The galaxies in our universe are organized into galactic clusters, and these clusters contain some dead galaxies which have stopped forming stars. New research reveals that these “red and dead” galaxies can be brought back to life by giant cosmic tsunamis.
Published in the journal Monthly Notices of the Royal Astronomical Society, this new information was unearthed when astrophysicists Andra Stroe of Leiden Observatory and David Sobral of Leiden and the University of Lisbon observed the merging galaxy cluster CIZA J2242.8+5301 (nicknamed the “Sausage”) located 2.3 billion light-years away.
The observations were made using the Isaac Newton and William Herschel Telescopes on La Palma, and the Subaru, CFHT and Keck Telescopes on Hawaii. Stroe and Sobral found that the cluster galaxies were transformed by a shock wave, triggering a new wave of star formation.
This phenomenon can be explained by comparing galactic clusters to cities. According to this analogy, thousands of galaxies can be part of these “cities.” Over the course of billions of years, some of these clusters merge with others – like growing cities absorbing nearby towns. When galactic clusters collide, it generates a huge shock wave of energy which, in this case, is moving at an astonishing speed of 9 million kilometers (6 million miles) per hour. This newly released energy, the cosmic tsunamis, can aid in or drive the process of the birth of new stars.
The tsunami, by causing turbulence in the galactic gas, triggers an avalanche-like collapse that eventually leads to the formation of very dense, cold gas clouds. These are vital for the formation of new stars, and are what essentially bring galaxies back from the dead.
“Star formation at this rate leads to a lot of massive, short-lived stars coming into being, which explode as supernovae a few million years later,” Sobral said in a statement. “The explosions drive huge amounts of gas out of the galaxies and with most of the rest consumed in star formation, the galaxies soon run out of fuel. If you wait long enough, the cluster mergers make the galaxies even more red and dead – they slip back into a coma and have little prospect of a second resurrection.”
The phenomenon of cosmic tsunamis was well-known among the scientific community. However, there was a lack of concrete evidence that it affected galaxies themselves.
“We assumed that the galaxies would be on the sidelines for this act, but it turns out they have a leading role. The comatose galaxies in the Sausage cluster are coming back to life, with stars forming at a tremendous rate. When we first saw this in the data, we simply couldn’t believe what it was telling us,” Stroe said.
The collision of the clusters occurred one billion years ago, but the scientists are observing this event now due to the unimaginably massive distances between those galaxies and ours.
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