Mysterious radio signal traced to distant dwarf galaxy
In a first, astronomers, including one of Indian–origin, have traced the source of a mysterious radio signal to a dwarf galaxy more than three billion light years from Earth. The ‘sporadically repeating milliseconds–long signal’ is one of the rare and brief bursts of cosmic radio waves that have puzzled astronomers since they were first detected nearly a decade ago.
The new information rules out several suggested explanations for the source of Fast Radio Bursts (FRBs) including one that suggested the signal could be coming from within or near our own Milky Way galaxy.
“We now know that this particular burst comes from a dwarf galaxy more than three billion light–years from Earth,” said lead author Shami Chatterjee of Cornell University. “That simple fact is a huge advance in our understanding of these events,” Chatterjee, an alumnus of Indian Institute of Technology –Madras, added.
Fast Radio Bursts are highly–energetic, but very short–lived (millisecond) whose origins have remained a mystery since the first one was detected in 2007. That year, researchers scouring archived data from Australia’s Parkes Radio Telescope in search of new pulsars found the first known FRB – one that had burst in 2001.
There now are 18 known FRBs. All were discovered using single–dish radio telescopes that are unable to narrow down the object’s location with enough precision to allow other observatories to identify its host environment or to find it at other wavelengths. Unlike all the others, however, one FRB, discovered in November of 2012 at the Arecibo Observatory in Puerto Rico, has recurred numerous times.
The repeating bursts from this object, named FRB 121102 after the date of the initial burst, allowed astronomers to watch for it using the US National Science Foundation’s (NSF) Karl G. Jansky Very Large Array (VLA), a multi–antenna radio telescope system with the resolving power, or ability to see fine detail, needed to precisely determine the object’s location in the sky.
In 83 hours of observing time over six months in 2016, the VLA detected nine bursts from FRB 121102.
“For a long time, we came up empty, then got a string of bursts that gave us exactly what we needed,” Casey Law of the University of California at Berkeley said. “The VLA data allowed us to narrow down the position very accurately,” Sarah Burke–Spolaor, of the National Radio Astronomy Observatory (NRAO) and West Virginia University, pointed out.
Using the precise VLA position, researchers used the Gemini North telescope in Hawaii to make a visible–light image that identified a faint dwarf galaxy at the location of the bursts. The Gemini observations also determined that the dwarf galaxy is more than three billion light–years from Earth, according to the study published in the journal Nature.
“Finding the host galaxy of this FRB, and its distance, is a big step forward, but we still have much more to do before we fully understand what these things are,” Chatterjee said.