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Using Europe’s Gaia Space Telescope, astronomers have identified 55 runaway stars being ejected at high speed from a densely packed young cluster in the Large Magellanic Cloud (LMC), a satellite galaxy of our own Milky Way. This is the first time that so many stars have escaped from a single star cluster.
The star cluster R136, located about 158,000 light-years away, is home to hundreds of thousands of stars and is located in a vast region of intense star formation in the LMC. It is home to some of the largest stars ever seen by astronomers, some with a mass of 300 times the Sun.
The runaway stars have been ejected in two outbursts over the past two million years. Some of them are running away from their homes at speeds of more than 100,000 km per hour – about 80 times faster than the speed of sound on Earth. The runaways, large enough to perish in supernovae and leave behind black holes or neutron stars, will act like cosmic rockets, exploding up to 1,000 light-years from their point of origin.
The discovery was made by a team of astronomers led by University of Amsterdam researcher Mitchel Stoop using Gaia, which accurately monitors the positions of billions of stars. The findings increase the number of known runaway stars by a factor of 10.
Related: Runaway ‘failed star’ races through the cosmos at a speed of 2 million km/hour
Scientists think stars have been banished from young star clusters like R136 – estimated to be less than 2 million years old (that may seem ancient, but compare it to our 4.6-year-old star clusters). billion-one year old solar system) – when crowded stellar newborns intersect and cause gravitational disruption of orbits. What surprised the team, however, was the revelation that more than one major escape had occurred in R136, and that the second occurred quite recently (at least in cosmic terms).
“The first episode occurred 1.8 million years ago, when the cluster formed, and is consistent with the ejection of stars during the cluster’s formation,” Stoop said in a statement. “The second episode was only 200,000 years ago and had very different characteristics.
“For example, the runaway stars from this second episode move more slowly and are not shot off in random directions as in the first episode, but in a preferred direction.”
These two episodes are believed to have caused R136 to launch as many as a third of its most massive stars in the past few million years.
“We think that the second episode of star blasting was due to the interaction of R136 with another nearby cluster that was only discovered in 2012,” team member and University of Amsterdam researcher Alex de Koter said in the statement. “The second episode may predict that the two clusters will mix and merge in the near future.”
Massive stars like those ejected from this young cluster can be millions of times brighter than the Sun, emitting much of their energy in the form of intense ultraviolet light. But this power comes at a price: Huge stars like this one burn through their nuclear fusion fuel quickly.
That means that while our sun will live for about 10 billion years, the lives of massive stars will end after just millions of years. The sun will end its life in a whimper and fade away as a cooling stellar remnant called a white dwarf, but these massive stars will extinguish with a bang and erupt in supernova explosions.
The Prima Donna star cluster is losing its star power
R136 is special not only because of its enormous population of massive stars; it is the prima donna cluster of the largest star birth region in space, located five million light years from Earth.
‘Now that we have discovered that a third of massive stars are expelled from their native regions early in their lives, and that they exert their influence beyond those regions, the impact of massive stars on the structure and evolution of galaxies is likely to be much greater. than previously thought,” says team member and researcher from the University of Amsterdam Lex Kaper in the same statement. ‘It is even possible that runaway stars formed in the early universe made an important contribution to the so-called reionization of the universe, caused by ultraviolet light.’
The reionization of the universe refers to a vital phase in cosmic evolution that occurred when the now 13.8 billion year old universe was still a baby, about a billion years old. At that time, light from early stars created bubbles of ionized gas in interstellar material. These ionized bubbles grew together with early galaxies, re-ionizing all the hydrogen by separating electrons from hydrogen nuclei. This marked the transition from the Cosmic Dawn period to a ‘mature’ cosmic stage that allowed for the evolution of ‘normal’ galaxies.
The main goal of the team’s research was to test the capabilities of Gaia, a European Space Agency mission tasked with collecting data to build a 3D map of the Milky Way. The LMC provides a good test because it is much further away than the stars Gaia usually studies in our own galaxy.
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“R136 has only just formed, 1.8 million years ago, and so the runaway stars cannot yet be so far away that it becomes impossible to identify them,” De Koter concludes. “If you can find many of those stars, you can make reliable statistical statements. This turned out beyond expectations and we are extremely happy with the results. Discovering something new is always exciting for a scientist.”
The team’s research was published October 9 in the journal Nature.