The year 2015 marks the centenary of Einstein’s general relativity, the remarkable theory he came up with in 1915 to merge relativity and gravity. Over the last 100 years, general relativity has been tested with many experiments, and it has passed every test convincingly. Nevertheless, one area remains unproven: black holes, those mysterious objects that have event horizons -- surfaces through which things can fall in, but from inside which nothing, not even light, can escape. Black holes are a direct prediction of Einstein's theory of general relativity, but they are so strange and bizarre that Einstein himself doubted their existence. Yet, astronomers have found countless objects in the universe that they believe to be black holes. But believing is not the same as proving, and it is very difficult -- nearly impossible -- to prove that a candidate object is truly a black hole. Dr. Ramesh Narayan, Thomas Dudley Cabot Professor of the Natural Sciences at Harvard University, uses astrophysical and computational techniques to study this and other fundamental questions surrounding the paradox of black holes. Just as any basic science research can potentially find practical applications down the road, the understanding that Dr. Narayan brings to black hole astrophysics may be foundational to how we perceive the world in the future.

Dr. Narayan is a theoretical astrophysicist who has worked in many areas of research within astronomy, astrophysics, and cosmology. He has worked on topics as diverse as astronomical image processing, gamma-ray bursts, gravitational lensing, pulsars, quasars, and X-ray binaries. For the last two decades, however, he has focused almost exclusively on black holes, with much of his work done in collaboration with Dr. Jeffrey E. McClintock, a Senior Astrophysicist at the Smithsonian Astrophysical Observatory. As a leader in the astronomical community, Dr. Narayan regularly produces high-quality astrophysical results on black holes. He is also highly respected in the physics community, especially by scientists working in gravitational physics and general relativity.

Dr. Narayan’s research on black holes follows two tracks:

• Developing Models: Dr. Narayan seeks to develop models to explain the wealth of observational data that is available on astronomical black holes. In particular, he studies the process of gas accretion on black holes which causes huge amounts of radiation to be emitted by the accreting gas. This radiation is seen in many bands: radio, infrared, optical, ultraviolet, X-rays, and gamma-rays. Dr. Narayan models the accretion process using both theoretical methods and numerical computations with high performance national supercomputers, and he attempts to understand how the observed radiation is produced.
• Understanding Black Holes: Dr. Narayan seeks to use his theories, coupled with observations, to answer some of the deepest questions on black holes.
  • Are the objects that scientists study in astronomy really black holes? In order for an object to qualify as a black hole, it must possess something called an “Event Horizon,” a surface of no return, from which not even a light ray can emerge. But proving that an object has an event horizon is extremely difficult since the horizon produces no signals. Dr. Narayan looks for evidence of event horizons by taking various indirect approaches.
  • Even though no signals can come out of a black hole, is it still possible for energy to flow out? In 1969, Dr. Roger Penrose at Oxford University argued that a spinning black hole is a potential source of energy which is available to the outside world. Various astrophysicists have since proposed mechanisms whereby this energy might produce observed phenomena like “Relativistic Jets.” Dr. Narayan studies the viability of these ideas using computer simulations. He also searches observational data for direct evidence of energy extraction from spinning black holes.
  • Is it true that black holes are the simplest objects in classical physics? According to general relativity, each black hole is completely described with just a few numbers: mass, spin, and, possibly, electric charge. Dr. Narayan looks for tests of this remarkable theoretical prediction.

Dr. Narayan’s work in the first track above, “Developing Models,” lies within mainstream astrophysics and is viewed favorably by astronomy funding agencies. However, his work in the second track, “Understanding Black Holes,” is viewed by these same agencies as physics research and therefore not appropriate for their support. Meanwhile, physics funding agencies think the work is astronomy-related and not suitable for physics funding either! Private funding is therefore invaluable to continue this kind of interdisciplinary black hole research, which is central to our understanding of gravity and the universe.