PSPC Montage
Credit: M. F. Corcoran

Variable X-ray Emission of the Extremely Luminous Star Eta Carinae

At a distance of about 8500 light-years from Earth, Eta Carinae is one of the largest stars in our Galaxy. Eta Car probably contains as much mass as 100 suns, and puts out more energy each second than 1 million suns. Such stars are extremely rare in the cosmos. They have very short lives, punctuated by episodes of stellar "eruptions", mass ejections, and other violent instabilities, until they finally end their lives as huge, violent explosions called "supernovae" in which the energy of the blast eclipses the combined energy output of all the stars in the Milky Way.

Eta Car underwent a huge eruption in the mid-1800's, and recently it's showed signs of renewed activity. The star is a known source of extremely hot gas which produces X-ray emission, but the source of the X-ray emission has remained mysterious. In the early 1990's scientists at the Goddard Space Flight Center found a major clue to the origin of the X-ray emission by detecting for the first time variations in the amount of X-rays from the source. The picture above shows 4 false color images of the star taken by the ROSAT Positional Sensitive Proportional Counter. The left side of the picture represents images taken in the middle of 1992, while the right side shows images taken about 4 months later. The top half of the picture shows X-rays generated by gas at a temperature of 2 million degrees; the bottom half of the picture shows the image of the X-radiation from gas at about 20 million degrees. The emission from this extremely hot, 20 million degree gas increased by about a factor of 2 during this 4 month interval, while the emission from the cooler gas did not change during this time. Scientists have interpreted this variation to mean that Eta Carinae is not one star (as so long supposed) but two!

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Page Author: Dr. Michael F. Corcoran
Last modified September 27, 1999