Five Questions With: Gaurav Khanna

Gaurav Khanna, an associate professor and associate director of the Center for Scientific Computing & Visualization Research at the University of Massachusetts Dartmouth, talked with Providence Business News about his research into black holes. Khanna worked with researchers at Georgia Gwinnett College and the University of Maryland to develop the first-ever computer simulation of the interior of a rotating black hole. Their research was supported by the National Science Foundation.

PBN: How long have you studied black holes?

KHANNA: For some context, let me briefly comment on some history here. Einstein developed his theory of gravity, so-called general relativity over 100 years ago in 1915. It was Karl Schwarzschild who used this theory to (mathematically) derive the notion of a black hole, while serving as a soldier on the front in World War I. So, interestingly the early work on these concepts is a century old!

I’ve been fascinated by Einstein’s theories since I was in high school .. nearly 30 years ago now. But, I formally began studying gravity and black holes when I went to graduate school at Penn State in 1995. And a day hasn’t gone by since that I stopped working toward a better understanding of these fascinating astrophysical objects in our universe. Therefore, I’ve been in this field for over 20 years.
PBN: How long did it take you and your team to develop the computer simulation of the black hole’s interior?

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KHANNA: My close collaborator (Dr. Lior Burko) and I first spoke the possibility of simulating the interior of a rotating black hole almost 15 years ago in 2002. We did make a few attempts at that time, but were largely unsuccessful. Our mathematics and computational technique was not advanced enough at that time to perform a meaningful simulation. We hesitantly gave up on it for many years … but then started discussing it again two years ago, because we realized that techniques that we had developed for an unrelated problem could potentially be applied to the interior simulation as well.
PBN: What happens inside a black hole?

KHANNA: The inside of a black hole houses perhaps the most bizarre things in nature. These are called “singularities” and are regions wherein the mathematics appears to simply break down. Physically, singularities are places where common quantities like temperature, pressure, density etc. literally become infinitely large – a bit like at the moment of the “big bang” when our universe was created. The expectation has always been that these singularities would forbid anything from surviving a journey into a black hole, simply because it would be instantly incinerated.

What we were able to show using our computational research is that in the context of a rotating black hole, there is a sort-of loop hole. The problematic singularity is actually a “weak” singularity … essentially it is like a really thin pancake … and a falling object may not be harmed by it.
PBN: Can you explain how supercomputing was used in this project?

KHANNA: Supercomputing played a crucial role in our work for two reasons. First, all the “action” happens in a small region inside the black hole, so we had to make sure that that region was being represented and resolved extremely well in our computations. We performed many, many tests to make sure that our results were robust. Second, because of the singularity, there are physical quantities in our simulation that grow very fast (some growing as much as 300 orders-of-magnitude!) and that requires very high-precision, highly intensive computations.

We used very high-end graphics-processing-unit (GPU) based, compute servers to perform these sophisticated computations. These servers are available as part of the research facilities of the Center for Scientific Computing & Visualization Research at UMass Dartmouth.

PBN: How do you think the research will be used?

KHANNA: Any research that contributes to the fundamental understanding of the most mysterious objects in our universe, advances science in significant ways. Our work may lead to a better understanding of gravity, which happens to be the oldest known, but least understood force of nature. On a more “practical” note … our work suggests that black holes may actually be usable as portals for hyperspace travel in the distant future!

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