A team of astronomers using the Chinese Insight-HXMT x-ray telescope have made a direct measurement of the strongest magnetic field in the known universe. The magnetic field belongs to a magnetar currently in the process of cannibalizing an orbiting companion.
Magnetars are nasty, but thankfully rare. They are a special kind of neutron star that power up the strongest known magnetic fields.
Astronomers don’t know the exact origins of these ultra-powerful fields, but as usual they have their suspicions. While neutron stars are made of almost entirely neutrons, they do contain small populations of protons and electrons. When neutron stars are born in supernova explosions of a massive star, those charged particles can briefly create a strong magnetic field. In normal neutron stars, the magnetic field quickly melts away from all the complex physics happening in the explosion. But for some neutron stars, the magnetic field locks itself in before that happens. When the neutron star finally reveals itself, it retains this impressive magnetic strength, and a magnetar is born.
But most of the time astronomers have to make due with indirect measurements of magnetar magnetic field strengths. Thankfully, sometimes astronomers can get lucky.
Recently a team of astronomers used the new Chinese Insight-HXMT observatory to study J0243.6+6124, an ultraliminous pulsar in the Milky Way. This pulsar has an orbiting companion that wandered too close. The pulsar’s extreme gravity is currently in the process of tearing apart the companion, forcing its material into a thin accretion disk around the pulsar.
Occasionally the gas in the accretion disk flares, producing a flash of incredibly bright x-rays. In the spectrum of those x-rays the astronomers found an absorption line caused by electrons knocking away x-rays. Those electrons can only get that kind of energy if they’re powered by a magnetic field, and so through that observation the astronomers were able to directly measure the magnetic field strengths.
They estimated a field strength of 1.6 billion tesla, which is about a million billion times stronger than the Earth’s magnetic field.