Scientists Hunt Down the Murderer of Galaxies: Strangulation

What kills galaxies and causes them to fade away over time? That's a good question and now, a new study reveals the method if not the murderer: strangulation.

There are two types of galaxies in the universe. Roughly half of them are "alive" galaxies, which produce stars. The other half are "dead" ones which have ceased star production. Galaxies that are alive, like our own Milky Way, are rich in cold gas-mostly hydrogen-which is needed to produce new stars. Dead galaxies, though, have very low supplies of this gas.

"Metals are a powerful tracer in the history of star formation: the more stars that are formed by a galaxy, the more metal content you'll see," said Yingjie Peng, one of the researchers, in a news release. "So looking at levels of metals in dead galaxies should be able to tell us how they did."

The scientists used data from the Sloan Digital Sky Survey to analyze metal levels in more than 26,000 average-sized galaxies. They found that it's likely that the dead galaxies were killed by strangulation.

"We found that for a given stellar mass, the metal content of a dead galaxy is significantly higher than a star-forming galaxy of similar mass," said Roberto Maiolino, co-author of the new study. "This isn't what we'd expect to see in the case of sudden gas removal, but is consistent with the strangulation scenario."

The findings are the first conclusive evidence that galaxies are being strangled to death. The researchers hope to find out exactly what causes this strangulation as the next step. While they have the method, they still have yet to track down the murderer.

The findings are published in the journal Nature.

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