Scientists have discovered that bizarre cosmic phenomena known as fast radio bursts are more likely to occur in huge galaxies than in smaller ones, in turn unraveling the secrets of how so-called magnetars form.
Fast radio bursts (FRBs), which are brief, intense bursts of radio waves originating from outer space, were first discovered in 2007, and are thought to be caused by highly magnetized neutron stars called magnetars.
Now, according to a new paper in the journal Nature, FRBs are more likely to be seen in enormous star-forming galaxies than in lower-mass galaxies. This suggests that magnetars themselves may form as a result of two stars merging together and then exploding in an enormous supernova.
"The immense power output of magnetars makes them some of the most fascinating and extreme objects in the universe," paper co-author Kritti Sharma, a graduate student at Caltech, said in a statement. "Very little is known about what causes the formation of magnetars upon the death of massive stars. Our work helps to answer this question."
FRBs typically last only a few milliseconds, but despite their short duration, they are incredibly powerful, sometimes releasing more energy in a few milliseconds than the sun does in an entire day. The origins of these bursts of energy have mystified scientists for years, but recent research has strongly suggested that magnetars may be responsible.
Magnetars are a rare type of neutron star with an extraordinarily powerful magnetic field 100 trillion times stronger than Earth's. Neutron stars themselves are the remnants of massive stars that exploded in supernovae and then collapsed, packing an immense amount of matter into a small, dense core. Magnetars are a specific, highly magnetized form of neutron star that can emit intense bursts of radiation.
Magnetars were one of the main candidates for the sources of FRBs, given their ability to release large amounts of energy in short timescales. In 2020, another Nature paper revealed that an FRB was detected from within our own galaxy for the first time, coming from a known magnetar, strengthening the theory that magnetars could be responsible for at least some FRBs.
According to the new Nature paper, the Caltech researchers used a radio array named the Deep Synoptic Array-110 (DSA-110) to analyze the galaxy of origin of 30 FRBs around the observable universe.
"DSA-110 has more than doubled the number of FRBs with known host galaxies," co-author Vikram Ravi, an assistant professor of astronomy at Caltech, said in the statement. "This is what we built the array to do."
They discovered that FRBs are more common in massive star-forming galaxies than in lower-mass star-forming galaxies. This was surprising, as the researchers previously thought that FRBs occurred equally in all types of galaxies. This also suggests that if FRBs are more common in massive galaxies, so are magnetars.
In April 2020, @NASA missions helped establish that the first fast radio burst seen within our Milky Way galaxy came from a magnetar. A magnetar is a type of isolated neutron star with city-sized remains of a star many times more massive than our Sun. https://t.co/eA8WmYUJlk pic.twitter.com/VM4higtI6J
— NASA Universe (@NASAUniverse) November 4, 2020Massive galaxies tend to be more rich in metal—as these metals are made by stars and scattered when they explode in a supernova.
"Over time, as galaxies grow, successive generations of stars enrich galaxies with metals as they evolve and die," Ravi said
Metal-rich stars tend to grow much larger than stars without metals, and larger stars usually die in a supernova rather than fading into obscurity. Massive stars are also usually found in binaries, and can steal material from the other, potentially leading to the two stars merging.
"A star with more metal content puffs up, drives mass transfer, culminating in a merger, thus forming an even more massive star with a total magnetic field greater than what the individual star would have had," Sharma explained.
Therefore, as FRBs are more common in metal-rich galaxies, magnetars are also forming in this metal-rich environment, which is known to promote the merging of stars, suggesting that magnetars may originate from stellar mergers.
"This result is a milestone for the whole DSA team. A lot of the authors on this paper helped build the DSA-110," Ravi said. "And the fact that the DSA-110 is so good at localizing FRBs bodes well for the success of DSA-2000."
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References
Sharma, K., Ravi, V., Connor, L., Law, C., Ocker, S. K., Sherman, M., Kosogorov, N., Faber, J., Hallinan, G., Harnach, C., Hellbourg, G., Hobbs, R., Hodge, D., Hodges, M., Lamb, J., Rasmussen, P., Somalwar, J., Weinreb, S., Woody, D., . . . Yao, Y. (2024). Preferential occurrence of fast radio bursts in massive star-forming galaxies. Nature, 635(8037), 61–66. https://doi.org/10.1038/s41586-024-08074-9
Bochenek, C. D., Ravi, V., Belov, K. V., Hallinan, G., Kocz, J., Kulkarni, S. R., & McKenna, D. L. (2020). A fast radio burst associated with a Galactic magnetar. Nature, 587(7832), 59–62. https://doi.org/10.1038/s41586-020-2872-x
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