Five Mysterious Fast Radio Bursts Tracked To The Spiral Arms Of Their Galaxies

Digitally enhanced images of FRB 190714, and FRB 180924. Image Credit: NASA, ESA, Alexandra Mannings (UC Santa Cruz), Wen-fai Fong (Northwestern)/Alyssa Pagan (STScI)

Fast radio bursts are extremely brief and powerful emissions of radio waves from beyond the Milky Way (usually). In just over a decade, 1,000 of them have been discovered but only a handful have been tracked to their galaxies of origin. Thanks to Hubble, we now can add five more to the latter group.  

In a thousandth of a second, FRBs generate as much energy as the Sun, but because they are so brief it's hard to trace back their origin, let alone what kind of object may have caused them. Locating these events gives us clues on what causes them. Now, astronomers have not only traced five FRBs to their host galaxies, but delivered the highest resolution images of those galaxies and the approximate location of the FRBs within the spiral arms of these cosmic islands. The incredible findings will be published in The Astrophysical Journal.

"Our results are new and exciting. This is the first high-resolution view of a population of FRBs, and Hubble reveals that five of them are localized near or on a galaxy's spiral arms," lead author Alexandra Mannings of the University of California, Santa Cruz, said in a statement. "Most of the galaxies are massive, relatively young, and still forming stars. The imaging allows us to get a better idea of the overall host-galaxy properties, such as its mass and star-formation rate, as well as probe what's happening right at the FRB position because Hubble has such great resolution."

FRBs are divided into two broad classes, the repeating ones and the non-repeating ones. Among the FRBs in this study is FRB 180924, among the first non-repeating FRBs to be tracked down to its galaxy of origin.

The region of origin of four FRBs in this study. FRB 190714 (top left), FRB 191001 (top right), FRB 180924 (bottom left), and FRB 190608 (bottom right). Credits: SCIENCE: NASA, ESA, Alexandra Mannings (UC Santa Cruz), Wen-fai Fong (Northwestern) IMAGE PROCESSING: Alyssa Pagan (STScI)

The exact mechanism that powers these blink-and-you’ll-miss-it bursts of radio waves is still unclear but this study gives credence to the leading hypothesis that the source is flares from magnetars. Magnetars are special types of neutron stars, the collapsed cores left over by certain supernovae, with an incredible magnetic field.

When such stars flare up they release brief but powerful emissions and if the alignment is right we can catch such emissions from Earth. Finding the origin of these emissions in star-forming massive galaxies strengthens this idea as they are likely to have a larger population of magnetars.

"Owing to their strong magnetic fields, magnetars are quite unpredictable," said co-author Wen-fai Fong of Northwestern University. "In this case, the FRBs are thought to come from flares from a young magnetar. Massive stars go through stellar evolution and become neutron stars, some of which can be strongly magnetized, leading to flares and magnetic processes on their surfaces, which can emit radio light. Our study fits in with that picture and rules out either very young or very old progenitors for FRBs."

It's impressive how far the field of FRBs has come in such a short amount of time, since the first discovery in 2001. "This is such a new and exciting field," Fong added. "Finding these localized events is a major piece to the puzzle, and a very unique puzzle piece compared to what's been done before. This is a unique contribution of Hubble."


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