For use with Chapter 30
Galaxy Has a Hole in It
November 13th, 2000
Artist's concept of a massive black hole and surrounding accretion
Milky Way is a spiral galaxy, which means the stars swirl
around a bulging, massive center. Our sun is located in an
outer region of one of the minor spiral arms. Decades ago,
scientists thought that the center of the galaxy was just
a grouping of stars.
at the University of California, Los Angeles, have confirmed
that there is a black hole in the center of the Milky Way.
This concept was speculated on for years, but it was only
recently when astronomers were able to pinpoint the location
of the black hole by observing the movement of orbiting stars.
The strong gravitational pull of the black hole dictates the
movements of neighboring stars.
black hole is a highly dense object. It has a lot of mass
packed into a small volume. Theoretically black holes are
singularities, which are large amounts of mass packed into
an infinitely small volume. With all of that mass in such
a tiny spot, the gravitational pull is enormous – so strong
that not even light can escape.
black holes give off no light, they cannot be "seen"
in the traditional sense. To observe the black hole, the researchers
were able to locate the center of the galaxy, known as Sagittarius
A, by detecting radio waves from that area. For years, it
has been speculated that this source of radio signals was
indeed a black hole. Then the researchers measured how other
stars and gases interacted with Sagittarius A. Black holes
can be detected by x-rays that are emitted as gas falls into
the black hole and is excited.
were able to study the velocities and trajectories of the
stars and gases surrounding Sagittarius A. They could also
study their centripetal acceleration as they spun around the
is theorized that the black hole at Sagittarius A could be
holding millions of stars within a very small volume – roughly
in an area that could fit within the orbit of Mars.
research gives scientists new insights into the structure
and formation of the galaxies. One of the main goals of using
a powerful X-ray observatory is to determine the existence
of black holes in other galaxies.
the Internet to investigate black holes and our galaxy. Record
this information in your Science Journal and draw a picture
depicting the black hole in the center of our galaxy.