Our galaxy takes center stage

Our galaxy takes center stage
X-ray mosaic shows unmatched detail at Milky Way’s center


A mosaic of several Chandra images of the central region of our Milky Way galaxy reveals hundreds of white dwarf stars, neutron stars and black holes bathed in glowing gas. The supermassive black hole at the center of the galaxy is located inside the bright white patch in the center. Click to launch a graphic presentation about X-ray astronomy and the Chandra telescope.

By Robert Roy Britt
SPACE.COM

WASHINGTON, Jan. 9 — A new mosaic of images produced by NASA’s Chandra X-ray Observatory reveals a stunningly crisp view of the chaotic center of our galaxy, where stars are born and die with remarkable frequency.

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“THERE ARE TONS of massive stars forming in the center of our galaxy,” said Q. Daniel Wang, a University of Massachusetts researcher who led the effort. Tons more are dead, having exploded and cast their shells into space.
X-rays pour out of both the cradles and the graves.
The new picture shows all this activity in unprecedented detail. Black holes and heavier-than-lead neutron stars make up just some of the nearly 1,000 newly found sources of X-rays seen in the image, Wang said, helping to solve a longstanding question about what was producing all the hot gas in the region that had only been seen as diffuse blobs.
Only about a dozen such X-ray sources were known before the new study.
Wang said more observations will be needed to figure out exactly which X-ray sources are black holes and which are neutron stars, for the energy they emit can seem quite similar.
The mosaic, released here Wednesday at a meeting of the American Astronomical Society, pieces together 30 separate X-ray images and covers an area of 400 by 900 light-years. The entire Milky Way galaxy is much wider, and we live near the outer edges of it, about 20,000 light-years from the center.

GETTING A GOOD VIEW
From this position in the galactic hinterlands, astronomers have long been frustrated by their poor view of the galaxy’s core. Intervening dust prevents good observations in visible light.
“Interstellar space is filthy,” said Columbia University’s David J. Helfand, who is leading a separate study to map the birth and death of large stars in the galaxy.

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But X-ray astronomy, which must be done from space-based observatories because most X-rays don’t penetrate Earth’s atmosphere, is rapidly opening the a window to the galactic center. And while the number of X-ray sources found in this latest study did not surprise researchers, it does verify their expectations and give them a host of new objects to study in greater detail.
The work, which is detailed in Thursday’s issue of the journal Nature, also provides a better view of how hot gas is distributed around the center of the galaxy. Helping to generate the gas and power all the starbirth and death is a central black hole, thought to contain the mass of nearly 3 million suns.
Wang and his colleagues say their research shows that, though the supermassive black hole is relatively quiet these days in terms of X-ray emissions, it may have been hundreds of times more energetic in the past. The study also showed that gas that had previously been expelled from the very center and is now moving outward is about 10 times cooler than thought.

WHAT THIS MEANS TO YOU

This gas, under pressure to escape, is blown out of the galactic center and flows beyond the main disk of the galaxy into a surrounding halo. Then it cools and settles in the outer galactic suburbs — where we live.
This flow of gas has been going on for billions of years and likely fueled the production of some of the chemical elements that are in your body, Wang said.
Seeing all this hot gas as it billows out of the galaxy’s midsection will help researchers understand what’s going on in there and in other galaxies.
“It’s a very high-pressure environment,” said Cornelia Lang, a postdoctoral researcher who helped produce the new view. “It’s a nice place to visit — with a telescope — but I wouldn’t want to live there.”
Eric Gotthelf of Columbia University also contributed to the work.

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