Everything about The Galactic Center totally explained
The
Galactic Center is the rotational center of the
Milky Way galaxy. It is located about 7.6
kiloparsecs (24,800
LY) away from the
Earth, in the direction of the
constellation Sagittarius, where the Milky Way appears brightest. There is a
supermassive black hole at the Galactic Center of the
Milky Way.
Proof of existence and location
Because of cool
interstellar dust along the line of sight, the Galactic Center can't be studied at
visible,
ultraviolet or soft
X-ray wavelengths. The available information about the Galactic Center comes from observations at
gamma ray, hard X-ray,
infrared, sub-millimetre and
radio wavelengths.
Coordinates of Galactic Center were first found by
Harlow Shapley in his 1918 study of the distribution of the
globular clusters. In the
Equatorial coordinate system they are:
RA 17h45m40.04s,
Dec -29° 00' 28.1" (
J2000 epoch).
The complex
radio source Sagittarius A appears to be located almost exactly at the Galactic Center, and contains an intense compact radio source,
Sagittarius A*, which coincides with a
supermassive black hole at the center of our Galaxy.
Accretion of gas onto the
black hole, probably involving a
disk around it, would release energy to power the radio source, itself much larger than the black hole. The latter is too small to see with present instruments.
Stellar population
The central
parsec around Sagittarius A* contains thousands of
stars. Although most of them are old red
main sequence stars, the Galactic Center is also rich in
massive stars. More than 100
OB and
Wolf-Rayet stars have been identified there so far. They seem to have all been formed in a single
star formation event a few million years ago. The existence of these relatively young (though evolved) stars there was of a surprise to experts, who would have expected the
tidal forces from the central black-hole to prevent their formation. This
paradox of youth is even more remarkable for stars that are on very tight orbits around Sagittarius A*, such as
S2. The scenarios invoked to explain this formation involve either star formation in a massive
star cluster offset from the Galactic Center that would have migrated to its current location once formed, or star formation within a massive, compact gas
accretion disk around the central black-hole. It is interesting to note that most of these 100 young, massive stars seem to be concentrated within one (according to the
UCLA group
) or two (according to the
MPE group) disks, rather than randomly distributed within the central parsec. This observation however doesn't allow definite conclusions to be drawn at this point.
Star formation doesn't seem to be occurring currently at the Galactic center, although the
Circumnuclear Disk of molecular gas that orbits the Galactic center at two parsecs seems a fairly favorable site for star formation. Work presented in 2002 by Antony Stark and Chris Martin mapping the gas density in a 400
light year region around the galactic center has revealed an accumulating ring with a mass several million times that of the
Sun and near the critical density for
star formation. They predict that in approximately 200 million years there will be an episode of
starburst in the galactic center, with many stars forming rapidly and undergoing supernovae at a hundred times the current rate. The starburst may also be accompanied by the formation of
galactic jets as matter falls into the central
black hole. It is thought that the Milky Way undergoes a
starburst of this sort every 500 million years.
Further Information
Get more info on 'Galactic Center'.
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