Scientists have discovered that dead galaxies become "dead" as they no longer rapidly produce stars as these galaxies are choked to death by "strangulation" when they apparenly run out of stellar material for new star formation.

Compared to the Milky Way galaxy which is considered as a "living" galaxy, our galaxy is still abundant with star making gases such as hydrogen where this is considered to be the main ingredient for star formation. Dead galaxies on the other hand, have already run out of hydrogen.

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Now, this new study investigates where this gas has gone to and there are two theories that scientists adhere to when it comes to galactic deaths.

The first theory involves that this gas has been rapidly sucked away from the galaxy via internal or external forces that can include another passing galaxy with powerful gravitational forces that can instill a quick, galactic death.

The second theory involves a blocking from an unknown source of fresh, gas supplies almost literally choking the galaxy to death. 

Researchers have now analyzed data from 26,000 galaxies near the region of the Milky Way, detecting their metal levels inside them.

According to lead author Yingjie Peng from the University of Cambridge, metals are a very powerful indication of the galactic history of star formation. For example, the more metal inside that galaxy, more stars are churned out by that galaxy. This also means that observing the metal levels in the galaxy can reveal how they died.

Researchers point out that if a galaxy dies quickly by a loss of star forming gas, the metal formation inside them would also come to a quick stop. In another circumstance, if the galaxy slowly choked to death and withered away by a deprivation of essential gases, then metal levels will still continue to rise until the galaxy devours all the gas it still possesses. 

During this new survey, dead galaxies have higher amounts of metal compared to live galaxies that are still forming stars where this finding leads to stronger evidence of strangulation that occurs until they eventually die.

Peng adds that this marks the first conclusive evidence of galaxies getting strangled to death.

This strangulation apparently happens to massive galaxies that can hold 100 billion suns but for larger galaxies, there's still not enough evidence to pinpoint their deaths.

Tagsgalaxy deaths, galaxy strangulation, why do galaxies die, University of Cambridge, University of Cambridge