Australian scientists have measured strange signals 4,000 light years away. It could be a new class of neutron stars.
About 38 quadrillion kilometres from Earth, 4,000 light years away, an unknown celestial object from our galaxy regularly emits electromagnetic waves. It's pulsating. But what is it?
Scientists from Australia were confronted with this question in 2018. At the time, a student detected signals that were repeated every 18 minutes. The energy waves were measured for three months. Then they disappeared again.
Galactic beacon
The explanation, which the team published in the scientific journal Nature, is as follows: The unknown object may be a new class of slowly rotating, very bright neutron stars with an extremely strong magnetic field. The object's radio wave signal, which can simplistically be thought of as a galactic beacon, lasts 30 to 60 seconds at a time. A comparable pulse frequency has not yet been observed.
The fact that the signals have disappeared again suggests that they are related to a dramatic, one-off event, possibly a star quake. It was scary for an astronomer because there is nothing in the sky to do this," says Natasha Hurley-Walker of the International Centre for Radio Astronomy Research at Curtin University in Australia. Hurley-Walker leads the team that made the discovery.
The researchers said they quickly dismissed the idea that the unusual object was a sign of extraterrestrial life, a technologically advanced civilisation. This was because the team discovered that the signal - one of the brightest radio sources in the sky - could be detected across a wide frequency spectrum. It would have required a huge amount of energy to generate it. "It's definitely not aliens," said Hurley-Walker.
Another argument against the alien thesis is that the existence of such an object - an "ultra-long-period magnetar" - can be explained astronomically. It's just that no one expected to detect such a star directly, Hurley-Walker said, "because we didn't expect them to be so bright".
The signal usually gets weaker when the neutron star loses energy
A neutron star is what astronomers call the dark, dense remnant that remains after a supermassive star collapses after a supernova. Shrunk to the size of a small city, such a neutron star initially spins very fast. It flashes up and down for milliseconds or seconds. Over time, the neutron star loses energy and slows down. And in fact, its signal should become weaker.
Why the newly detected object - if it is a magnetar - is still emitting enough energy to be detectable is not yet clear. "Somehow it converts magnetic energy into radio waves much more efficiently than anything we've seen before," says Hurley-Walker.
Scientists now hope to gain more clarity about the mysterious celestial object and its origins through further observations.
