Illustration of the hot halo around the Milky Way galaxy
Credit: NASA/CXC/M.Weiss/Ohio State/A Gupta et al

Spinning Hot Halo

We think galaxies may form through the accretion of huge amounts of matter from the intergalactic medium. As this matter falls together and accelerates, portions of it will collide, heating the gas to temperatures of millions of degrees. The combination of the total amount of matter accreted, its density, and its spin, helps determine the type of galaxy that's produced, whether spiral, elliptical, or irregular. After the galaxy is formed, the accreting gas that is left over forms a hot, large, massive halo around the galaxy. These halos are expected to be much larger than the galaxy, and very tenous, so it's difficult to directly detect them. But all our observations of external galaxies are seen through the halo surrounding the Milky Way, shown as the blue haze in the illustration above. Using the XMM-Newton X-ray Observatory, astronomers have been able to detect how the Milky Way's hot halo absorbs X-rays emitted from a selection of X-ray bright external galaxies distributed around the sky. By determining the Doppler motion of the Milky Way's halo through measuring the wavelengths of specific X-ray absorption features produced by atoms of oxygen in the halo, astronomers have revealed the motion of this hot gas. This study shows that the halo rotates at a remarkable speed of roughly 400,000 miles per hour, so that the spin of the halo is comparable to the spin of the Milky Way itself.
Published: August 1, 2016

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Page Author: Dr. Michael F. Corcoran
Last modified Monday, 08-Aug-2016 09:06:33 EDT