Less than a year after launching, NASA’s Imaging X-ray Polarimetry Explorer’s(IXPE)
observations of a neutron star have led to confirmation of what
scientists have only previously theorized: magnetars have ultra-strong
magnetic fields and are highly polarized.
Scientists used IXPE to observe the magnetar 4U 0142+61, a neutron
star located in the Cassiopeia constellation, about 13,000 light-years
away from Earth. This is the first-ever observation X-ray polarization
from a magnetar, a neutron star with the most powerful magnetic fields
in the universe.
Astronomers found that the neutron star likely has a solid surface
and no atmosphere. This is the first time that scientists have been able
to reliably conclude that a neutron star has a bare solid crust, a
finding enabled by IXPE’s X-ray polarization measurements.
Polarization is a property of light that tells us about the
interconnected electric and magnetic fields that make up all wavelengths
of light. These fields oscillate, or vibrate, at right angles relative
to the light’s path of travel. When its electric fields vibrate in a
single, unified direction, we say the light is polarized.
Astronomers also found that polarization angle depends on the energy
of particles of light, with high energy light at a polarization angle of
90 degrees compared to low energy light.
“We found that the angle of polarization swings by exactly 90
degrees, following what theoretical models would predict if the star had
a solid crust surrounded by an external magnetosphere filled with
electric currents,” said Roberto Taverna of the University of Padova,
lead author of the new study in the journal Science.
Scientists were surprised to learn energy levels can affect polarization.
“Based on current theories for the magnetars, we expected to detect polarization, but no one predicted polarization would depend on energy, as we are seeing in this magnetar,” said Martin Weisskopf, a NASA emeritus scientist who led the IXPE team from the mission’s inception until spring 2022.
This
photo shows the position of magnetar 4U 0142+61 in the universe. The
magnetar is a neutron star located in the Cassiopeia constellation,
about 13,000 light-years away from Earth. Credits: Roberto Taverna
Additionally, the polarization at low energies indicates that the
magnetic field is so unimaginably powerful that it could have turned the
atmosphere around the neutron star into a solid or a liquid.
“This is a phenomenon known as magnetic condensation,” said chairman
of the IXPE’s magnetar topical working group, Roberto Turolla, with the
University of Padova and University College London.
It is still a subject of debate whether magnetars and other neutron stars have atmospheres.
Thanks to X-ray polarization measurements, astrophysicists are now able to check for the degree of polarization and its position angle when testing the parameters of X-ray emission models. The findings from IXPE’s observations will help X-ray astronomers to better understand the physics of extreme objects like magnetars and black holes.
“Beyond the magnetar 4U 0142+61, IXPE is being used to study a wide
range of extreme X-ray sources, and lots of exciting results are coming
in,” said Fabio Muleri, IXPE Italian Project Scientist from the
INAF-Institute for Space Astrophysics and Planetology in Rome.
For Weisskopf, it’s clear that IXPE’s observations have been critical.
“In my mind, there can be no question that IXPE has shown that X-ray
polarimetry is important and relevant to furthering our understanding of
how these fascinating X-ray systems work,” he said. “Future missions
will have to be cognizant of this fact.”
IXPE builds on the discoveries of NASA’s Chandra X-ray Observatory and other space telescopes by measuring the polarization of X-ray light.
Part of NASA’s Small Explorer mission series, IXPE launched on a Falcon 9 rocket from NASA’s Kennedy Space Center in Florida in December 2021. It now orbits 370 miles, or roughly 595 kilometers, above Earth’s equator. The mission is a partnership between NASA and the Italian Space Agency, with partners and science collaborators in 13 countries. Ball Aerospace, headquartered in Broomfield, Colorado, manages spacecraft operations.
By Hannah Maginot, NASA’S Marshall Space Flight CenterMolly Porter
NASA’s Marshall Space Flight Center, Huntsville, Alabama
256-424-5158
molly.a.porter@nasa.gov
Elizabeth Landau
NASA Headquarters, Washington
elandau@nasa.gov
202-358-0845
