You're in no danger of falling in,
but a large group of possible cosmic vacuum
cleaners have just been identified.
Researchers have come upon 26 possible
black holes in Andromeda, a galaxy near our
own.
This is the largest number of possible black
holes found in a galaxy outside the Milky
Way, but that may be because of
Andromeda's relative proximity to our galaxy.
It's probably easiest for Earth-based
scientists to find black holes outside the
Milky Way there, said Robin Barnard of the
Harvard-Smithsonian Center for Astrophysics
in Cambridge, Massachusetts.
Combining this discovery with previous
observations of nine other black hole
candidates, scientists can say that
Andromeda has a total of 35 possible black
holes. The research is published in The
Astrophysical Journal.
NASA's Chandra X-ray Observatory made
more than 150 observations over the course
of 13 years to identify these black hole
candidates.
Seven of the new potential Andromeda black
holes reside within 1,000 light years of the
center of that galaxy. This supports earlier
research showing that, near the center of
Andromeda, there are an unusual number of
X-ray sources.
Black holes can't be seen directly. But
astronomers can detect material falling into
them when they interfere with other stars.
A black hole is a dense region of space that
has collapsed in on itself in such a way that
nothing can escape it, not even light.
In a binary system of this nature, a black
hole and a star orbit each other closely.
Material from the star falls into the black
hole and "as it spirals in, it gets hotter and
hotter, and faster and faster, and eventually
it gives off X-rays, so we see lots and lots of
X-rays coming out of it," Barnard said.
The material as it has been swallowed gets
incredibly hot, up to about 10 billion degrees.
Because of the tremendous amount of energy
released, some of the brightest objects in the
universe are black holes.
It's hard for scientists to distinguish distant
black holes from neutron stars, however.
When a star explodes in a supernova, its fiery
death leaves behind either a neutron star or
a black hole, which is a more extreme version
of a neutron star.
If our own sun were a neutron star, it would
be only about 10 kilometers, or 6.2 miles,
across, Barnard said. By comparison, as a
black hole our sun might be only 2 kilometers
across. Black holes of the kind that scientists
may have spotted in Andromeda have masses
that are typically five to 10 times that of the
sun.
Neutron stars have a surface, so falling
material pounds onto it, Barnard said.
Material rains down at enormous speeds,
causing huge explosions and energy
emissions.
Billions of years from now, the Milky Way and
Andromeda galaxies will collide, marking the
end of the galaxy as we know it .
