Scientists have uncovered a “universal law” that applies to certain extreme, ultra-dense stars, and the research could help to shed light on mysterious flashes known as fast radio bursts (FRBs) that are among the most perplexing phenomena in the universe.
An international team of researchers led by Michael Kramer and Kuo Liu from the Max Planck Institute for Radio Astronomy in Bonn, Germany, investigated a rare class of stars known as magnetars—a type of neutron star—for a study published in the journal Nature Astronomy.
Neutron stars are dense objects that have roughly similar masses to the sun while being only about the size of a small city. These spheres, which are the collapsed cores of massive stars, have extremely strong magnetic fields. They are considered to be among the densest objects in the universe, second only to black holes.
Research interest in the properties of magnetars has grown in recent years given their potential link to FRBs—millisecond-long bursts, or flashes, of radio waves that originate from distant sources in the universe.
Michael Kramer/MPIfR
The origin of these radio bursts remains a mystery, but some scientists have speculated that magnetars may be one of the potential sources of at least some FRBs. It is this potential link between magnetars and FRBs that the international team of researchers wanted to explore in the Nature Astronomy study.
The study uncovered an underlying physical law that appears to apply universally to a range of objects known as neutron stars, including pulsars and magnetars. The law provides insights into how these stars produce radio emissions and could potentially help scientists to understand the nature of FRBs, Kramer told Newsweek.
“Detecting FRBs is in principle not too difficult, but what they are, is a complete mystery,” he said. “Magnetars are by themselves very interesting objects, but the possibility that they may be behind the phenomenon of fast radio bursts makes them even more intriguing.”
Most of the roughly 3,000 known neutron stars are classified as “pulsars.” These objects rotate rapidly and shoot out twin beams of radiation from their magnetic poles. These beams, which consist of radio wave emissions, sweep across the sky like those from a lighthouse. The beams are visible as a pulsating signal when rotating pulsars shine them toward our telescopes.
Magnetars, on the other hand, are much rarer, with only around 30 having been discovered. Magnetars are neutron stars with particularly strong magnetic fields—roughly a trillion times stronger than Earth’s.
They rotate more slowly compared to normal neutron stars and typically emit radiation in high-energy X-rays, rather than lower-energy radio waves. But to date, a small handful of the known magnetars—about six or seven—have also been observed spewing out beams of radio emissions in a similar manner to pulsars, at least on occasion.
In the latest study, Kramer and colleagues used radio telescopes to examine in detail individual pulses of the few magnetars known to emit at radio frequencies, as well as the structure of the pulses. They then compared their results to what had been found in the past for pulsars and other types of rotating neutron stars.
The team already knew that there are some similarities in the structure of the pulses of magnetars that produce radio emissions and the bursts of “extragalactic” (meaning outside our galaxy) FRBs.
“This reminded us about normal pulsars, where something similar had been seen. So, we thought that if magnetars are indeed related to FRBs, we should find a similar structure also in magnetar emissions. That is why we studied the radio emission of the magnetars known to emit at radio frequencies,” Kramer said.
“We thought that if they show the same or similar structure, it could support the interpretation of FRBs as the emission of extragalactic magnetars. And, indeed, they do.”
The team found that a similar pulse structure was also seen in pulsars and other types of neutron stars that emit radio emissions. The findings enabled the researchers to conclude that there is a universal relationship linking the structure of radio wave pulses produced by neutron stars with their rotational period—meaning the time it takes for the object to complete a full rotation.
This relationship could then be used in future to interpret FRBs as the emissions of magnetars, which would solve an important astrophysical mystery, the researchers said.
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Newsweek is committed to challenging conventional wisdom and finding connections in the search for common ground.