After studying a sequence of unusual brilliant flashes in a galaxy only 12 million light-years away, scientists had a peculiar case of déjà vu.
Repeating rapid radio bursts (FRBs) have an eerie resemblance to the flashes in the Crab Nebula. Several different cultures have described seeing the Crab Nebula around 1054 AD, making it one of the most well-documented relics of an ancient star explosion, or supernova. Scientists say the multicolored aftereffects show strong and vivid flashes similar to the newly discovered FRBs in the galaxy M81.
Kenzie Nimmo, a Ph.D. student in astronomy at the Netherlands Institute for Radio Astronomy and the University of Amsterdam in the Netherlands, stated in a statement, “Some of the signals we observed are short and extremely intense, just like some signals from the Crab pulsar” (opens in new tab).
The Chinese astronomers observed a new or “guest” star in the sky above the southern horn of Taurus on July 4, 1054, the day after the explosion that would eventually become the Crab Nebula. Astronomers observed this “guest” for 23 days, during which time its brightness was six times that of Venus. Arab and Japanese astronomers both recorded its continued visibility nearly two years after the explosion.
Due to its faintness, the surviving nebula wasn’t noticed until 1731, when British astronomer John Bevis used a telescope to study it for the first time. When the French astronomer Charles Messier made his own observations of the nebula 27 years later, he included it in his now-famous catalog of Messier objects and gave it the designation Messier 1 or M1.
Astronomers didn’t discover pulsars, a type of neutron star (itself a super-dense stellar corpse left by a supernova) with a strong magnetic field, until the 1960s, when they discovered a flickering radio emission that coincided with the location of the Crab Nebula.
Even while astronomers know what causes the bursts in the Crab Nebula, they still don’t know what’s going on in galaxy M81 despite the similarities between the two. First detected in January 2020, these FRBs were found to originate in the direction of the constellation Ursa Major, the Great Bear.
So far, FRBs have been identified almost exclusively in galaxies with young stars; however, the M81 sightings are an exception, as the signal’s origin was clearly localized to an ancient group of stars known as a globular cluster via a network of a dozen radio dishes.
Magnetars, the most powerful magnets in the universe and another form of supernova remnant, have been proposed as a possible source of FRBs. This explanation is straightforward in regions rich in young stars, but M81 presents some challenges, according to the astronomers.
According to the statement, “we expect magnetars to be shiny and young, and definitely not surrounded by old stars,” said Jason Hessels of the University of Amsterdam and ASTRON. “A magnetar cannot have originated from the explosion of a young star, as seen here. Another approach must exist.”
One theory suggests that a white dwarf (the smoldering core of a massive, extinguished star) sucked gas from an unlucky neighboring star. The physicists think that the white dwarf eventually collapsed into a magnetar due to the added mass.
Scientists aren’t sure what created the signal or why it’s so similar to the one coming from the Crab Nebula, but they suspect a peculiar magnetar, pulsar, or some other astronomical event. On February 23rd, two papers based on this study were published: one led by Nimmo, and the other led by Franz Kirsten of the Chalmers University of Technology and the Netherlands Institute for Radio Astronomy.