eagerness for finding an individual SMBHB amongst the background. “What really excites me is the prospects for multi-messenger signals,” he explains, “if [the signal] is truly being produced by a SMBHB background, we should be able to bring the loudest binaries into focus”. The binaries making up the signal could be merging in gaseous disks from the aftermath of the galactic collisions, meaning we could observe them not only with GWs but also with electromagnetic light, two different universal messengers. Seeing these accretion disks being torn apart or powerfully beamed could lead to variability in their electromagnetic brightness, something we can learn more about with instruments like the Vera Rubin Observatory. “By fusing this information together you’re getting a more complete portrait of [these systems],” Taylor says about connecting nanohertz GWs with EM observations, “they trace out the binary dynamics in complementary ways”. Altogether nanohertz GWs “tie together a lot of different subfields in astrophysics”, from disks in strong gravitational fields to SMBH growth and evolution across cosmic time.
To dig deeper into the mammoth task of the new astrophysics this detection unlocks, Taylor’s research group at Vanderbilt is focusing an a wide array of data analysis problems, from rapidly fitting models of the GW background in minutes (previously done in days-weeks), to localising potential host galaxies for individual SMBHB sources, and confronting new challenges with deep learning and AI.
Of NANOGrav, Taylor exclaims “here you come for the science but stay for the people”. He explains that NANOGrav is still of the size that you can know most of the people, and it is tight-knit and inclusive. He adds that finding people you can work well with makes a big difference to your life as a young academic: “Getting a good match with a PhD advisor is something very important. Really asking lots of questions, and doing some trial projects if you can and seeing what really fascinates you”. In addition to this, getting research experience even if it’s just a summer or a semester with an advisor that’s local to you allows you to “see what you enjoy doing, see what you enjoy learning and importantly see what you don’t enjoy doing”, he advises.
Together We Can Build a Diverse Future
Taylor is additionally setting the standard for fostering diverse, inclusive, and equitable science with the EMIT training program at Vanderbilt, saying “It’s a once in a generational chance to seed a new field with these principles so we’re hoping to do it right.” His last comments touch on the exciting future of astrophysics over the next few decades: “It’s an exciting time to be a student in astrophysics. We have this entirely new messenger that we can use to probe some of the deepest mysteries of the universe. Entwined with that you have these emerging new technologies. There’s plenty of opportunity to make a big impact.”
To hear more about the exciting future of nanohertz gravitational wave astrophysics, tune into Stephen Taylor’s Plenary Lecture at 8:20 AM CT on Monday, January 8th at #AAS243!
Edited by: Megan Masterson
Featured Image Credit: AAS
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