Reviewed by Victoria SmithNov 7 2024
According to a study published in Nature, a research team led by Caltech has discovered massive star-forming galaxies, not low-mass ones, are the universe’s most likely locations for fast radio bursts (FRBs).
Antennas of the Deep Synoptic Array-110 capture FRBs, revealing large host galaxies that challenge current models of FRB origins. Image Credit: Annie Mejia/Caltech
FRBs are extremely energetic pulses of radio-frequency light that have illuminated the sky repeatedly since their discovery in 2007. Astronomers have been desperate to unveil their origins.
The number of confirmed FRBs is in the hundreds, and scientists have gained increasing evidence for their triggers: magnetars—highly magnetized dead stars known as neutron stars.
The crucial evidence arose when a magnetar erupted in our galaxy. Several observatories captured the event in real-time.
This discovery has sparked new theories regarding magnetar formation. According to the study, these unusual dead stars, which have magnetic fields that are 100 trillion times stronger than Earth's, are frequently created when two stars combine and explode as supernovae.
It was previously unknown if magnetars could form when a single star exploded or due to the explosion of two merged stars.
The immense power output of magnetars makes them some of the most fascinating and extreme objects in the universe. Very little is known about what causes the formation of magnetars upon the death of massive stars. Our work helps to answer this question.
Kritti Sharma, Study Lead Author and Graduate Student, California Institute of Technology
The project started with a search for FRBs using the National Science Foundation-funded Caltech Deep Synoptic Array-110 (DSA-110) at the Owens Valley Radio Observatory near Bishop, California.
Only 23 FRBs have been localized by other telescopes, while 70 FRBs have been found and located in their particular galaxy of origin thus far by the extensive radio array. Thirty of these localized FRBs were examined by the researchers in the current study.
DSA-110 has more than doubled the number of FRBs with known host galaxies. This is what we built the array to do.
Vikram Ravi, Assistant Professor, Astronomy, California Institute of Technology
Despite FRBs occurring in star-forming galaxies, the team was surprised to discover that massive star-forming galaxies tend to experience FRBs more frequently than low-mass star-forming galaxies. Astronomers had previously believed that FRBs occurred in all types of active galaxies.
With this knowledge, the team began speculating what the findings would reveal about FRBs. Massive galaxies are usually metal-rich because metals—elements created by stars—take time to accumulate over cosmic history.
These metal-rich galaxies are more likely to have FRBs, which suggests they also have more magnetars, the source of FRBs.
Metal-rich stars—those that contain elements heavier than hydrogen and helium—grow larger than other stars.
Ravi added, “Over time, as galaxies grow, successive generations of stars enrich galaxies with metals as they evolve and die.”
Huge stars that explode in supernovae and can become magnetars are also more likely to be found in pairs.
Binaries account for 84 % of all massive stars, so when one massive star in a binary becomes puffed up due to excess metal content, the excess material is pulled over to its partner star, facilitating the two stars' eventual merger. These merged stars would have a stronger combined magnetic field than a single star.
Sharma added, “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.”
As FRBs are preferentially observed in massive and metal-rich star-forming galaxies, magnetars, which are thought to trigger FRBs, most likely form in metal-rich environments conducive to star merging. The findings suggest that magnetars throughout the universe are formed from the remnants of stellar mergers.
The team hopes to use DSA-110, followed by the DSA-2000 (a larger radio array built in the Nevada desert and completed in 2028), to locate more FRBs and their origins in the future.
“This result is a milestone for the whole DSA team. A lot of the authors on this paper helped build the DSA-110. And the fact that the DSA-110 is so good at localizing FRBs bodes well for the success of DSA-2000,” Ravi stated.
National Science Foundation funded the study.
Other authors from Caltech include Liam Connor, Casey Law, Stella Koch Ocker, Myles Sherman, Nikita Kosogorov, Jakob Faber, Gregg Hallinan, Charlie Harnach, Greg Hellbourg, Rick Hobbs, David Hodge, Mark Hodges, James Lamb, Paul Rasmussen, Jean Somalwar, Sander Weinreb, David Woody, Shreya Anand, Kaustav Kashyap Das, Yu-Jing Qin, Sam Rose, Dillon Z. Dong, Jessie Miller, and Yuhan Yao, as well as Joel Leja from The Pennsylvania State University.
Journal Reference:
Sharma, K. et. al. (2024) Preferential occurrence of fast radio bursts in massive star-forming galaxies. Nature. doi.org/10.1038/s41586-024-08074-9