High-Speed Crash Makes Hot, 'Sterile' Galaxies

Oct. 9, 2008 -- A new wider view of two very well-known galaxies has revealed a big surprise: They are connected by faint, starless filaments of hydrogen gas which trace back to a very high-speed intergalactic collision.

The smash-up between galaxies M86 and NGC4438 not been suspected before, and may explain why M86, which is visible to the naked eye, is unable to give birth to new stars.

"Stars and gases behave very differently in collisions," explained astronomer Jeffrey Kenney of Yale University and lead author of a paper on the discovery in the Nov. 2008 issue of Astrophysical Journal Letters.

During galactic smash-ups stars rarely collide, since there is so much space between them. But gases do slam into gases. The faster the collision, the higher the temperature the gases reach.

In the case of M86, its gases are millions of degrees and radiate in X-rays. Until now, however, there was no easy explanation for all this blistering hot gas. The new evidence of M86's collision may solve that mystery.

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What's more, the super-hot gas also probably explains why M86 is unable to produce new stars. To make stars you need colossal clouds of frigid gas that will collapse to begin star-producing nuclear reactions.

Super-hot gases are far too agitated to clump together and collapse to form such new heavenly bodies. As a result, the wickedly hot galactic atmosphere of M86 leaves it bereft of baby stars and dominated by older stars that formed before something -- probably galactic gas collisions -- turned up the heat.