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Study uncovers universal law governing neutron star radio emission

An international research team, spearheaded by Michael Kramer and Kuo Liu at the Max Planck Institute for Radio Astronomy in Bonn, Germany, has delved into the intricate realm of magnetars, uncovering a universal law that appears to govern stars. These findings offer valuable insights into the mechanisms behind radio emission from these celestial sources and potentially provide a crucial link to the mysterious phenomena of fast radio bursts (FRBs) originating from the distant cosmos. The comprehensive study led by the researchers is now published in Nature Astronomy.

Neutron stars, the remnants of massive stellar cores, boast an extraordinary density, concentrating up to twice the mass of the sun within a sphere of less than 25 km in diameter. This immense density squeezes electrons and protons into neutrons, giving rise to the name “neutron stars.” Over 3,000 neutron stars are observable as radio pulsars, emitting a visible pulsating signal when a radio beam is directed toward Earth during their rotation.

Pulsars already possess magnetic fields a thousand billion times stronger than Earth's, but a subset of neutron stars, known as magnetars, takes this to another level with magnetic fields even stronger, surpassing those of regular pulsars by a factor of 1,000. Among the roughly 30 known magnetars, six intermittently emit radio signals. There is a hypothesis that extragalactic magnetars might be the source of fast radio bursts (FRBs).

To explore this potential link, researchers from the Max Planck Institute for Radio Astronomy (MPIfR), in collaboration with colleagues from the University of Manchester, conducted a detailed analysis of individual pulses from magnetars. They discovered sub-structures in these pulses, reminiscent of those observed in pulsars, particularly the fast-rotating millisecond pulsars, and in other sources known as Rotating Radio Transients.

What surprised the researchers was the revelation that the timescales of magnetars and other types of neutron stars followed the same universal relationship, precisely scaling with the rotation period. Whether a neutron star rotates in a few milliseconds or nearly 100 seconds, the behavior appears consistent with that of magnetars, suggesting a shared intrinsic origin for the subpulse structure in all radio-loud neutron stars.

This insight provides valuable information about the plasma processes responsible for radio emission, offering a potential key to interpreting similar structures observed in FRBs. Michael Kramer, the first author of the paper and Director at MPIfR, noted, “When we set out to compare magnetar emission with that of FRBs, we expected similarities. What we didn't expect is that all radio-loud neutron stars share this universal scaling.”

Kuo Liu added, “We expect magnetars to be powered by energy, while the others are powered by their rotational energy. Some are very old, some are very young, and yet all seem to follow this law.”

Gregory Desvignes emphasized the importance of flexibility in their observations, stating, “Since magnetar radio emission is not always present, one needs to be flexible and react quickly, which is possible with telescopes like the one in Effelsberg.” Ramesh Karuppusamy highlighted the role of the 100-m radio telescope in Effelsberg in their observations.

For co-author Ben Stappers, the most exciting aspect of the results is the potential connection to FRBs. “If at least some FRBs originate from magnetars, the timescale of the substructure in the burst might then tell us the rotation period of the underlying magnetar source. If we find this periodicity in the data, this would be a milestone in explaining this type of FRB as radio sources.” Michael Kramer concluded, “With this information, the search is on.”

Source: Max Planck Society

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