A mysterious radio signal from 30,000 light years away might have come from a ‘volcano’ on a dead star, and could throw light on a bigger mystery - fast radio bursts.
Fast radio bursts are bright pulses of radio emission mere milliseconds in duration, thought to originate from distant galaxies.
Scientists believe the signals come from collapsed stars - but some have suggested they might be evidence of extraterrestrial civilisations.
Matthew Baring, of Rice University, analysed a mysterious signal from a dead neutron star, where on 5 October 2020, the rapidly rotating corpse of a long-dead star about 30,000 light years from Earth changed speeds.
First, its spinning slowed, and a few days later, it abruptly started emitting radio waves.
Analysing data from telescopes on Earth, they showed the sudden slowdown (or ‘anti-glitch’) could have been caused by a volcano-like rupture on the surface of the star that spewed a “wind” of massive particles into space.
Professor Baring said, “People have speculated that neutron stars could have the equivalent of volcanoes on their surface. Our findings suggest that could be the case and that on this occasion, the rupture was most likely at or near the star’s magnetic pole.”
SGR 1935+2154 and other magnetars are a type of neutron star, the compact remains of a dead star that collapsed under intense gravity.
About a dozen miles wide and as dense as the nucleus of an atom, magnetars rotate once every few seconds and feature the most intense magnetic fields in the universe.
“What makes the October 2020 event unique is that there was a fast radio burst from the magnetar just a few days after the anti-glitch, as well as a switch-on of pulsed, ephemeral radio emission shortly thereafter,” he said.
“We’ve seen only a handful of transient pulsed radio magnetars, and this is the first time we’ve seen a radio switch-on of a magnetar almost contemporaneous with an anti-glitch.”
Baring argued this timing coincidence suggests the anti-glitch and radio emissions were caused by the same event, and he’s hopeful that additional studies of the volcanism model will provide more answers.
“The wind interpretation provides a path to understanding why the radio emission switches on,” he said. “It provides new insight we have not had before.”
Abrupt rotational slowdowns of magnetars are very rare.
Astronomers have only recorded three of the “anti-glitches,” including the October 2020 event.
Baring said the model uses only standard physics, specifically changes in angular momentum and conservation of energy, to account for the rotational slowdown.
“A strong, massive particle wind emanating from the star for a few hours could establish the conditions for the drop in rotational period,” he said. “Our calculations showed such a wind would also have the power to change the geometry of the magnetic field outside the neutron star.”
The rupture could be a volcano-like formation, because “the general properties of the X-ray pulsation likely require the wind to be launched from a localised region on the surface,” he said.
Watch: Astronomers at MIT pick up mysterious signal