Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

February 27, 1996

X-ray Moon and X-ray Star

Explanation: An X-ray star winks out behind the Moon in these before and after views of a lunar occultation of the galactic X-ray source designated GX5-1. The false color images were made using data from the ROSAT orbiting observatory and show high energy X-rays in yellow (mostly from GX5-1), and lower energy X-rays in red (the Moon reflecting X-rays from the Sun). GX5-1 is a binary system consisting of a neutron star and a companion star in mutual orbit about the system's center of mass. The gas in the companion star's outer envelope falls toward the neutron star and accumulates in a disk around it. This disk material swirls deeper in to the neutron star's gravitational well, and is finally dumped onto its surface - in the process creating tremendous temperatures and generating the high energy X-rays.

Tomorrow's picture: Explosions Discovered Near Galactic Center

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Authors & editors: Robert Nemiroff (GMU) & Jerry Bonnell (USRA).
NASA Technical Rep.: Sherri Calvo. Specific rights apply.
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