Astronomers take closest look ever at black hole's edge in Milky Way

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Washington, September 4 : By combining telescopes in Hawaii, Arizona, and California, astronomers have taken the closest look ever at the giant black hole in the center of the Milky Way.

They detected the structure at a tiny angular scale of 37 micro-arcseconds - the equivalent of a baseball seen on the surface of the moon, 240,000 miles distant. hese observations are among the highest resolution ever done in astronomy.

"This technique gives us an unmatched view of the region near the Milky Way's central black hole," said Sheperd Doeleman of MIT (Massachusetts Institute of Technology).

According to Jonathan Weintroub of the Harvard-Smithsonian Center for Astrophysics (CfA), "No one has seen such a fine-grained view of the galactic center before.

"We've observed nearly to the scale of the black hole event horizon - the region inside of which nothing, including light, can ever escape," he added.

Using a technique called Very Long Baseline Interferometry (VLBI), a team of astronomers, led by Doeleman, employed an array of telescopes to study radio waves coming from the object known as Sagittarius A (A-star).

In VLBI, signals from multiple telescopes are combined to create the equivalent of a single giant telescope, as large as the separation between the facilities.

As a result, VLBI yields exquisitely sharp resolution.

The Sagittarius A radio emission, at a wavelength of 1.3 mm, escapes the galactic center more easily than emissions at longer wavelengths, which tend to suffer from interstellar scattering. Such scattering acts like fog around a streetlamp, both dimming the light and blurring details.

VLBI is ordinarily limited to wavelengths of 3.5 mm and longer. However, using innovative instrumentation and analysis techniques, the team was able to tease out this remarkable result from 1.3-mm VLBI data.

The team clearly discerned structure with a 37 micro-arcsecond angular scale, which corresponds to a size of about 30 million miles (or about one-third the earth-sun distance) at the galactic center.

With three telescopes, the astronomers could only vaguely determine the shape of the emitting region.

Future investigations will help answer the question of what, precisely, they are seeing: a glowing corona around the black hole, an orbiting "hot spot," or a jet of material.

Nevertheless, their result represents the first time that observations have gotten down to the scale of the black hole itself, which has a "Schwarzschild radius" of 10 million miles.

"This pioneering paper demonstrates that such observations are feasible," commented theorist Avi Loeb of Harvard University. "It also opens up a new window for probing the structure of space and time near a black hole and testing Einstein's theory of gravity," he added.


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