Explosive surprise at center of galaxy
By Ronald Kotulak
Tribune science reporter
January 10, 2002
Using a powerful new orbiting observatory, astronomers have
looked into the center of our Milky Way galaxy for the first
time, and what they saw looks pretty much like the grand finale
fireworks display on the 4th of July.
Picture this: The center is crammed with a sparkling array of
hundreds of white dwarf stars, neutron stars, black holes,
supernova explosions and new star formation with a supermassive
black hole at the center surrounded by a gigantic
10-million-degree cloud of dust that is blowing outward and
reaching us.
"This is a surprise--that the center of the galaxy has such a
rich structure," said Michael Turner, chairman of the University
of Chicago's astronomy department. "When you see more things you
can understand more."
Astronomers had suspected that the center contained a big black
hole, but they had no inkling of what was causing the enormous
amount of energy emanating from the galaxy's heart.
The new discovery shows the center to be a much more fearsome
place than anyone had ever suspected, as if some of the weirdest
and wildest objects of the universe came together in blazing
glory in the very same place.
"The central region is much more turbulent than I thought, much
more complicated, and there's a lot of mystery still there," said
Daniel Wang of the University of Massachusetts, who reported the
findings Wednesday at the American Astronomical Society meeting
in Washington, D.C. A published account of the findings appear
in the current issue of the British science journal Nature.
Looking into the heart of the galaxy has not been easy. The
inability to see what was going on there left astronomers
guessing about what made the nucleus tick.
The spiral-shaped Milky Way is about 80,000 light years across
and contains more than 100 billion stars. Our solar system is
some 26,000 light years from the center, but our line of sight to
the center is obscured by the huge dust cloud.
As a result, regular telescopes can't see the center. But X-rays
can because they pass through the dust.
Taking images with NASA's new Chandra X-ray Observatory, Wang,
along with Eric Gotthelf of Columbia University and UMass
postdoctoral researcher Cornelia Lang, got images that were 100
times sharper than those from radio or infrared telescopes and
the sharpest-ever images of the center, revealing hundreds of
X-ray-emitting white dwarf stars, neutron stars and black holes.
"For the first time we can now detect 1,000 energy sources at the
center of the galaxy compared to about a dozen sources that had
been previously known," Wang said in a telephone interview.
"We can now study how the environment around the center interacts
with the large black hole in the middle, and we can learn a great
deal about how these things actually work," he said.
The Chandra observatory was named after the late University of
Chicago theorist Subrahmanyan Chandrasekhar, who won the Nobel
Prize in physics in 1987 for his work on the physical processes
important for the structure and evolution of stars. The
observatory was launched into orbit in 1999.
"Without the X-ray eyes of Chandra, we would miss not only some
of the most exotic things going on in the universe, but the bulk
of the things going on," Turner said.
Unlocking galactic nuclei
The UMass discovery is helping to revolutionize our understanding
of the Milky Way's nucleus and it is the key to understanding all
other galactic nuclei in the universe, Andreas Eckert of the
University of Cologne, Germany, wrote in a Nature commentary.
The visible universe is thought to contain more than 100 billion
galaxies.
Wang likens the center of the universe to the downtown of a big
city surrounded by its neighborhoods and suburbs. "What happens
in the center of our galaxy matters because it affects not only
the center of the galaxy but the rest of the galaxy as well," he
said.
Not only could the new information help scientists understand the
mechanics of what makes the galaxy work, but it also could
provide more clues about the creation of our solar system and the
evolution of life.
It could even help foretell the future of our sun, since white
dwarfs are dying stars that were about the size of the sun but
have now shrunk to about the size of the earth. A spoonful of
material from a white dwarf weighs several tons.
Neutron stars were once the size of about three suns, but have
shrunk and condensed into a ball of neutrons about 12 miles in
diameter. A spoonful would weigh as much as Mt. Everest.
Universe's monsters
Black holes are the universe's monsters. Typically they form
when a star dozens of times larger than the sun explodes and the
leftover material condenses to an infinite density. The gravity
is so strong that not even light can escape. The humongous black
hole at the center of the galaxy is believed to be the size of 3
million suns.
"We don't know how this big black hole in the center formed, so
being able to more clearly see the most energetic things
happening there will help us understand its origin," Turner said.
Wang's findings indicate that the huge, superhot dust cloud at
the center is created by constantly exploding supernova. The
enormous heat and pressure created when a star explodes creates
all of the heavy elements from iron on up.
The cloud, which contains all of the elements that go into making
up planets and people, has been expanding outward since the birth
of the universe.
"The gas spreads out to the suburbs of the galaxy, including our
solar neighborhood, and it contributes to the basic elements
which appear in our bodies," Wang said.
