Cosmic Michelangelo! NASA's Great Observatories Mosaic of Milky Way's Center & Massive Black Hole

No, it's not a lost Michelangelo masterpiece -it’s a mosaic of the sky 38 x 14 arc minutes across, or about half the size of the full Moon, of the core central region of our 400 million solar-mass galaxy. The bright white spot just to the right of the center behind light years of dust and gas is the monster SagA* -a black hole with four million times the mass of the Sun.

In celebration of the International Year of Astronomy 2009, NASA's Great Observatories — the Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra X-ray Observatory — collaborated to produce an unprecedented image of the central region of our Milky Way galaxy using infrared light and X-ray light to see through the obscuring dust and reveal the intense activity near the galactic core. The center of the galaxy is located within the bright white region to the right of and just below the middle of the image. Each telescope's contribution is presented in a different color:

- Yellow represents the near-infrared observations of Hubble. These observations outline the energetic regions where stars are being born as well as reveal hundreds of thousands of stars.

- Red represents the infrared observations of Spitzer. The radiation and winds from stars create glowing dust clouds that exhibit complex structures from compact, spherical globules to long, stringy filaments.

- Blue and violet represent the X-ray observations of Chandra. X-rays are emitted by gas heated to millions of degrees by stellar explosions and by outflows from the supermassive black hole in the galaxy's center. The bright blue blob on the left side is emission from a double star system containing either a neutron star or a black hole.

When these views are brought together, this composite image provides one of the most detailed views ever of our galaxy's mysterious core.

Although it is difficult to to give a precise estimate of the number of black holes that exist because not enough is known about the number of stars that become black holes, astronmers estimate that there is about one black hole for every 10,000 stars, which means that the Milky Way contains at least 100 million black holes. At the very center of the galaxy lurks the darth-vader rock star, the supermassive black hole shown above, Sagittarius A aka Sgr A*.

Looming beyond the horizon of Sgr A*, if we assume Einstein's theory of relativity that predicts what happens when a star collapses is correct, is a singularity. But it is a singularity that lies in the future rather than in the past, much like the Big Bang, only in reverse.

For the first time, NASA's Chandra Observatory has resolved the complex structures at the center of our Milky Way galaxy through X-ray observations. Chandra astronomers reported that In addition to the supermassive black hole, Sgr A*, they have found the remains of a supernova that exploded some 10,000 years ago. The proximity of the supernova known as Sgr A East to the black hole in the galactic center suggests that the explosion may have prevented material from falling into the black hole, thus "starving" the supermassive black hole for a period of time.

This Chandra image of Sagittarius A* or Sgr A*, was made from the longest X-ray exposure of that region to date. In addition to Sgr A* more than two thousand other X-ray sources were detected in the region, making this one of the richest fields ever observed.

During a two-week observation period, Sgr A* flared up in X-ray intensity half a dozen or more times. The cause of these outbursts is not understood, but the rapidity with which they rise and fall indicates that they are occurring near the event horizon, or point of no return, around the black hole. Even during the flares the intensity of the X-ray emission from the vicinity of the black hole is relatively weak. This suggests that Sgr A*, weighing in at 3 million times the mass of the Sun, is a starved black hole, possibly because explosive events in the past have cleared much of the gas from around it.

Evidence for such explosions was revealed in the image - huge lobes of 20 million-degree Centigrade gas (the red loops in the image at approximately the 2 o'clock and 7 o'clock positions) that extend over dozens of light years on either side of the black hole. They indicate that enormous explosions occurred several times over the last ten thousand years.

Further analysis of the Sgr A* image is expected to give astronomers a much better understanding of how the Sgr* grows and how it interacts with its environment. This knowledge will also help to understand the origin and evolution of even larger supermassive black holes found in the centers of other galaxies.

Black holes are already well understood, we think, but we've only ever observed them at second hand - the behavior of orbiting objects or bent light rays. To actually view the shadow of a black hole, the cut-off point where light is swallowed and cannot escape, would be a massive advance - and only the beginning.

Detailed observation of the area around the Sag A* border would be a goldmine of information. The spin and rate of matter inflow into the central black hole will tell us about the Milky Way's creation, as well as providing further extreme tests of general relativity. We could even see frame dragging, which sounds like a video game hardware issue but is actually something that could happen to reality - where a spinning black hole grabs hold of space and literally pulls reality around after it.

Casey Kazan.

http://hubblesite.org/newscenter/archive/releases/2009/28/image/a/