For the first time, astronomers have linked mysterious pulses of energy called fast radio bursts (FRBs) to ripples in spacetime emitted by collapsing and colliding stars. The results, published on March 27 in the journal natural astronomy (opens in a new tab)offer a new explanation for FRBs, which have vexed scientists for more than a decade.
FRBs are massive bursts of radio energy that can eclipse all the stars in an entire galaxy combined, while lasting only fractions of a second. Although FRBs were discovered in 2007, their origins remain shrouded in mystery. This is partly because, while some FRBs repeat periodically, many appear and disappear within milliseconds.
Magnetars – the ultra-dense, collapsed cores of exploded stars (known as neutron stars) with strong magnetic fields — are the main candidates for FRB issuance. But recent observations suggest there may be several possible sources, which may include neutron star collisions.
In April 2019, the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected ripples in spacetime known as gravitational waves of a neutron star merger designated GW190425. A few hours later, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) spotted a bright, non-repeating FRB from the same region of space.
“We found that a burst of radio waves, lasting one thousandth of a second, was generated two and a half hours after the merger of two neutron stars, which are the extremely dense remnants of massive stars. exploded”, co-author of the study Clancy James (opens in a new tab), a radio astronomer from Curtin University in Australia, told Live Science via email. “Our theory is that this burst of radio waves occurred because the merger created a ‘supermassive’ neutron star which, when its rotation slowed, collapsed into a black hole.”
While neutron star mergers have been suggested as possible causes of FRBs in the past, the new observations provide the first evidence that the theory may be correct. The team used three main pieces of information to make this link.
“First, the timing of events,” James said; the FRB arrived only 2.5 hours after the gravitational wave signal. Second, the location of the FRB was consistent with that of the gravitational wave.
“And third, distance,” added James. “It was mainly the distance that helped.”
While most FRBs arrive from billions of light years away, gravitational wave detectors such as LIGO are only sensitive to distances of about 500 million light-years. This FRB was unusually close, and its estimated distance matched that estimated from GW190425.
“What surprised us was how well all the pieces fell into place!” said James. “It was a nice clean pulse – exactly what you would expect from a cataclysmic event.”
According to James, these results indicate that there are at least two different families of FRBs: single FRBs from cataclysmic events such as neutron star mergers, and repetition of FRBs produced by magnetars or some other unknown source.
This discovery may also affect scientists’ understanding of neutron stars, as it suggests that the largest possible mass of these stellar remnants could be greater than currently predicted.
“That’s because the object resulting from the merger of two neutron stars didn’t immediately collapse into a black hole, but could temporarily resist gravity,” James said. “In turn, this tells us something about the fundamental nature of matter at extreme densities and pressures, which we cannot study here on Earth. It could even be evidence for a new type of star – a quark star.”
The team hopes to strengthen the relationship between FRBs and neutron star mergers as gravitational wave observatories around the world begin new observations this spring.
“The next operation of gravitational wave observatories, O4, begins in May and CHIME and other radio telescopes like the Murchison Widefield Array I work with are waiting to see if there is an FRB of all star mergers at neutrons that are seen,” James said. “We are also ordering a new instrument to detect more FRBs and locate them in their galaxies. Hopefully this will start working soon!