We have detected a strange new signal across the chasm of time and space.
A repetition fast radio burst The source detected last year was recorded spitting out 1,863 bursts in 82 hours, out of a total of 91 hours of observation.
This hyperactive behavior has allowed scientists to characterize not only the galaxy that hosts the source and its distance from us, but also what the source is.
The object, named FRB 20201124A, was detected with the Five Hundred Meter Aperture Spherical Radio Telescope (FAST) in China and described in a new paper led by astronomer Heng Xu of Peking University in China.
So far most of the evidence points to a magnetar – a neutron star with extraordinarily strong magnetic fields – as a source of FRB emissions like this.
If FRB 20201124A is indeed from one of these savage cosmic beasts, it looks like an unusual specimen.
“These observations brought us back to the drawing board,” says astrophysicist Bing Zhang from the University of Nevada, Las Vegas.
“It is clear that FRBs are more mysterious than we imagined. Observational campaigns at multiple wavelengths are needed to uncover more of the nature of these objects.”
Fast radio bursts have been a source of perplexity for astronomers since their discovery 15 years ago, in archival data dating back to 2001: an incredibly powerful radio emission spike that lasts only the blink of an eye.
Since then, many more have been detected: bursts of radio waves lasting a millisecond, discharging at that time as much energy as 500 million suns.
Most recorded have only erupted once, making them difficult to study (let alone understand). A handful of them have been detected repeating, which has at least helped scientists trace them back to host galaxies.
Then, in 2020, a breakthrough. For the first time, a fast radio burst was detected in the Milky Way – leading astrophysicists to trace the phenomenon back to the activity of the magnetar.
This most recent extraordinary FRB example is another example of a rare repeater. In less than two months of observation, FRB 20201124A provided astronomers with the largest sample of fast radio burst data with polarization than any other FRB source.
Polarization refers to the orientation of light waves in three-dimensional space. By examining how much this orientation has changed since the light left its source, scientists can understand the environment it passed through. A strong polarization suggests a strong magnetic environment, for example.
Based on the wealth of data provided by FRB 20201124A, astronomers were able to deduce that the source is a magnetar.
But there was something strange. The way the polarization changed over time suggested that the strength of the magnetic field and the density of the particles around the magnetar fluctuated.
“I liken it to shooting a movie about the surroundings of an FRB source, and our movie revealed a complex, dynamically changing magnetized environment that had never been imagined before,” Zhang explains.
“Such an environment is not directly expected for an isolated magnetar. Something else could be near the FRB motor, perhaps a binary companion.”
This companion, according to the data, could be a hot blue Be-type star, which is often found in neutron star companions. The proof was presented in a separate documentled by astronomer Fayin Wang of Nanjing University in China.
But there was also something special.
As a type of neutron star, magnetars are the collapsed cores of massive stars which, having run out of fuel to burn and provide outward pressure, collapse under their own gravity.
Such stars burn up their fuel quickly and have a short life, expelling their outer material in a supernova when the core collapses.
Because their lives are so short, these young magnetars are thought to be in regions where star formation is still occurring. Stars live out their short lives and die, creating more clouds of matter to give birth to more stars. It is a beautiful cosmic circle of life.
But FRB 20201124A was found in a galaxy that looks a lot like the Milky Way. There’s not much star formation here at home, so there shouldn’t be any star baby booms near our unusual new friend FRB either.
FRB 20201124A is not the only FRB source to be found in a galaxy relatively devoid of star formation, however.
The growing number suggests there is vital information we may be missing, a hole in our understanding of FRB magnetars, how they form and where they reside.
But characterizing the source means we have a new place to look for answers. Wang and his colleagues’ work suggests that neutron star-Be star binaries may be one of the best places to look for fast radio burst-like signals.
Both articles were published in Nature and Nature Communication.