When Yale astrophysicist Priyamvada Natarajan is not chasing black holes, sifting dark matter or lassoing receding galaxies, she can pause just long enough to give you a guided tour of the universe



By Rakesh Krishnan Simha


Priyamvada Natarajan has gone over to the dark side. Quite literally. When the Yale astrophysicist peers into the night sky she doesn’t normally look at the stars, but instead scans the vast blackness of space between those shimmering stellar bodies. For, in that inky void hides dark matter, the most elusive substance in the universe.

Finding dark matter could well be the holy grail of cosmology. According to Natarajan, who is professor, Departments of Astronomy and Physics at Yale University, it accounts for over 96 percent of the mass of the known universe. The ordinary matter that makes up everything we can see, including the stars and planets, comprises just 4 percent of the cosmos. In fact, some astrophysicists claim that dark matter outweighs regular matter 30 to 1 in most galaxies in the universe.

Dark matter matters because the entire jing-bang of the universe rests on it. Okay, unlike climate change or greenhouse gases it won’t affect our chances of survival but on a cosmic time scale, it has huge implications. The universe, as we know, is expanding and galaxies are flying away from each other at astonishing speeds. If this expansion doesn’t stop, then after billions of years, humans (assuming we are still around) will see fewer and fewer stars because these astral bodies will slowly drift away from us, until there is nothing but complete darkness in the night sky. All the galaxies would have receded forever from each other. ­Ultimately, when the fires in all the stars die out, the universe would be a burnt out cinders.

This image shows the inner region of Abell 1689, an immense cluster of galaxies located 2.2 billion light years away. Dark matter in the cluster is mapped by plotting the plethora of arcs produced by the light from background galaxies that is warped by the foreground cluster’s gravitational field. Dark matter cannot be photographed, but its distribution is shown in the blue overlay. The dark matter concentration and distribution is then used to better understand the nature of dark energy, a pressure that is accelerating the expansion of the universe.

Credit: NASA, ESA, E. Jullo (JPL/LAM), P. Natarajan (Yale) and J-P. Kneib (LAM)

The outward accelerating expansion is counteracted by the force of gravity. If dark matter dominated it would cause the universe to ultimately grind to a halt and begin to collapse under its own weight, imploding in a catastrophic finale, after which there would be another Big Bang, leading to the rebirth of the universe. 

But wait, things now get trickier. The discovery of dark energy in 1998 suggests that an even more mysterious force is powering the accelerating expansion of the Universe. 

Well, in either event we’ll all end up dead, but at least dark matter gives us another chance.

PROUD MOMENT: Priyamvada Natarajan is the 2009 recipient of GOPIO Connecticut’s Award for Academic Achievement

Sounds exciting, doesn’t it? Clearly, Natarajan works in rarefied fields where ordinary physicists fear to tread. “I work on exotica in the universe,” she says. Indeed, when she’s not hunting dark matter, she’s into black hole physics and gravitational lensing. Now that’s exotic.

Natarajan sheds some light on dark matter: “We know it has mass, it clusters and aggregates spatially and is probably a particle that was created in the very early universe right after the Big Bang. Since it has mass it exerts a gravitational force in its vicinity and that is how we infer its presence. My work has revolved around mapping the distribution of dark matter using gravitational lensing which is the phenomenon of the bending of light as light travels through large distances in the universe.”

As for the subject of black holes, they are objects of such incredible gravitational pull that they suck in everything—including light, stars and entire galaxies—that come within their grasp. It was another brilliant Indian scientist S. Chandrasekhar who gave us the Chandrasekhar Limit, or the size of a star that would turn into a black hole. Natarajan takes it further—she works on understanding how black holes grow and evolve, and has shown in her work that these galactic vacuum cleaners also end up stunting their own growth, i.e. there is an upper limit to black hole masses. Astronomical observations have shown recently that every galaxy in the universe—eerily, including our own Milky Way—harbours a black hole at its centre. “So the process of formation of a galaxy is intricately linked to the formation of the central black holes,” she says.

