New record for measuring the strongest magnetic field in the universe

(ORDO NEWS) — Neutron stars have the strongest magnetic fields in the universe, and the only way to directly measure their surface magnetic field is to observe cyclotron absorption lines in their X-ray energy spectra.

The Insight-HXMT team recently detected a 146 keV cyclotron absorption line in the X-ray spectrum of the neutron star Swift J0243.6+6124, which corresponds to a surface magnetic field of over 1.6 billion Tesla.

After directly measuring the strongest magnetic field in the universe at around 1 billion Tesla, world records for the highest energy cyclotron absorption line and direct measurement of the strongest magnetic field in the universe will be broken in 2020.

Numerous observations have shown that the X-ray spectra of objects of this type contain absorption structures, namely cyclotron absorption lines, which are believed to be caused by resonant scattering and hence the absorption of X-rays by electrons moving along strong magnetic fields.

The energy of the absorption structure corresponds to the strength of the surface magnetic field of the neutron star, so this phenomenon can be used to directly measure the strength of the magnetic field near the surface of the neutron star.

Insight-HXMT has made detailed and broadband observations of Swift J0243.6+6124, the Milky Way’s first superluminal X-ray pulsar, and has unequivocally detected its cyclotron absorption line.

This line detected energies up to 146 keV (with a detection significance of about 10 times the standard deviation), which corresponds to a surface magnetic field of over 1.6 billion Tesla.

This is not only the strongest magnetic field directly measured in the universe to date, but also the first detection of an electron cyclotron absorption line in a superluminous X-ray source, providing a direct measurement of the surface magnetic field of a neutron star.

It is believed that the surface magnetic fields of neutron stars have a complex structure: from dipole fields located very far from the neutron star to multipole fields that affect only the region near the neutron star.

However, most of the previous indirect estimates of the magnetic fields of neutron stars have investigated only dipole fields.

This time, the direct measurement of the Insight-HXMT magnetic field based on the cyclotron absorption line turned out to be an order of magnitude larger than the estimate by indirect methods.

This provides the first concrete evidence that the structure of the neutron star’s magnetic field is more complex than the traditional symmetric dipole field, and also provides the first measurement of the nonsymmetric component of the neutron star’s magnetic field.

Insight-HXMT is China’s first X-ray astronomy satellite. It includes a scientific payload of a high-energy telescope, a medium-energy telescope, a low-energy telescope, and a space environment monitor.

Insight-HXMT has advantages over other X-ray satellites in terms of broadband (1-250 keV) spectral coverage, large effective area at high energies, high temporal resolution, low dead time, and no clutter effect for bright sources, opening a new window for observing black holes, neutron stars with fast transitions in the hard X-ray range and energy spectrum studies.

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