New study finds that supernova explosions and the jets of a monstrous black hole are
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scattering a galaxy’s star-making gas like a cosmic leaf blower. The findings, which relied on ultraviolet observations from NASA’s Galaxy Evolution Explorer and a host of other instruments, fill an important gap in the current understanding of galactic evolution. It has long been known that gas-rich spiral galaxies like our oun smash together to create elliptical galaxies such as the one observed in the study. These big, round galaxies have very little star formation. The reddish glow of aging stars comes to dominate the complexion of elliptical galaxies, so astronomers refer to them as “red and dead.” The process that drives the dramatic transformation from spiral galactic youth to elderly elliptical is the rapid loss of cool gas, the fuel from which new stars form. Supernova explosions can start the decline in star formation, and then shock waves from the supermassive black hole finish the job. Now astronomers think they have identified a recently merged galaxy where this gas loss has just gotten underway. The supermassive black holes that reside in the centers of galaxies can flare up when engorged by gas during galactic mergers. As a giant black hole feeds, colossal jets of matter shoot out from it, giving rise to what is known as an active galactic nucleus. According to theory, shock waves from these jets heat up and disperse the reservoirs of cold gas in elliptical galaxies, thus preventing new stars from taking shape. The galaxy NGC 3810 , shows signs of such a process. NGC 3810 is unique in that evidence of a past merger is clearly seen, and the shock waves from the central black hole’s jets have started to spread out very recently. The researchers used the Galaxy Evolution Explorer to determine the age of the galaxy’s stars and decipher its evolutionary history. The ultraviolet observations show that NGC 3810 ‘s star formation has petered out over the last 100 to 500 million years, demonstrating that the galaxy has indeed begun to leave behind its youthful years. The lack of many big, new, blue stars makes NGC 3810 look yellowish and reddish in visible light, and thus middle-aged.