July 27, 2017

It Takes a Planet

Astronomers train an “Earth-sized” telescope, including UMass Amherst's LMT, on our galactic center

For five days recently, telescopes around the world—including UMass’s own Large Millimeter Telescope (LMT)—focused upon a supermassive black hole in the center of our galaxy. The black hole in question is Sagittarius A.

The interior of a black hole can’t be viewed because light cannot make it out, so instead the researchers imaged Sagittarius A’s (Sgr A) event horizon, the point past which nothing escapes a black hole’s devouring pull.

Although the gravitational force of Sgr A is equivalent to 4 million times the mass of our sun, the event horizon itself is relatively small. Due to that factor and to its great distance—27,000 light years away from us—a huge telescope would be needed to resolve the image: one as big as Earth.

So researchers did the next best thing, creating an array of radio telescopes spanning the globe, called the Event Horizon Telescope (EHT). Aiming each telescope at the same object over the course of many hours, their synchronized sampled curves resemble the observational effect of one large instrument.

Extreme environments make for extreme physics. “We’re probing regions that have such intense gravity that we cannot simulate it in any terrestrial labs,” says astronomy research professor Gopal Narayanan. “It’s one of the few times in astronomy when you can truly attack fundamental physics. We’re in a laboratory in which much of the outside noise is eliminated.

“This project is a testament to the collaborative nature of science. It involves scientists and engineers all across the world.”

Gopal Narayanan, Research Professor

“In astrophysics in particular, the place where you learn the most is at these limits. You approach a fundamental limit, something exotic and such extraordinarily high gravity like this, that’s where you learn if the theory you had is applicable.”

If predictions don’t prove right, it is, in a way, an even bigger opportunity: “If you talk to any scientist, they would love to see a fundamental theory proved to be right,” says Narayanan, “but they even love it more when a theory is proven wrong, because that gives us the opportunity to make a breakthrough in understanding. That’s where we make whole new strides.”

An Earth-sized endeavor to understand our galactic center creates a heady atmosphere. The LMT effort, led by Narayanan, included about 10 scientists and graduate students, including UMass graduate student Aleks Popstefanija, who has been involved in the project for the last two years. Teams observed for 16-hour stretches—switching out shifts—constantly communicating, encouraging, and assisting one another. 

“One hundred and fifty scientists, engineers, and support staff were involved at any given time during those five days, so if there was a technical problem at a site, they would try to find an expert at some other site who would have some idea of how to solve the problem, or assist remotely,” says Narayanan. The results will require months of computation, and the data from Antarctica, currently in austral winter, still awaits arrival. But if the mission succeeds, we will have the first real image of the black hole at the center of our galaxy.

“This project is a testament to the collaborative nature of science,” says Narayanan. “It involves scientists and engineers all across the world, coming from different cultural backgrounds. Was it difficult logistically? Yes. A lot of it is wrangling people together. But the scientific goal was clear. Different teams sitting on high altitude mountains, exhausted but wanting to make this work, calling another observatory and helping them out of their problems—that happened time and again in the EHT run. It speaks to the power of teamwork and collaboration. Science knows no borders.” 

Photography by Ana Torres Campos.
The image of the black hole is an artist’s rendition.