MIT-led Team Zooms in on Massive Black Hole at Center of Milky Way

Recently, an international team, led by astronomers at the MIT Haystack Observatory, obtained the closest views ever of what is believed to be a super-massive black hole at the center of the Milky Way galaxy.

The astronomers linked together radio dishes in Hawaii, Arizona and California to create a virtual telescope more than 2,800 miles across that is capable of seeing details more than 1,000 times finer than the Hubble Space Telescope.

The key to making these observations is a technique called very long baseline interferometry, or VLBI, which links simultaneous observations from several radio telescopes that can be thousands of miles apart. The signals from these radio dishes are combined to create a “virtual” telescope with the same resolving power as a single telescope as large as the distance between the participating dishes. As a result, VLBI can reveal exquisitely sharp details.

The cosmic target of the observations was the source known as Sagittarius A* (“A-star”), long thought to mark the position of a black hole whose mass is 4 million times that of the sun. Though Sagittarius A* was discovered three decades ago, the new observations for the first time have an angular resolution, or ability to observe small details, that is matched to the size of the black hole “event horizon” — the region inside of which nothing, including light, can ever escape.

The concept of black holes, objects so dense that their gravitational pull prevents anything including light itself from ever escaping their grasp, has long been hypothesized, but their existence has not yet been proved conclusively. Astronomers study black holes by detecting the light emitted by matter that heats up as it is pulled closer to the event horizon. By measuring the size of this glowing region at the Milky Way center, the new observations have revealed the highest density yet for the concentration of matter at the center of our galaxy, which “is important new evidence supporting the existence of black holes,” said Sheperd Doeleman of MIT, lead author of the study that will be published in the Sept. 4 issue of the journal Nature.

“This technique gives us an unmatched view of the region near the Milky Way’s central black hole,” Doeleman said. “The new observations have a resolution equivalent to being able to see, from Earth, a baseball on the surface of the moon.”

However, the team doesn’t have any actual images of the black hole—at least not yet.

“We don't have any images unfortunately,” Doeleman told The Daily Galaxy. “The VLBI experiment we did was capable of getting a size of SgrA*, but not its exact shape.”

But Doeleman says that getting actual visual images is now a possibility. 

“Now that we have shown that VLBI can detect the source, we can add more telescopes so that we can aim towards making images in the future.” Doelman explained to the Daily Galaxy.  “I note that even with the VLBI data we have, we can start to constrain models that people have made of how SgrA* radiates.

Though it takes light more than 25,000 years to reach us from the center of the Milky Way, the team measured the size of Sagittarius A* to be only one-third the Earth-sun distance — a trip that light would make in only three minutes. The astronomers concluded that the source of the radiation likely originates in either a disk of matter swirling in toward the black hole, or a high-speed jet of matter being ejected by the black hole. “Future observations that create even larger virtual telescopes will be able to pinpoint exactly what makes Sagittarius A* light up,” Doeleman said. “Most galaxies are now thought to have black holes at their centers, but because Sagittarius A* is in our own galaxy, it is our best chance to observe what’s happening at an event horizon.”

“This pioneering paper demonstrates that such observations are feasible,” commented theorist Avi Loeb of Harvard University, who was not a member of the discovery team. “It opens up a new window for probing the structure of space and time near a black hole and testing Einstein’s theory of gravity.”

Posted by  Rebecca Sato

* Potions of this post are extracts from an MIT News Office release written by David Chandler.

Comments

[EvilCosmicMonkey from Knoxville]

How big would such a black hole be ? Theoretically, we would only be able to see it because of the effects on its stellar brothers & sisters & the nearby dust & gas.

Enlighten me if this assumption is wrong.

[Yordan Yanakiev]

well .. actually there is a problem.
If they try to detect a super gravitation deforming object - like our black hole is - there could be a problem with actual returned data from weaves.
Weaves will be deformed and interferented by the black hole - due to speed and gravitation. And maybe we just read wrong data.

I think it will be best if Infrared and blue image from optical telescope is used along with data from radio telescopes - it will cut the error down.

[Hamy]

What happens if they discover that it is not spherical?

[EvilCosmicMonkey from Knoxville]

Yordan -

You're talking about a gravitational " lens ", right ?
I guess that's one way to " see " such an object, but readings on its true size would be distorted & off - scale.

Someone suggested that a black hole's mass might be INFINITE.

Hamy - A non - spherical black hole ? Could such a thing even exist ? ( Maybe if you count Rush Limbaugh & the commentators on Fox News..... )