Natarajan also punctures a popular myth. If you have pictured black holes as unstable objects, then be prepared to be disappointed. “Real astrophysical black holes, as opposed to black holes in movies and books, appear to be pretty stable, yet fiery and tumultuous, entities,” she says.

While it’s fascinating to soak up all this spellbinding information that Natarajan churns up, what’s remarkable is that her particular field of theoretical cosmology has very few women, less than a handful. So how did she manage to kick in the doors at America’s elite male-dominated institutions?
Natarajan starts at the beginning. “I grew up in Delhi, and was always interested in science as a child,” she says. “Both physics and mathematics fascinated me. I come from a family where the life of the mind, being an intellectual, is the norm, so I had plenty of books, encouragement and support around me always.”

“Also I had some excellent physics and mathematics teachers in school. I got my first taste for research while doing research on sunspot activity under the direction of the late Dr Nirupama Raghavan —the then director of the Nehru Planetarium in Delhi—when I was in high school. I really enjoyed the process of discovery and of pushing myself to understand complicated phenomena and was hooked.”

Hard work and brilliance formed a potent mix. Natarajan won a rare scholarship to study at the Massachusetts Institute of Technology as an undergraduate. Along with her studies in physics and mathematics, the young undergraduate was actively pursuing research on an interesting problem pertaining to the early universe. She subsequently went to Cambridge University with an Isaac Newton Fellowship at Trinity College to pursue her PhD in theoretical astrophysics.

Today, Natarajan plays a stellar role in astrophysics. Currently, she is on leave from Yale to take up her Guggenheim Fellowship this academic year (2010 - 2011). She was a JILA Fellow at the University of Colorado at Boulder in September and October, 2010. Since November 2010 she is a visiting professor at the Institute for Theory and Computation at the Harvard Smithsonian Center for Astrophysics in Cambridge. She will also be enrolled as a graduate student in the Spring of 2011 at the Program in Science, Technology and Society at MIT.

Natarajan is the Caroline Herschel Distinguished visiting fellow at the Space Telescope Science Institute in Baltimore this year and holds the Sophie and Tycho Brahe visiting professorship at the Niels Bohr Institute in Copenhagen. She will be wrapping up the academic year in May-June 2011 with a fellowship at the Rockefeller Bellagio Center in Italy.

Natarajan was also a 2008 recipient of a Radcliffe Fellowship; a 2009 recipient of the India Abroad Foundation's "Face of the Future" Award. She was the 2009 recipient of the award for academic achievement from the Global Organization for the People of Indian Origin (GOPIO). She is a fellow of the Royal Astronomical Society and was recently elected a fellow of the American Physical Society.
Natarajan is impressed with the progress of astrophysics in India. According to her, there is a very active theoretical astrophysics and cosmology community is India and a lot of young people are returning to work here in research careers so the prospects are great.

“We need to encourage kids and younger people to think about careers in research in science. These are very satisfying and fun professions and we need young people to come into this field,” says Natarajan, who is now planning to help organise a Science Festival in Delhi in 2011.

Once upon a time space was the final frontier. However, cosmologists like Natarajan have pushed that frontier further and further out to the deepest beyond, where only the most dogged minds are able to peer into. Modern cosmology is extremely challenging, fast moving and highly competitive, and we are at a stage where observational data is copious so theoretical work necessarily needs to be able to explain what is seen. People like Natarajan work on the late universe for which there is now a lot of data, where others like Stephen Hawking work on the very early universe for which there is no real data available so there is a lot more room for speculation.

So what’s set for the future? Natarajan is now keeping her fingers crossed for the OMEGA Project, which will map the granularity and detailed spatial distribution of dark matter which will hopefully yield clear clues to its very nature. Unlike Pentagon generals and Olympic athletes, astrophysicists have to live with the reality of budget constraints, so it could be a decade before OMEGA gets the green light. “It’s at the proposal stage, but I’m optimistic,” she says.

Writers hate using clichés, but this is as good an occasion as any to say, “Watch this space.”

January 2011

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