Distant Magnetar Has Solid Surface with No Atmosphere

by johnsmith

Magnetars are neutron stars with ultra-strong magnetic fields, which can be observed in X-rays. Polarization measurements could provide information on their magnetic fields and surface properties. Now, astronomers using the NASA/ASI Imaging X-ray Polarimetry Explorer (IXPE) have observed polarized X-rays from a Galactic magnetar called 4U 0142+61 (PSR J0146+6145).

An artist’s impression of a magnetar. Image credit: NASA’s Goddard Space Flight Center / S. Wiessinger.

An artist’s impression of a magnetar. Image credit: NASA’s Goddard Space Flight Center / S. Wiessinger.

Magnetars are neutron stars with magnetic fields that are about a quadrillion times greater than the magnetic field of Earth.

These huge magnetic fields are thought to be produced when an rapidly rotating neutron star is formed by the collapse of the core of a massive star.

Magnetars emit bright X-rays and show erratic periods of activity, with the emission of bursts and flares which can release in just one second an amount of energy millions of times greater than our Sun emits in one year.

Using the IXPE observatory, University of Padova astrophysicist Roberto Taverna and colleagues detected polarized X-rays from 4U 0142+61, a magnetar located some 13,000 light-years away in the constellation of Cassiopeia.

They found a much lower proportion of polarised light than would be expected if the X-rays passed through an atmosphere.

They also found that, for particles of light at higher energies, the angle of polarisation flipped by exactly 90 degrees compared to light at lower energies, following what theoretical models would predict if the star had a solid crust surrounded by an external magnetosphere filled with electric currents.

“This was completely unexpected. I was convinced there would be an atmosphere,” said University College London’s Professor Silvia Zane.

“The star’s gas has reached a tipping point and become solid in a similar way that water might turn to ice. This is a result of the star’s incredibly strong magnetic field.”

“But, like with water, temperature is also a factor — a hotter gas will require a stronger magnetic field to become solid.”

“The most exciting feature we could observe is the change in polarisation direction with energy, with the polarisation angle swinging by exactly 90 degrees,” Dr. Taverna said.

“This is in agreement with what theoretical models predict and confirms that magnetars are indeed endowed with ultra-strong magnetic fields.”

“The polarisation at low energies is telling us that the magnetic field is likely so strong to turn the atmosphere around the star into a solid or a liquid, a phenomenon known as magnetic condensation,” said University of Padova’s Professor Roberto Turolla.

“The solid crust of the star is thought to be composed of a lattice of ions, held together by the magnetic field. The atoms would not be spherical, but elongated in the direction of the magnetic field.”

“It is still a subject of debate whether or not magnetars and other neutron stars have atmospheres.”

“However, the new paper is the first observation of a neutron star where a solid crust is a reliable explanation.”

“It is also worth noting that including quantum electrodynamics effects, as we did in our theoretical modeling, gives results compatible with the IXPE observation,” said University of British Columbia’s Professor Jeremy Heyl.

“Nevertheless, we are also investigating alternative models to explain the IXPE data, for which proper numerical simulations are still lacking.”

The findings appear in the journal Science.


Roberto Taverna et al. Polarized X-rays from a magnetar. Science, published online November 3, 2022; doi: 10.1126/science.add0080

Source link: https://www.sci.news/astronomy/magnetar-solid-surface-11363.html

Related Posts

Leave a Comment

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More