Astronomers using the Imaging X-ray Polarimetry Explorer (IXPE) — a collaboration between NASA and the Italian Space Agency — have observed the Vela pulsar wind nebula (bright white dot in a purple/blue hazy circle), which is powered by a young pulsar and located inside an extended structure called Vela X, which is itself inside the Vela supernova remnant.
This image shows the Vela pulsar wind nebula: light blue represents X-ray polarization data from IXPE; pink and purple colors correspond to data from NASA’s Chandra X-ray observatory; the NASA/ESA Hubble Space Telescope contributed the stars in the background. Image credit: IXPE / NASA / MSFC / Fei Xie / CXC / SAO / STScI / Hubble / Chandra / Judy Schmidt / Kimberly Arcand / Nancy Wolk.
The Vela pulsar is located in the constellation Vela, approximately 1,000 light-years away.
It spins about 11.2 times per second, is about 25 km (15 miles) in diameter, and is known to glitch about once every three years.
In a new study, Guangxi University’s Professor Fei Xie and colleagues were surprised about the high degree of polarization they found in X-rays at the Vela pulsar wind nebula.
“This is the highest degree of polarization measured in a celestial X-ray source to date,” Professor Xie said.
High polarization means that the electromagnetic fields are well organized; they are lined up in specific directions, and depend on their position in the nebula.
What’s more, the X-rays that IXPE detects come from high-energy electrons spiraling in the magnetic fields of the pulsar wind nebula, called synchrotron emission.
Highly polarized X-rays means that these magnetic fields, too, must be well organized.
“In contrast to supernova remnants that have a shell of material around them, the high polarization of the X-rays suggests that the electrons were not accelerated by the turbulent shocks that seem important in other X-ray sources,” said Dr. Roger Romani, an astrophysicist at Stanford University.
“Instead, there must be some other process involved, such as magnetic reconnection, which involves the breaking and joining of magnetic field lines.”
“That is a way in which magnetic energy gets converted to particle energy.”
IXPE data also suggest that the magnetic field is aligned as a smooth donut-shaped structure around the equator of the pulsar. This shape was in line with scientists’ expectations.
“This IXPE X-ray polarization measurement adds a missing piece of the Vela pulsar wind nebula puzzle,” said Dr. Alessandro Di Marco, a researcher at Italy’s National Institute for Astrophysics/Institute for Space Astrophysics and Planetology.
“By mapping with unprecedented resolution, IXPE unveils the magnetic field in the central region, showing agreement with results obtained from radio images of the outer nebula.”
“With IXPE, we are using extreme objects like Vela as a laboratory to investigate some of the most pressing questions in astrophysics, such as how particles get catapulted to near the speed of light long after a star has exploded,” said Dr. Phil Kaaret, a senior scientist at NASA’s Marshall Space Flight Center.
The findings were published in the journal Nature.
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F. Xie et al. 2022. Vela pulsar wind nebula X-rays are polarized to near the synchrotron limit. Nature 612, 658-660; doi: 10.1038/s41586-022-05476-5
Source : Breaking Science News