Located 6,500 light-years away in the constellation of Taurus, the Crab Nebula and its pulsar formed in a supernova whose light reached Earth in July 1054.
This image of the Crab Nebula combines data from IXPE in magenta and NASA’s Chandra X-ray Observatory in dark purple. Image credit: IXPE / NASA / Chandra / CXC / SAO / K. Arcand / L. Frattare.
In the year 1054 CE, Chinese astronomers were startled by the appearance of a new star, so bright that it was the brightest object in the night sky, second only to the Moon, and was visible in broad daylight for 23 days.
The stellar explosion was also recorded by Japanese, Arabic, and Native American stargazers.
Today, the Crab Nebula is visible at the site of that bright star.
Also known as Messier 1, M1, NGC 1952 and Taurus A, it lies approximately 6,500 light-years away in the constellation of Taurus.
The Crab Nebula was first identified in 1731 by English doctor, electrical researcher and astronomer John Bevis and was rediscovered in 1758 by French astronomer Charles Messier.
It derived its name from its appearance in a drawing made by Irish astronomer Lord Rosse in 1844.
The Crab pulsar, also known as PSR B0531+21, is the central star in the Crab Nebula.
It is a young neutron star about 15.5 miles across, but it contains the mass of nearly one million Earths.
Now rotating 30 times a second, the pulsar emits beams of radio waves that, like a lighthouse, produce flashes each time it rotates.
“What makes science so beautiful and exciting is that for those few moments, you’re seeing something that no one has ever seen before,” said Dr. Martin Weisskopf, an emeritus astronomer at NASA’s Marshall Space Flight Center who studied the Crab Nebula in 1971 using a sounding rocket.
Nearly every recent large telescope has pointed to the Crab Nebula to better understand this mysterious supernova remnant.
But only NASA’s Imaging X-ray Polarimetry Explorer (IXPE) can study X-rays from the nebula in terms of polarization, a measure of the organization of electromagnetic fields.
“The Crab Nebula is one of the most-studied high-energy astrophysical objects in the sky,” said Dr. Michela Negro, a researcher at NASA’s Goddard Space Flight Center affiliated with the University of Maryland, Baltimore, and co-author of a paper published in the journal Nature Astronomy.
“So it is extremely exciting that we could learn something new about this system by looking through IXPE’s ‘polarized lenses’.”
Across the entire nebula, IXPE found about the same average polarization as Dr. Weisskopf and his colleagues did in the 1970s.
But with more sophisticated instruments, IXPE was able to refine the angle of polarization and examine the differences in polarization across the entire object.
The astronomers see areas of much polarization in the outer regions of the nebula, light-years away from the pulsar, where polarization is lower.
This enabled them to investigate not just X-rays from the Crab Nebula but also those coming from the pulsar itself, or the sphere of magnetic fields around it.
The findings suggest that those X-rays originate in the outer magnetic field region, called the ‘wind’ region, although exactly where and how is still unknown.
Within the magnetic field, shocks generated by the pulsar’s ‘wind’ are propelling particles close to the speed of light.
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N. Bucciantini et al. Simultaneous space and phase resolved X-ray polarimetry of the Crab pulsar and nebula. Nat Astron, published online April 6, 2023; doi: 10.1038/s41550-023-01936-8
