Though it is a mere 25,000 light-years from Earth, the center of our own galaxy has long been one of the universe's most mysterious places. It's so full of dust and gas that visual telescopes, even those that can gather light from the most distant reaches of space, haven't been able to see inside.
to most astronomers because only one photon in a trillion can break
through," said Mark Morris, a professor of astronomy at UCLA who has spent
much of the last two decades probing the Milky Way's center with
telescopes that do not detect visible light but pick up electromagnetic
radiation emitted in radio, infrared and X-ray wavelengths.
Those images have offered
tantalizing but vague hints. When X-ray telescopes first peered at the
center of the Milky Way about 20 years ago, they found the area gave off a
massive X-ray glow. Recent evidence has pointed to a super-massive black
hole in the galaxy's center. X-rays, a highly energetic form of light, are
emitted from some of nature's most violent creations: supernova blasts and
black holes. But astronomers didn't know exactly what fearsome objects, if
any, emitted the X-rays. The first pictures in the 1980s, from an X-ray
telescope called Einstein, were low resolution and too fuzzy. They showed
only a diffuse glow of X-rays over a large area. Because X-rays are also
created at extremely high temperatures, many astronomers suggested the
center of the galaxy was filled with a huge, searing ball of
Now, a modern X-ray telescope 100 times more sensitive than
its predecessor has given the first clear glimpse of the Milky Way's
"We thought the image would be fantastic, but it's better
than we thought," said Q. Daniel Wang, the assistant professor of
astronomy at the University of Massachusetts at Amherst who led the team
mapping the galactic center.
The image shows that the X-rays don't
come from hot gas but from about 1,000 points of light, a vast collection
of what appear to be glittering star remnants, plus black holes. (Black
holes give off X-rays when they swallow big chunks of matter or other
"Our galaxy is like a big city," said Wang. "The center of
the galaxy is downtown, where the action is."
The finding from
NASA's $1.5-billion Chandra X-ray telescope provides more evidence of how
advances in technology in recent years are resolving decades-old mysteries
about the skies.
The results "finally settle important aspects of
the 20-year-old debate surrounding the origin of X-ray emission" from the
galaxy's center, said Andreas Eckart, an astronomer at the University of
Cologne who studies the galactic center and helped confirm the existence
of the massive black hole located there.
The new image was unveiled
Wednesday at a national meeting of the American Astronomical Society in
Washington. It is also being published in today's issue of the journal
Calling the images "really fabulous," Morris said the
findings resolved problems he and other astronomers have long had in
explaining how enough super-hot gas to generate all the X-rays could be
continually created in the Milky Way.
"This relieves the pressure
on us to evoke outrageous events and circumstances," including nonstop
supernova explosions or gas traps created by magnetic fields, he
The X-rays appear to come from a bright but more mundane
collection of objects: hundreds of small, collapsed stellar remnants like
white dwarf and neutron stars and also the black holes created when bigger
The new map suggests that the center of the galaxy,
unlike the quiet suburb where Earth resides, is a violent place where
stars are forming, dying and exploding at furious rates and being buffeted
by supernova shock waves.
"It's a nice place to visit with a
telescope, but I wouldn't want to live there," said Cordelia Lang, a
University of Massachusetts astronomer and coauthor of the new
The climate, though, is more benign than previously thought.
The hypothesis of a ball of hot gas would have required temperatures of
hundreds of millions of degrees. Instead, said Eric Gotthelf, a coauthor
of the study from Columbia University, "it's only a relatively mild 10
Studying our own galaxy is likely to help
astronomers understand the workings of all galaxies, how they formed and
why super-massive black holes seem to reside at the centers of many of
Our own largest black hole gives off a relatively weak X-ray
signal, although a team including UCLA's Morris did capture a "burp" last
year, a dramatic X-ray flare after the hole swallowed some
The study was not able to explain the diffuse X-ray glow
that remains or some small dust grains of iron that were
Eckart and Morris said the diffuse X-rays and the iron
may have been emitted by the black hole in a tremendous flash of energy as
recently as a few hundred years ago.