The secrets of deep space may be starting to reveal themselves, as rapid advances in technology and stronger research collaborations are making it possible for astronomers to piece together cosmological clues like never before.
In the March 27 issue of the journal Nature Astronomy, an international team of scientists shows for the first time a possible relationship between neutron star mergers and fast radio bursts (FRBs) – two of the most mysterious cosmological phenomena studied over the past two decades.
The team, which includes researchers from UNLV, University of Western Australia (UWA), and Curtin University, reports on the observation of a deep space neutron star merger followed just 2 ½ hours later by an observed FRB. If confirmed, the correlation between the two events could unlock part of the mystery of how FRBs are generated.
Fast radio bursts (FRBs) are millisecond-long pulses of electromagnetic radio waves that occur in deep space and produce the energy equivalent to the sun’s annual output. Most FRBs occur as one-off events, while others present as repeating bursts. Though their origins are still a bit of a mystery, the fraction of FRBs emitted as repeated bursts are likely produced by highly magnetized neutron stars known as magnetars.
Though one-off bursts may share a similar origin, this study suggests that they may also be formed as a result of gravitational waves (GWs) generated by colliding neutron stars.
“An association like this one is not completely unexpected,” said UNLV astrophysicist and study co-author Bing Zhang, who initially proposed a GW-FRB association scenario back in 2014. “One possibility is that the merger of neutron stars leaves behind a rapidly spinning massive neutron star rather than a black hole. The neutron star eventually collapses to a black hole after it spins down, ejecting its magnetosphere to create the FRB.”
Gravitational wave (GW) detectors, including the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the U.S. and the Virgo detector in Italy, have been observing GW events from collisions of black holes or neutron stars since 2015.
Both the GW event and the FRB event in the proposed association were detected on April 25, 2019. The binary neutron star merger event, dubbed GW190425, was the second event of its kind ever detected by GW detectors. The FRB event, dubbed FRB 20190425A, was detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and occurred about 2 ½ hours later.
As the connection between neutron star mergers and FRBs had long been theorized but not observed, researchers from UWA (grad student Alexandra Moroianu and professor Linqing Wen) and Curtin University (professor Clancy James) blindly searched for possible GW-FRB associations. They eventually identified this pair, which occurred in a similar area of space and suggest a probability that they’re possibly linked.
“This is extremely exciting and would certainly help unravel some of the mystery surrounding these fast radio bursts, such as why repeating and non-repeating bursts exhibit different properties,” said study lead author Alexandra Moroianu, who overcame serious health complications during the course of her research.
Though even the possibility that the two are linked is encouraging to astronomers, Zhang, who along with UNLV doctoral student Shunke Ai presented the theoretical modeling to interpret the event, cautions that further observations are needed to strengthen the correlation.
“Given the chance probability statistics, I wouldn’t definitively confirm the association just yet”, said Zhang. “At the same time, though, the potential association presented in this work definitely calls for closer scrutiny of future GW–FRB associations.”
Zhang says that with another observing run of gravitational wave detectors just around the corner and with more FRB detection machines in place, more data will be accumulated to eventually test whether such associations are physical and common.
“If this is the case, then the nuclear matter must be very ‘stiff’ at very high densities, which means that a neutron star can sustain a lot of mass,” said Zhang. “The maximum mass of neutron stars would be much larger than currently most people believe.”
The study, “An assessment of the association between a fast radio burst and binary neutron star merger”, appeared March 27 in the journal Nature Astronomy and includes seven co-authors from the three institutions: University of Western Australia, Curtin University, and UNLV.