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Radio Astronomy - Watering Holes
11 April, 2005
The Search for Black
Holes Continues…
A group of Australian
and U.S. astronomers are returning to the Canberra Deep Space
Communication Complex (CDSCC) this winter in search of black
holes.
 Black holes are one of the most extreme objects
in the Universe. They are so massive that nothing, not even light,
can escape from them and this makes them hard to find. However,
it's what they do to their surroundings that gives them away.
Super-massive black holes are
believed to exist at the centres of some galaxies and it is thought
that many of them are surrounded by an orbiting disk of material
that has been attracted to the black hole and is slowly spiralling
in. This material is known as an accretion disk.
If this accretion disk contains
water vapour and conditions are just right, then water masers
will appear. Masers are a naturally occurring laser and can be
detected by radio telescopes. They make fantastic tracers of
the structure and motion of their environment.
Water masers in an accretion
disk are best seen when the disk is close to edge-on as seen
from Earth. When this happens the masers reveal a tell-tale,
triple-peaked spectral fingerprint and it is this that astronomers
are searching for. Once this  fingerprint is found it can reveal
information about the speed and shape of the disk, the mass of
the black hole and even an accurate measurement of the distance
from Earth.
By the time the maser emission
reaches us on Earth, the signals are very weak so large and sensitive
antennas are needed to detect them. The 70-metre antenna (Deep
Space Station 43) at Tidbinbilla is the largest and most sensitive
in the southern hemisphere for this type of work so a group of
Australian and US astronomers are surveying hundreds of galaxies
in search for black holes with DSS-43, as well as the Green Bank
Telescope located in West Virginia, USA.
So far 665 galaxies have been
observed and 16 new discoveries have been made, 11 at Tidbinbilla.
The observations are best done during the cold clear winter days
and nights and this winter will see the return of the survey
to CDSCC for hopefully another successful season.
Additional information can
be found on the web: SAMBA
Author:
Jim Lovell - Radio Astronomer |
