Michelle Starr
A recently discovered repeated ‘fast radio burst’ (FRB) called ‘FRB 20200120E’ further adds to the mystery of these already mysterious deep space signals.
Astronomers traced these bursts to a galaxy 11.7 million light-years from Earth, making it the closest known extragalactic fast radio burst; The signal is 40 times closer to us than the next closest extragalactic signal.
AN INCOMPATIBLE FRB
On the other hand, the signal is emanating from a very ancient globular cluster of stars where you wouldn’t expect to find a type of star that also emits FRBs into space.
The discovery of the signal suggests a different formation mechanism for these types of stars; this suggests that FRBs can occur in a more diverse range of environments than we thought.
FRBs have puzzled scientists since they were first discovered in 2007. They generate extremely strong signals emanating from deep regions of space millions of light-years away, some of which emit more energy than 500 million Suns, and are only detectable at radio wavelengths.
On the other hand, these explosions are surprisingly shorter than the blink of an eye—just a millisecond—and they are often not repeated; this makes it extremely difficult to predict, observe, and therefore understand explosions.
By examining the fine structure of these radio signals, especially dense celestial bodies like neutron stars, astronomers are trying to determine the type of celestial body they think might be causing them.
ALSO OBSERVED IN THE MILKWAY
There was a big leap forward in 2020. Finally, an FRB emitted by a magnetar* has been detected from inside the Milky Way Galaxy.
Magnetars, largely unconfirmed to date, are a rare variant of neutron star that arise from the collapsed core of a dead star between 8 and 30 times the mass of the Sun. Neutron stars are small and dense; It has a diameter of about 20 kilometers and a maximum mass of about two solar masses.
Magnetars, as the name suggests, add something else to the mix: it’s a truly insane magnetic field, about quadrillion times stronger than Earth’s magnetic field and a thousand times stronger than that of an average neutron star.
This data brings us back to the FRB 20200120E. It fits the profile perfectly, aside from the fact that it’s a rare example among FRBs – as it’s an FRB that repeats radio bursts.
However, because the signals were repeated, astronomers were more easily able to detect the region where they were formed in the vacuum of space. By analyzing other features contained in the signal, they were able to determine that it had traveled a relatively short distance.
EVEN IF THE LOCATION IS DETECTED, IT DOESN’T MATCH WITH WHAT WE KNOW
This has led researchers, with some uncertainty, to a large-scale spiral galaxy called ‘M81’, which was discovered in 2021. More precisely, the researchers think they traced FRB 20200120E to a globular-shaped cluster.
In a research paper published this week in the journal Nature, a team of astronomers confirmed this position.
That’s the point. Globular clusters are dense groups of stars that are very old and tend to be long-lived, as well as low-mass, no larger than the mass of the Sun. All of the stars in the cluster are believed to have formed at the same time in the same gas cloud; these clusters are like small towns, and these stars often spend their quiet lives together.
As we mentioned earlier, neutron stars consist of more massive stars that tend to have a shorter ‘main sequence’** lifetime (burning hydrogen); these are called ‘OB type stars’. So, as a general rule, you wouldn’t expect to encounter neutron stars or magnetars in a globular cluster.
“We report here that we have made observations that position the FRB in a globular cluster associated with M81, where it is 2 parsecs away from the optical center of the cluster,” the researchers write in their published paper.
“The spherical clusters host assemblages of ancient stars that challenge FRB models, reminiscent of young magnetars formed in a core collapse supernova.”
Don’t worry though; because there is an interesting example.
SO HOW DID THEY COME ABOUT?
Occasionally, a globular cluster is observed to host a type of neutron star known as the ‘millisecond pulsar’, which spins on its axis at extreme speeds. Because globular clusters are extremely densely populated, stars can interact and even collide with each other, then produce celestial bodies such as low-mass X-ray pairs and pulsars.
This also reveals different and intriguing mechanisms for a massive star to form a magnetar beyond a ‘core collapse supernova’, the research team said. A low-mass white dwarf interacting with and providing material from another star may gain enough mass to create a neutron star, or two white dwarfs may merge in the same direction.
The source of this FRB is likely to be a low-mass X-ray couple, such as a white dwarf and a neutron star, or a neutron star and an exoplanet, rather than a magnetar. It could even be a black hole that continues to grow.
We do not have conclusive evidence for these explanations—that is, no X-ray or gamma-ray activity that typically accompanies these systems—but they still cannot be ruled out.
Whatever the answer, the FRB 20200120E looks set to shake things up a lot. It will either teach us something new about stellar interactions in globular clusters or show us a new way of forming about FRBs.
Because it is a recurring FRB so close to us, it offers a rare opportunity to probe these enigmatic signals in detail.
The findings have been published in detail in the journal Nature.
*Magnetar is a kind of neutron star that obtains its radiant energy from its huge magnetic field. Such ‘pulsators’ emit very high energy x-rays and gamma rays.
**The ‘main sequence’ in astronomy [ing. main sequence], is the name given to a permanent and distinct group of stars that appear on star against flare color charts. Stars in this group are called ‘main sequence stars’ or ‘dwarf stars’. These are the most abundant stars in the universe, and the Sun is also included in this group.
Original article Science Alert taken from the website. (Translated by Tarkan Tufan)
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