Massive ‘Kilonova’ Explosion Shows First Observed Birth of a Magnetar

Magnetars are some of the most extreme objects in the universe, and that’s saying something. These stellar remnants are neutron stars, but whereas most neutron stars are quiet and keep to themselves, magnetars have magnetic fields billions of times more powerful than Earth’s, and they may be the source of the mysterious Fast Radio Bursts astronomers have been tracking in recent years. We’ve never seen a magnetar come into being, but a new high-energy event several billion light-years away might be the first — a kilonova that signals the merging of two neutron stars.

Neutron stars, white dwarfs, and black holes are all stellar remnants that we hear about on a regular basis. The fate of a main-sequence star to become one of these objects is primarily a function of its mass. The largest stars become black holes, while slightly smaller ones become neutron stars. A star like the sun will eventually collapse into a white dwarf. A neutron star can also end up as a pulsar or magnetar, depending on its properties. Other neutron stars can merge with each other to become magnetars, and that’s what astronomers think they’ve spotted.

Scientists believe magnetars produce their ultra-strong magnetic field thanks to superconducting material sloshing around inside. The effects of magnetic fields this powerful are almost unfathomable, so naturally, the formation of such an object is a highly energetic event. The leading theories claim magnetars can come into being when two small-ish neutron stars collide. If they’re too large, the resulting object is a black hole, but with just the right mass, you end up with a magnetar.

Last May, astronomers detected a gamma-ray beacon from an object over 5.5 billion light years away. This matched the theoretical signature of a magnetar formation, so teams around the world turned their most powerful instruments toward the source, including NASA’s Swift Observatory in space, the Very Large Array in New Mexico, and the Keck Observatory in Hawaii. The best data came from none other than the always-reliable Hubble Space Telescope.

Hubble successfully detected the infrared emission (see above) from the formation of heavy elements like gold, platinum, and uranium. That’s another thing astronomers expect to see in a neutron star collision, sometimes known as a kilonova. The team notes that the IR signal was much brighter than anyone expected — 10 times brighter, in fact. For some, this could be confirmation of magnetar formation. If the neutron stars had formed a black hole, the IR emission would have been within expected ranges.

This research still needs to be vetted by other teams, but it’s available on the preprint arXiv.org server. If confirmed, this would be the first time we’ve seen a magnetar born, and the massive energy output recorded by Hubble could reveal a great deal about how these bizarre objects work.

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