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Observations of the Galactic Core |
Visual Observations
Walter Baade started using the 18-in Schmidt telescope at Mount
Palomar in 1937 soon after it was completed. He attempted to
penetrate the heavy interstellar extinction near the Galactic
center by using panchromatic films and deep red filters (Osterbrock
2001). Baade was unable to observe the Galactic center itself,
but he found regions of less obscuration close to the heart of
the Milky Way, including “Baade’s window,” which is centered
around NGC 6522 in Sagittarius (Osterbrock 2001; Moore 2002).
These regions of less obscuration permit visual and near
infrared observation of RR Lyrae stars, Mira variables, and
other types of stars in the Galactic bulge relatively close to
the Galactic core. Observation of such stars provides another
method besides those of Shapley and Oort for measuring the
distance to the Galactic center. The observed brightness of
these stars near the Galactic center can be corrected for
interstellar extinction and then compared to their known
intrinsic luminosities, thus permitting the distance to the
Galactic center to be estimated.Infrared and Radio
Observations; The Black Hole at the Galactic Center
Observations of the Galactic center at infrared and radio
wavelengths show a very complex structure. These observations
are possible because long wavelengths readily penetrate through
the obscuring dust and gas between the Solar System and the
Galactic center. Radio and infrared observations are also
complemented by observations of the Galactic center at very
short wavelengths in X-ray and gamma ray frequencies (NRL 2003;
Baganoff 2003).
At the very center of the Milky Way, there is a complex of hot
dense molecular clouds 14 parsecs in diameter which partially
surrounds an inner most star cluster (Spark and Gallagher 2000).
This complex of molecular clouds, Sagittarius A (Sgr A), is the
strongest radio source in the Galactic plane near the Galactic
center. In 1974 Balick and Brown reported “(t)he detection of
strong radio emission from [a] bright…unresolved…structure in
the inner 1 pc core of the galactic nucleus…” This is now called
Sagittarius A* (Sgr A*) to distinguish it from Sagittarius A
that surrounds it (Balick and Brown 1974; Science NASA 2002).
Sagittarius A* is contiguous to the inner most star cluster. |
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