You can’t see it, but billions of light years away cosmic flash bulbs are popping and no one knows why.
Fast radio bursts, brilliant and intense flashes of energy that blaze for a millisecond and then disappear, have puzzled scientists for years, but West Virginia University astronomers are helping to find the celestial bread crumbs that will help lead scientists to answers about this mysterious phenomenon.
Sarah Burke-Spolaor, assistant professor in the physics and astronomy department of the Eberly College of Arts and Sciences, and Maura McLaughlin, Eberly Distinguished Professor of Physics and Astronomy, are leading members of a team that has pinpointed the location in the sky of one of these bursts for the first time, allowing scientists to determine the distance and home galaxy of one of these pulses of radio waves.
The new findings are featured as the cover story in the Jan. 5, 2017 issue of the scientific journal Nature as well as in companion papers in Astrophysical Journal Letters. A team of astronomers, including Burke-Spolaor, who is co-author on the paper, also presented the findings at the Astronomical Society’s meeting this week in Grapevine, Texas.
Using the National Science Foundation’s Karl G. Jansky Very Large Array, a multi-antenna radio telescope that has the ability to see fine details, scientists now know that the burst came from a dwarf galaxy more than 3 billion light years from Earth. Burke-Spolaor developed the real-time fast radio burst detector at the Very Large Array as a postdoctoral Jansky Fellow.
“For the first time, we have seen how truly remote and bright these bursts are. When they flash, just for an instant they far outshine their whole host galaxy,” Burke-Spolaor said. “In fact, the host galaxy was so faint that we needed both excellent burst localization and deep-sky optical imaging to pin the burst to its host.”
A needle in a haystack
Fast radio bursts are short-lived (millisecond) bursts of radio waves that pack a phenomenally energetic punch. The intense explosions of energy have been seen from many directions on the sky and come from great distances.
The first burst was discovered in 2007 by WVU physics and astronomy professor Duncan Lorimer, his then-undergraduate student David Narkevic, and McLaughlin while scouring archived data from Australia’s Parkes Radio Telescope.
Since then, fewer than two dozen bursts have been documented, but scientists still believe that these bursts occur by the thousands each day.
“In addition to being hard to find due to their short durations, fast radio bursts have so far been very hard to localize with single radio dishes which has made it very hard to say conclusively where they are coming from,” Lorimer said.
The ephemeral nature of these events has made it challenging for scientists to detect them or pin down how and where they were formed. Theories have ranged from a star exploding in a supernova to the far-fetched alien communication.
But recently, astronomers have come closer to discovering the mysterious origins.
A rare occurrence, again
In 2015, an international collaboration of scientists, including McLaughlin, made a valuable discovery that would allow scientists to observe the bursts more closely.
Fast radio bursts were generally thought to be single events that revealed few clues about their locations and sources, but in 2015 an international collaboration of scientists examined data from the Arecibo Radio Telescope in Puerto Rico that showed repeating bursts attributed to one specific fast radio burst.
“We have detected dozens of radio bursts with Arecibo, the Green Bank Telescope in West Virginia, and now the Very Large Array and the Effelsberg Telescope in Germany,” McLaughlin said.
“This is the only known fast radio burst from which repeated bursts have been detected, and it is not yet clear whether this object is representative of the broader population. If it is, however, the localization is a huge step forward in pinpointing their astrophysical origins.”
A far-off place
The repeating bursts from this object, named FRB 121102, allowed astronomers to watch for it using the Very Large Array.
In 83 hours of observing time over six months in 2016, the array detected nine bursts from FRB 121102.
“The Very Large Array data allowed us to narrow down the position very accurately,” Burke-Spolaor said.
With the precise array position, researchers were able to then use 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 3 billion light years from Earth.
In addition to detecting the bright bursts from FRB 121102, the array observations also revealed an ongoing, persistent source of weaker radio emission in the same region.
Next, a team of observers used the multiple radio telescopes of the European VLBI Network, along with the 1,000-foot-diameter William E. Gordon Telescope of the Arecibo Observatory, and the NSF’s Very Long Baseline Array to determine the object’s position with even greater accuracy.
Using these highly sensitive, ultra-high precision instruments, scientists were able to determine that the source must be within 100 light years of each other, and the bursts and source are likely to be either the same object or physically associated with each other.
The top candidates, the astronomers suggested, are a neutron star – possibly a highly-magnetic one – surrounded by either material ejected by a supernova explosion or material ejected by a resulting pulsar, or an active nucleus in the galaxy with radio emission coming from jets of material emitted from the region surrounding a supermassive black hole.
Scientists believe that the bursts and the source are likely to be either the same object or somehow physically associated with each other.
“We are now searching for repeated bursts from other fast radio burst positions, including the original one discovered by our WVU team in 2007,” McLaughlin said. “With luck, more repeaters will be found and more localizations made.”
Fast radio bursts show great promise to understanding how matter is distributed in the universe.
“It’s not often we find a phenomenon so well-tuned to probing the universe,” Burke-Spolaor said. “Identifying more burst hosts will allow us to uniquely explore the host galaxies themselves, the space between galaxies, and other material that fast radio bursts travel through on their path to our telescopes.”
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