Priyamvada Natarajan Explores the Secrets of the Universe

June 25, 2024

Fewer than 500 million years after the birth of the universe, an unusually large black hole called UHZ1 began to vomit immense quantities of electromagnetic radiation into the cosmos. The flares of light it emitted can still be detected today. As they appear on humanity’s most advanced telescopes and observatories, they’re helping Priyamvada Natarajan, Joseph S. and Sophia S. Fruton Professor of Astronomy and Professor of Physics and Chair of Astronomy at Yale, explain the history of the universe. Natarajan’s work is so monumental that she was named one of Time magazine’s “100 Most Influential” people of 2024. 

Natarajan has long been fascinated by black holes. Writing by email, she told me, “In general I have always been enthralled with the invisible universe—the entities that lurk behind the twinkling stars that we can see. These invisible ingredients are all pretty elusive; we cannot image or detect them directly. We only infer their presence indirectly. This is such an inviting puzzle that I was drawn in once I saw the night sky through a telescope when I was a young girl growing up in Delhi. Black holes are some of the most enigmatic objects in the cosmos. They represent the limits of our knowledge and we are really pushing at the limits of understanding of physics when we study them.” 

Some of her most prominent work has focused on a class of black holes that were, until now, a mystery: supermassive black holes from the early universe. For most of the last century, scientists have thought that supermassive black holes form through one of two routes: as the products of collapsing giant stars after a supernova; or through collisions between multiple black holes. Beginning in 2006 and 2007, Natarajan proposed a new route for supermassive black hole formation that would result in “heavy” black hole seeds as opposed to the “light” black hole seeds of collapsing stars. 

In Natarajan’s theory, which she further refined in a 2017 paper, she hypothesized that supermassive black holes in the early universe might have formed out of collapsing galactic gas clouds, skipping the intermediate stellar stage and going straight from gas cloud to black hole. If it could be empirically supported, Natarajan’s hypothesis would account for supermassive black holes that predated the collapse of any stars large enough to form them. In the same 2017 paper, she noted that the in-development James Webb Space Telescope, which was launched in 2021, would have the ability to detect the signals of these kinds of supermassive black holes.

“When I first wrote the paper suggesting direct collapse of gas as a way to form heavy black hole seeds,” Natarajan told Yale’s Jenny Blair earlier this year, “colleagues said, ‘This is just too speculative. Sure, the physics works, but it can’t be real.’” In a 2023 paper, Natarajan, working with astrophysicists from Princeton University and Harvard University’s Black Hole Initiative, showed that it was very real. Using light and x-ray observations of UHZ1, Natarajan and her colleagues found that UHZ1’s “characteristics are in excellent agreement with prior theoretical predictions for a unique class of transient, high-redshift objects, Over-massive Black Hole Galaxies [OBGs] by Natarajan et al. that harbor a heavy initial black hole seed that likely formed from the direct collapse of the gas.” That finding helps validate Natarajan’s hypothesis and shows that there is much more work to be done to understand the history and variety of black holes in the early universe.

Natarajan’s groundbreaking work on heavy black hole seeds, as well as her research on black hole growth, the first stars, and gravitational lensing, has earned her accolades from her fellow researchers, not just Time. In February, she was one of 21 scientists elected to the American Astronomical Society for her “seminal contributions to our understanding of the nature of dark matter and black hole physics, and for the development of a brand-new framework that enables mapping the detailed distribution of dark matter on small scales within galaxy clusters using gravitational lensing.” She is an elected fellow of the American Academy of Arts and Sciences, the American Physical Society, and the American Association for the Advancement of Science, as well as the recipient of Guggenheim and Radcliffe fellowships. Her time at Yale has been marked not just by her astrophysics research, but also by a commitment to mentoring women in the sciences and to engagement between science and the humanities, as well as to the South Asian Studies Council. She said, “The feeling of belonging is critical for me to thrive intellectually—and SASC is a wonderful and diverse community that has greatly contributed to that sense of being accepted, respected and celebrated. It has been a joy to be involved and be a member and serve on the Executive Committee.”

As she looks forward to new research projects, including further work on black hole formation in the earliest seconds of the universe as well as a book for the broader public on the scientific ideas and progress. She will be doing so with greater public attention—and enthusiasm—for her work than ever before, which she told me she welcomes. “It’s awesome to see the growing public interest in our work as astrophysicists—it’s great to share the excitement of what we have the privilege of getting to do as our jobs. Humans have always been in awe of the cosmos, it’s in our DNA, so it’s unsurprising at some level to see the public so engaged. I hope this collective sense of awe brings us all together transcending all the conflict and chaos in the world.”

Byline: Daevan Mangalmurti