In a new survey, astronomers using the Hubble Space Telescope have managed to pinpoint the location of several Fast Radio Bursts (FRBs). FRBs are powerful rays of energy that until recently had mysterious, unknown origins. The research team, which includes Alexandra Manning and Sunil Simha from the University of California at Santa Cruz, and Wen-fai Fong from Northwestern University, conducted a survey of eight FRBs that found five of them to be spiraling out of line were poor in their host galaxies.
FRB sources are known to be difficult to locate because the bursts do not last very long and few repeat themselves, making follow-up observations incredibly difficult. The first FRB was seen in 2007 (although archival data searches revealed that an FRB was recorded by the Parkes Radio Observatory in Australia in July 2001). In the twenty years since then, about a thousand of them have been discovered – but only about 15 have identified their source.
Based on the observations available so far, the best hypothesis for the origin of FRBs is that they are generated by bursts of energy from magnetars. Magnetars are a type of neutron star (incredibly dense star nuclei that are left over from the collapse of supergiant stars) and are named after their strong magnetic fields. In 2020, an FRB was traced back to a magnetar, giving the hypothesis some solid evidence that was previously missing.
Hubble images show two galaxies from which FRBs originated (denoted by dotted ovals). On the right the images have been enhanced to show the spiral arms of the galaxies. Photo credits: NASA, ESA, Alexandra Mannings (UC Santa Cruz), Wen-fai Fong (northwest) Image processing: Alyssa Pagan (STScI)
This current research will help solidify the magnetar hypothesis further and rule out some other possible sources of FRB. For example, by finding that FRBs occur along galactic spiral arms, research shows that FRBs likely did not originate from the explosion of massive young stars that are clustering in brighter regions of the galaxies. It also rules out the merging of two neutron stars as an FRB source, since such events occur far from spiral arms and in much older galaxies. In contrast, magnetars can exist fairly easily within the galactic spiral arms observed by Hubble.
Photo credit: NASA’s Goddard Space Flight Center.
The research also helped confirm the types of galaxies that FRBs came from. Most large galaxies are accompanied by smaller dwarf galaxies (for example, the Milky Way is surrounded by around 50 smaller galaxies, such as the Small and Large Magellanic Clouds visible to the naked eye in the southern hemisphere). Previous attempts by ground-based telescopes to observe FRB sources failed to resolve the images clearly enough to determine whether the FRBs came from the main galaxy or a dwarf galaxy hidden behind it. The Hubble Space Telescope’s advantage over ground-based telescopes stems from its ability to observe distant galaxies without atmospheric distortion and to provide higher quality images. The Hubble poll concluded that the FRBs did indeed originate from the main galaxies and therefore that FRBs tend to originate from young, massive, star-forming galaxies.
“Our results are new and exciting,” stated lead author Alexandra Manning. “This is the first high-resolution view of a population of FRBs … Most galaxies are massive, relatively young, and are still forming stars. The imaging allows us to get a better idea of the overall properties of the host galaxy like mass and star formation rate and to study what exactly is happening at the FRB location because Hubble has such high resolution. “
The research will be published in an upcoming issue of the Astrophysical Journal.
“Hubble detects rapid radio bursts on the spiral arms of the galaxies.” NASA Goddard.