When galaxies stop creating stars die in a slow process that extends for about four billion years and that is leaving the cold gas necessary to generate new stars.
This is the conclusion of a team of astronomers who investigated thousands of galaxies and deceased -vivas to assess whether this transition is fast or slow.
In the dead galaxies detected elevated levels of metals that accumulated during the process of star formation, and that point to a slow process of strangulation . The study was published in the journal “Nature”.
“Metals are a powerful indicator of the history of the formation of stars. The more stars are born in a galaxy, More metal can be detected, “said Peng Yingjie, a professor at the University of Cambridge and lead author of the study.
” In this way, observing the levels of metals in the dead galaxies could give us a clue how they died. “
If the death of a galaxy was swift and violent that is, if you saw the cold stripped gas allowing the formation of stars from internal causes or external-would cease immediately create stars and metal content would remain the same.
However, if the galaxy ceases to have their gas supplies but continues to use the one that fits, the metal would continue to increase until eventually, “suffocate “.
CO2 in humans, galaxies metal
Andrea Cattaneo, Observatoire de Paris in France, compared this evidence with the high dioxide levels carbon present in a human body strangled.
“For (the throttling process), they are used all the oxygen that remains in the lungs and continues to produce carbon dioxide, which is trapped in the body “Cattaneo said to Nature.
” Instead of accumulating CO2, the stifled galaxies accumulate heavier than helium produced by giant stars “-elements metals.
The team He led by Peng discovered the accumulation of metals by comparing the spectrum of light emitted by 23,000 passive red galaxies with 4,000 blue galaxies were forming stars.
The researchers used data from the Sloan Digital Sky Survey, a vast Detailed and colorful collection of images covering a third of the sky that has been used to compile an accurate 3D map of the universe.
Suspects
On average , live galaxies were four billion years younger than the dead.
According to the calculations of the astronomers, this is equivalent to the time that the galaxies needed to burn the gas that remains in the strangulation .
It is considerably longer than the four minutes it takes for the body to die for the same cause within, but the analogy holds.
“This is the first conclusive evidence that galaxies are being strangled until they die, “says Peng.
” The next step is to understand what causes this process. In essence, we know the cause of death, but we do not know who the murderer is, but we have some suspects. “
One of the possible culprits is overpopulation. If a galaxy is in a large group, gathering gas from the surrounding environment can be affected and begin the process of strangulation.
Among the clusters of galaxies, astronomers saw even more pronounced differences in metal content, which It gives more weight to this idea.
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