HEASARC Staff Scientist Position - Applications are now being accepted for a Staff Scientist with significant experience and interest in the technical aspects of astrophysics research, to work in the High Energy Astrophysics Science Archive Research Center (HEASARC) at NASA Goddard Space Flight Center (GSFC) in Greenbelt, MD. Refer to the AAS Job register for full details.

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Introduction to Galaxies

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What are Galaxies?

Galaxies are made up of billions of stars that are gravitationally bound to eachother. Galaxies can be a spiral shape (like our own Milky Way) or elliptical or irregular. Galaxies tend to clump together in the universe, forming clusters of galaxies.

How does X-ray Astronomy Fit In?

Generally, the X-ray emission we see from other galaxies is from discrete sources such as X-ray binaries and supernova remnants. Our own galaxy is typical of this; we see the most and the brightest sources near the galactic center and in the galactic plane.

Recent results have shown that there is also an extended X-ray halo around some galaxies (particulary ellipticals) which extends well beyond the optical limits of these galaxies. This indicates the existence of diffuse hot gas and implies the existence of a halo of dark matter.

M31 in X-rays and optical light

On the left is a ROSAT PSPC mosaic of M31. On the right is an optical image obtained from the digitized sky survey of the Palomar plates using SkyView. Notice the X-ray sources in the ROSAT image that do not appear as optical sources in the Palomar image.


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Last modified: Thursday, 26-Jun-2003 13:48:46 EDT

HEASARC Staff Scientist Position - Applications are now being accepted for a Staff Scientist with significant experience and interest in the technical aspects of astrophysics research, to work in the High Energy Astrophysics Science Archive Research Center (HEASARC) at NASA Goddard Space Flight Center (GSFC) in Greenbelt, MD. Refer to the AAS Job register for full details.