Discovery of the most powerful magnetic field in the universe

1.6 billion Tesla! This is the strongest surface magnetic field ever recorded in the known universe. This record magnetic field comes from the so-called ultra-bright X-ray magnetar, more precisely from the neutron star Swift J0243.6+6124, which is in the process of cannibalizing another pulsar with which it forms a (deadly) tandem. Thus, it exceeds the previous record, attributed in 2020 to the pulsar GRO J1008-57, by 600 million Tesla and is equivalent to the Earth’s magnetic field by one million billion times.

These results, jointly obtained by the Institute for High Energy Physics (IHEP) of the Chinese Academy of Sciences and the Keplerian Center for Particle Physics and Astrophysics at the University of Tübingen (IAAT), were obtained thanks to the Hard X-ray Modulation Telescope (HXMT) or the Insight-HXMT instrument, a Chinese satellite launched in June 2017 to learn more about neutron stars, black holes, gamma-ray bursts and any other phenomenon that emits X-rays and gamma rays. The researchers’ findings were published June 28, 2022 in the Astrophysical Journal Letters.

Magnetars, rare items

Magnetars are often referred to as “the most powerful magnets in the universe”. It’s more accurate rotating neutron stars, drawing energy from extremely powerful magnetic fields, the strongest in the universe. They are much rarer than pulsars (another type of neutron star) and there are only a handful of them in our galaxy.

When neutron stars are born in a supernova explosion of a massive star, these charged particles can briefly create a strong magnetic field. In “classical” neutron stars, the magnetic field disappears quickly due to all the complex physics that comes with the explosion. But in some neutron stars, the magnetic field “locks up” before that happens. From that moment on, the finally discovered neutron star becomes a magnetar.

Traces of the feast as a measuring tool

Our Swift J0243.6+6124 is more than a “simple” magnetar. Not only is it located in our Milky Way, but it actually stands for an X-ray neutron star binary, the most extreme object that consists of a neutron star and a companion star. Under the colossal gravitational force of the neutron star, the gas from the companion star falls onto the neutron star, forming an accretion disk. “Sliding” along the magnetic lines to the surface of the neutron star, the plasma of the accretion disk then ignites, emitting powerful X-rays, which, as the star rotates, are broadcast by periodic pulsed X-ray signals (hence the name “X-ray accretion pulsar” for these objects).

In the spectrum of these X-rays, astronomers have found an absorption line caused by electrons that cancel out the X-rays and can only behave in this way if they are powered by a magnetic field. Therefore, thanks to this observation, they were able to directly measure the strength of the magnetic field.

This absorption line eventually showed energies up to 146 keV, corresponding to a surface magnetic field of over 1.6 billion Tesla. This is not only the strongest directly measured magnetic field in the Universe to date, but also the first detection of an electron cyclotron absorption line in an ultraluminous X-ray source, providing a direct measurement of the surface magnetic field of a neutron star. Listen up, magnetars, there’s a new power record to go.

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