Halo Clouds Spotted Around Colliding Galaxies
May 1, 2013

Chandra Provides Observations Of Massive Clouds Of Gas Around Colliding Galaxies

April Flowers for redOrbit.com - Your Universe Online

A detailed study of an enormous cloud of hot gas that envelops two large, colliding galaxies has been made using NASA´s Chandra X-ray Observatory. This oversized gas reservoir contains as much mass as 10 billion Suns, is 300,000 light years across, and radiates more than 7 million degrees Kelvin.

Scientists call this sort of cloud a “halo.” This particular halo is located in the system designated NGC 6240, which astronomers have long known is the site of the merger of two large spiral galaxies. These galaxies are each comparable in size to our own Milky Way, and each contains a supermassive black hole at its center. The black holes are spiraling in towards each other and may eventually merge to form a larger black hole.

As a consequence of the collision, the gas contained in each individual galaxy has been stirred up violently; causing a baby boom of new stars that has lasted for at least 200 million years. Some of the most massive stars raced through their evolution during this time and exploded relatively quickly into supernovas.

The research team argues that this rush of supernova explosions dispersed relatively high amounts of elements such as oxygen, neon, magnesium, and silicon into the gas envelop of the newly combined galaxies. This enriched gas has slowly expanded into and mixed with cooler gas already present, according to the data.

Shorter bursts of star formation occurred during the extended baby boom. The most recent burst occurred about 20 million years ago and lasted for about five million years. The team doesn´t think that this “short” burst was enough to produce the hot cloud of gas, however.

The authors suggest that the future of NGC 6240 will most likely see the two spiral galaxies form one young elliptical galaxy over the course of millions of years. They are unsure, however, how much of the gas will be retained by this new galaxy, and how much will be lost to space. The collision offers scientists the opportunity to witness a relatively nearby version of an event common in the early Universe when galaxies merged more often.

Chandra´s data were combined with optical data from the Hubble Space Telescope, showing long tidal tails from the merging galaxies. The findings of this study were published in the Astrophysical Journal.