UI team played major role in black-hole breakthrough

UI team played major role in black-hole breakthrough

The worldwide Event Horizon Telescope Project has captured the first-ever image of a black hole, at the center of a giant galaxy in the constellation Virgo, 55 million miles away.

University of Illinois physics and astronomy Professor CHARLES GAMMIE led the theory working group for the scientific collaboration. His team, which included UI graduate students BEN PRATHER and CHARLES WONG, helped interpret the data that produced the historic image.

It also enabled scientists to determine the mass of the massive black hole (6 billion of our suns) and shed new light on its mysterious "plasma jets."

Staff writer Julie Wurth spoke to Gammie, who was in Washington, D.C., for Wednesday's announcement:

What was it like to see the actual image after all of your theoretical work?

It was fabulous — very gratifying, and actually a little surprising that it looks so much like what we all had predicted.

It's something that we have been working on at Illinois for more than 15 years, aspects of this, and really intensively over the last year. My students haven't slept in six months, and neither have I.

How long did your part of the project take?

The data was gathered in April 2017. It was then shipped back to two centers, one at MIT Haystack Observatory and one in Bonn, Germany, for first analysis. What we did at the end was help interpret the data. We built theoretical models of what you see in the image that involves big supercomputing simulations.

U of I has long been a leader in this business. NCSA was founded by a guy who was working on a very similar problem, Larry Smarr. He had a graduate student who was my postdoctoral adviser many years later. They went to Germany to work on his student's thesis and found a supercomputer they could work on. They realized it was really great and they needed one.

Why is this milestone so significant?

It does cast Einstein's theory of gravity in a new regime, but it's also interesting for understanding how black holes work out in nature, sort of far away from the theorist's chalkboard.

There they sit in these messy environments which are the centers of galaxies, where there are all kinds of weird stars and gases around. Oftentimes, they produce powerful jets of gas that emerge from the centers of galaxies.

That's what we see in Messier 87, the system that we studied. That thing has two jets of gas that come out of the middle of the galaxy. It's long been a mystery what powers those jets. I think that our theoretical analysis strongly suggests that the jets are powered by the black hole itself, by the rotation of the black hole.

The magnetic fields near the black hole brake or slow the rotation of the black hole, transferring its rotational energy to the surrounding hot gas, which in turn forms the jets.

No light can escape from black holes, so what is the glowing ring around the black hole in the image?

It's the event horizon, the point of no return. The glowing stuff comes from gas falling into the black hole. The stuff that's falling in gets really, really hot, to temperatures of a billion or more degrees. So it glows.

Is what we see the actual size?

The gravity of the black hole bends the light around the black hole. So when this gas that's falling in produces light, that light gets bent. The net effect of that is to really emphasize the brightness of the ring around the hole. It makes the ring brighter.

The black hole looks bigger in the sky because of "gravitational lensing." It's about five times bigger than the actual size. The black hole is still bigger than our entire solar system.

You've said scientists hope to add radio telescopes to the Event Horizon network and eventually put some in space, to get higher-quality images. How would that work and how far away is that?

By using telescopes all over the Earth, you're getting as fine a resolution as if you had a telescope the size of the Earth. If you make it bigger, you get even finer resolution. So if you put something in space, you get finer resolution.

I thought it was about 10 years away, but I talked to an engineer who's working on it today, and she told me it was only five years away, which would be amazing, if true.

But any space mission is expensive. It would mean at least hundreds of millions of dollars. There are at least two proposals that I know of, one from Europe and one from the United States. The way these things usually work, at the end there's some collaboration and there's one mission that flies.

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