A Mysterious Fast Radio Burst Has Been Detected Near Our Galaxy
M81 is one of the brightest galaxies in the night sky. It is home to a cluster of stars, located 11.74 million light-years from Earth, which recently emitted a particularly surprising burst of radio waves.
Fast radio bursts from around a nearby galaxy have just been detected. These repeated bursts of energy seem to come from an ancient stellar complex called a globular cluster. Surprisingly, this is the last region in which astronomers thought they would observe this kind of phenomenon.
Usually coming from billions of light-years away, these bursts of radio waves are extremely bright and brief . They are also called fast radio bursts or FRBs for fast radio burst . Detected for the first time in 2007 , the explanations around these phenomena are lacking. Based on observations so far, scientists suspect that they are emitted by young but short-lived stellar objects called magnetars.
But the sighting of a fast radio burst last year led researchers to a globular cluster nearly 11.7 million light-years from Earth, close to the neighboring spiral galaxy M81, according to a descriptive study of the discovery . Discovering this burst from a cluster of aging stars is like finding a smartphone embedded in a menhir: it doesn't make sense.
"This is clearly not a region where fast radio bursts are supposed to appear," tweeted Bryan Gaensler , an astronomer at the University of Toronto and co-author of the new study.
Explaining this strangeness is difficult. Scientists speculate that fast radio bursts could be produced in different ways, just like other celestial phenomena.
"FRBs could, [I emphasize], could, be a generic phenomenon associated with a whole host of sources," says Shami Chatterjee , an astronomer at Cornell University. He studies radio bursts but was not involved in this new discovery.
AN UNUSUAL PHENOMENON
It was in January 2020 that scientists first noticed the radio burst through the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. They called it FRB 20200120E. In recent years, this machine seems to be constantly detecting FRBs. When CHIME was commissioned in 2017 , scientists were only aware of thirty fast radio bursts. Today, thanks to the telescope, they count more than a hundred.
Like twelve other known bursts, FRB 20200120E has been called a "repeater". It is a kind of space engine that emits multiple, detectable bursts of radio waves , rather than a single intense emission. These bursts are not as bright as those coming from several billion light-years, in the distant cosmos. However, for a year, they have allowed scientists to identify the location of FRBs in space.
The team was thus able to attempt to identify a possible source. Measurements from the burst suggested that FRB 20200120E was quite close. Astronomers knew then that they were in pursuit of a local element, perhaps even within the gaseous and sparsely populated halo of the Milky Way. Subsequently, the scientists used a network of telescopes called the European Very Long Baseline Interferometry Network to precisely identify the location of the burst.
"In conclusion, we have proven that FRB 20200120E is associated with a globular cluster in the M81 galactic system, confirming that it is forty times closer than any other known extragalactic FRB," the authors write in the new study .
"It's very difficult to fit [these observations] with existing models," says Chatterjee.
Researchers are still trying to understand how globular clusters form. Some of these structures are formed during large collisions between galaxies but this observation cannot be extrapolated to all clusters.
Globular clusters are among the oldest objects in the observable Universe. They are billions of years old, as old - if not older - than the galaxies they orbit. Until now, scientists thought that fast radio bursts were produced by the youngest compact objects they had observed, magnetars. These are vivid stellar bodies with extremely strong magnetic fields. They are generated by the death of young massive stars when they explode. Once these stars form, the strength of their super-powerful magnetic field takes tens of thousands of years to decay, turning these stellar objects into an ordinary neutron star.
But based on current knowledge, glowing, densely populated globular clusters are not home to such tumultuous stars that collapse into magnetars.
"This type of star formation occurs throughout the universe, even within our galaxy, but not in globular clusters," said Claire Ye of Northwestern University, who studies globular clusters. “We wonder what can happen there! »
DENSE AND INTENSE STARS
It took nearly fifteen years for researchers to begin to unravel the mystery of fast radio bursts . Among the initial hypotheses on their origin, it is possible to cite the evaporation of black holes, the death of stars, the collision between dense objects and, of course, extraterrestrial technologies (spoiler: this is not about aliens ). Other clues, such as the nanometric structures found in radio bursts or their duration and intensity not exceeding the order of milliseconds, suggested that they could be produced by extremely dense compact objects.
Therefore, scientists turned to objects like black holes or neutron stars. They occur after the explosions of massive stars within supernovae. Some bursts were later found to come from regions with very strong magnetic fields , a new clue suggesting that they could be emitted by magnetars.
Last year, a magnetar within the Milky Way produced a radio burst similar to an FRB . It was slightly weaker than those from a completely different galaxy, but the scientists were confident they were on the right track .
"The model that FRBs come from magnetars gained momentum when we detected bursts similar to FRBs from a galactic magnetar," said Brian Metzger of Columbia University and the Flatiron Institute. “This was a situation where magnetars suited both theorists and observers. »
But this pattern was only short-lived. With the discovery of FRB 20200120E, astronomers must now determine whether magnetars emerge and survive in globular clusters. Otherwise, they need to understand if and how very old and very quiet stellar populations could generate such bursts. Neither of these two situations is easy to resolve.
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