Black Holes Light Up
Astronomers Spot Black Holes Using NASA's Chandra X-Ray Observatory
Not even light can escape a black hole's grip, but gas falling into a
black hole can heat up and become an intense source of X-rays, at
temperatures up to 1,000 times hotter than the sun. Astronomers use the
Chandra X-Ray Observatory -- a NASA satellite -- to map these X-ray
sources and study their properties
ANN ARBOR, Mich. -- They are deep and dense, and not even light can
escape their grip. We're talking about black holes, but they may not be
as dark as you think.
"If you have binoculars, you might be able to make out a smudge, which
would be the nearest galaxies," says Jon Miller, an assistant professor
of astronomy at the University of Michigan in Ann Arbor.
But what you won't see -- even with a telescope -- black holes! In fact,
Miller doesn't even use one to study black holes. He uses his computer.
"I think it's really for the best that NASA doesn't let people like me
drive billion-dollar satellites. So instead, we get data distributed
through the computer networks," Miller tells DBIS.
These data reveal just how complex black holes are. As gravity pulls
matter into the hole, it is heated 1,000-times hotter than the sun and
forms mega-heated gases. As the hole's magnetic field pulls these gases
into its center, it creates a light show.
Miller says, "Just before matter falls into the black hole, it can glow
very brightly in X-rays." The Chandra X-ray Observatory takes X-ray
photographs of these holes all over the universe.
According to Miller, every galaxy probably harbors a super massive black
hole at the center of that galaxy. "I mean something that's a million
or even billions of times the mass of our sun," he says. He hopes his
research will help to prove not only what happens after black holes are
formed, but also how they grow.
BACKGROUND: A team of astronomers
led by the University of Michigan may know how black holes are lighting
up the universe. New data from NASA's Chandra X-ray Observatory show for
the first time that powerful magnetic fields are the key to these
brilliant and startling light shows. By gaining deeper understanding of
how black holes gather matter into themselves, astronomers also hope to
learn more about other properties of black holes, including how they
grow.
LIGHT FROM DARK: Black holes are the darkest objects in the
universe. If a gas in a disk around a black hole loses energy, it will
swirl toward the black hole, generating light along the way. In 1973,
physicists suggested that magnetic fields could drive the generation of
light by black holes. They would do this by generating friction in the
gas and driving a wind from the disk that carries momentum outward. It
is estimated that up to half of the total radiation in the universe
since the Big Bang comes from material falling towards super-massive
black holes.
WHAT CHANDRA FOUND: Chandra measures the amount of X-rays
emitted at different energies, called X-ray spectroscopy. Spectroscopy
is the study of light's "fingerprint," according to its color, which
indicates its energy. Chemical elements each shine brightly at certain
energies, so scientists can determine the chemical composition of an
object. Chandra studied the X-ray spectra coming from a black hole
system known as J1655 located in the Milky Way galaxy. The black hole
was pulling material from a companion star into a disk, emitting the
telltale radiation. The Michigan astronomers showed that the speed and
density of the wind from the disk in J1655 corresponded to computer
simulation predictions for winds driven by magnetic fields.
ABOUT BLACK HOLES: A black hole forms when a massive star has
used up all its fuel. The reason the Sun and other stars emit light is
because trillions of nuclear reactions are taking place at the cores.
With core temperatures of millions of degrees, hydrogen atoms can
convert into helium atoms, emitting radiation in the process. At some
point, however, all the atoms are used up and no more nuclear fusion can
take place. Without that outward counter-force to the pull of gravity, a
star collapses inward, eventually reaching a point where the attractive
gravitational force is so strong, not even light can escape. No one has
ever observed the center of a black hole; until quite recently, such
objects only existed in theory. But scientists surmise that a black hole
has at its center an infinite density and an infinite gravitational
field, as well as infinite entropy, which means no further change can
take place. This is known as a "singularity." The event horizon of a
black hole is not so much a physical surface as the theoretical point of
no return for any object that gets caught in the black hole's powerful
gravitational field.
The American Astronomical Society contributed to the information contained in the TV portion of this report.Source: http://www.sciencedaily.com/news/space_time/astronomy/