Massive stellar deaths are some of the most monumental and explosive events in the universe. Smaller stars like our sun will die a relatively quiet death, puffing up to about the size of Mars’ orbit before gradually cooling off and sloughing gas to form a planetary nebula while its remains condense into a white dwarf. Stars that are several times the mass of our sun tend to go out with more of a bang, and what they leave behind are the beasts of the void.
The Beginning Of The End
In late 2017, astronomers noticed signals indicating a massive collision. Observatories and laboratories across the world and in orbit all registered the event. The detection of the merger across the electromagnetic spectrum and in the form of gravitational waves marked the foundation of multimessenger astronomy, which is based on based on the coordinated observation and interpretation of disparate “messenger” signals (electromagnetic radiation, gravitational waves, neutrinos, and cosmic rays). Turning their eyes to the sky, astronomers expected to find a brand new black hole.
The source of the commotion was the merger of two neutron stars, leftovers from a pair of once-massive stars. The two neutron stars collided and emitted gamma rays, x-rays, a visible light burst, gravitational waves, and more, all of which were detected here on Earth. Audio signals of the collision, when combined with the other evidence, led scientists to believe that a black hole had been formed. Further studies instead revealed one of the most massive magnetars ever observed.
A 100-Million Ton Tablespoon
Magnetars are the most potent magnetic objects in the known universe. Their pull is so strong that life cannot exist within 1000 km of a magnetar’s surface. At that distance, the gravitational field of the star tears apart atoms, stretching them out into impossibly-thin cylinders. The material that makes up these stars is 10,000 times denser than lead, and a tablespoon full of it would weigh over 100 million tons. To match the strength of a magnetar’s magnetic field, you’d have to multiply Earth’s magnetic field by ten 16 times.
Since their discovery in 1979, fewer than 30 magnetars have been measured and confirmed. The one that produced the gravitational wave GW170817 back in 2017 is the most recently discovered. When scientists listened to the sound waves generated by the merger, they heard an ascending tone, followed by a five-second descending tone that indicated the birth of a magnetar. The latter half of the sound pattern was the main identifying factor for the new star.
The Fate Of A Giant
The hypermassive magnetar born of the merger event currently (from our perspective) spins happily, whirring about at a dizzying rate. Had it gone on to become a hypermassive neutron star, it might have slowed its spin to live a long life, but as a magnetar, this star’s remaining life is as likely to be short as it is to be unpredictable.
Most magnetars only live for about 10,000 years before their magnetic fields decay, and their explosive gamma-ray bursts cease, rendering the star “inactive.” In the case of this particular giant, scientists aren’t sure if it will live a short, brilliant life as a fast-spinning pulsar or if it will eventually collapse into a black hole. However the star lives out its final years, its formation was a cornerstone event for astronomers across the globe.