Cosmic tsunami for sleeping galaxy

Galaxies in a coma can come back to life. If there is a fusion of galaxy clusters that generates a shock wave capable of generating a new season of star formation.
The galaxies are grouped often in clusters, and many are close to us but have stopped forming stars in the distant past. An international team of astronomers, led by Andra Stroe of Leiden Observatory and David Sobral of Leiden and the University of Lisbon, they found that these galaxies in a coma can come back to life. If there is a fusion between galaxy clusters, it generates a huge shock wave, which can result in the birth of a new generation of stars. These events can provide a vital boost to new galaxies dormant. This study was published in the journal Monthly Notices of the Royal Astronomical Society.


Credit: Andra Stroe

Galaxy clusters are like cities, where thousands of galaxies can be crowded, at least if we compare the clusters to the space around them, sparsely populated. Over billions of years have built the structure of the universe merging with adjacent clusters, just as the growing city absorb the surrounding cities. When this happens, there is a clash between clusters and a huge release of energy. The shock wave travels through the clutter like a real tsunami, but until now there was no evidence that the galaxies they were directly affected.
Stroe and Sobral have observed the merger of galaxies in the cluster Ciza J2242.8 + 5301, nicknamed the “sausage”, located 2.3 billion light-years away in the constellation of the Lizard, in the northern sky. To conduct their studies have used telescopes Isaac Newton and William Herschel of La Palma, the Subaru, the Canada France Hawaii Telescope and the Keck Observatory in Hawaii. The data will have discovered that galaxies have been profoundly transformed by the shock wave, triggering a new wave of star formation.
Stroe said: “In the past we have always assumed that galaxies were in the sidelines in these phases, and now we find that they have a major role. The galaxies in the cluster in a coma “sausage” are coming back to life, with stars in formation at an incredible pace. When we saw for the first time these data, we could not believe what we were showing. ”
This finding implies that the merger of galaxy clusters has a strong impact on the formation of stars. “Just like a spoon stirring a cup of coffee, these shock waves bring turbulence in the galactic gas. The turbulence in turn triggers an internal collapse, which eventually leads to the formation of very dense clouds and cold, vital for the formation of new stars, “says Stroe.


Credit: Andra Stroe

Sobral adds: “A similar rate of star formation leads to the emergence of a lot of massive stars, which typically have short lives and explode as supernovas a few million years later. Explosions push huge amounts of gas out of the galaxy, and considering that a large part of the gas is consumed by star formation, it is easy to understand why the galaxies run out soon their fuel. If you wait long enough, you look like mergers cluster galaxies make more and more red and lifeless, bringing them back to a state of coma from which are unlikely to wake up again. ”
Each cluster of galaxies in the universe close has experienced a series of mergers during his lifetime, so they should have crossed all a production period of extremely intense star. Since, however, the shock waves result in an increase of short duration (in astronomical terms) of star formation, astronomers have to be very lucky to be able to observe the cluster in the exact moment when its galaxies are “enlightened” by this violent episode.
The next step is to understand if the cluster “sausage” is somehow unique, or whether these bursts of star formation need special conditions to take place. Studying a much larger sample of galaxies, the team hopes to uncover new details about how these events occur.

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