An international research team led by Michael Kramer and Kuo Liu from the Max Planck Institute for Radio Astronomy in Bonn, Germany, studied magnetars to discover a fundamental law that could be universally applied to neutron stars.

This law provides insight into how these sources generate radio emissions and may provide a link to fast radio bursts, mysterious bursts of radio light originating from deep space. Their research has been published at: Nature Astronomy.

Neutron stars are the collapsed cores of massive stars that pack twice the mass of the Sun into a sphere less than 25 km in diameter. As a result, matter is the most densely packed matter in the observable universe; It compresses electrons and protons into neutrons, hence its name. More than 3,000 neutron stars can be observed as radio pulsars when they emit a radio beam visible from Earth as a pulsating signal as they reflect rotating pulsar light into our telescopes.

The magnetic field of pulsars is currently a thousand billion times stronger than the Earth’s magnetic field, but there is also a small group of neutron stars whose magnetic fields are 1000 times stronger. These are so-called magnetars. Of the 30 or so known magnetars, six emit radio radiation at least occasionally. The source of fast radio bursts (FRBs) is believed to be extragalactic magnetars.

To study this connection, researchers from the Max Planck Institute for Radio Astronomy (MPIfR), with the help of colleagues from the University of Manchester, examined individual magnetar pulses in detail and identified the substructures. It turns out that a similar momentum structure is observed in pulsars, fast-spinning millisecond pulsars, and other neutron star sources known as spinning radio transits.

Surprisingly, the researchers found that the time scale of magnetars and other types of neutron stars follows the same universal relationship and scales exactly with the rotation period. The fact that a neutron star with a rotation period of less than a few milliseconds and a neutron star with a rotation period of about 100 seconds behaves like a magnetar suggests that the internal origin of the subimpact structure must be the same for all radio-high neutron stars.

This reveals information about the plasma process responsible for the radio emission itself and enables the interpretation of similar structures observed in FRBs as a result of the corresponding rotation period.

“When we started comparing magnetar emission with FRB emission, we expected similarities,” says Michael Kramer, first author of the paper and director of MPIfR. “We did not expect all radio-emitting neutron stars to have such universal scaling.”

“We expect magnetars to be powered by magnetic field energy, while others are powered by spin energy,” says Kuo Liu. “Some are very old, some are very young, but they all seem to obey the law.”

“We observed magnetars with the 100-meter radio telescope in Effelsberg and also compared our results with archival data, because magnetars do not always emit radio radiation,” says Gregory Desvin.

“Because magnetic radio emission is not always present, you need to be flexible and react quickly, which is possible with telescopes like the one at Effelsberg,” says Ramesh Karuppusamy.

For study co-author Ben Steppers, the most exciting aspect of the result is the possible connection to FRBs. “If at least some FRBs originate from magnetars, the time scale of substructure in the flare can tell us the spin period of the underlying magnetar source. If we find such periodicity in the data, this would be a breakthrough in elucidating this type of FRB as a radio source.”

“With this information, the search continues,” says Kramer.