Oct. 18 () –
For the first time, astronomers have measured and mapped polarized X-rays from the remains of an exploded star. using the IXPE satellite (Imaging X-ray Polarimetry Explorer) from NASA.
the findings, which come from observations of a stellar remnant called Cassiopeia Ashed new light on the nature of young supernova remnants, which accelerate particles close to the speed of light.
Released on December 9, 2021, IXPE, a collaboration between NASA and the Italian Space Agency, it is the first satellite that can measure the polarization of X-ray light with this level of sensitivity and clarity.
All forms of light, from radio waves to gamma rays, can be polarized. Unlike the polarized sunglasses we wear to reduce glare from sunlight bouncing off a wet road or windshield, IXPE detectors map the traces of incoming X-ray light (shown in turquoise in the image below). ).
Scientists can use these individual track records to discover polarization, which tells the story of what the X-rays went through.
Cassiopeia A (Cas A for short) was the first object that IXPE observed after it began collecting data. One of the reasons Cas A was selected is that its shock waves, like a sonic boom generated by a jet, are some of the fastest in the Milky Way. The shock waves were generated by a supernova explosion that destroyed a massive star after it collapsed. The light from the explosion swept across the Earth more than three hundred years ago.
“Without IXPE, we have been missing crucial information about objects like Cas A,” he said. it’s a statement Pat Slane at the Center for Astrophysics | Harvard & Smithsonian, who leads the IXPE research on supernova remnants. “This result is teaching us about a fundamental aspect of the remains of this exploded star: the behavior of their magnetic fields“.
Magnetic fields, which are invisible, push and attract moving charged particles, such as protons and electrons. Closer to home, they are in charge of keeping the magnets glued to the kitchen fridge. Under extreme conditions, such as an exploding star, magnetic fields can propel these particles near the speed of light.
Despite their superfast speeds, particles entrained by shock waves in Cas A don’t fly away from the supernova remnant. because they are trapped by magnetic fields in the wake of shocks. The particles are forced to spiral around magnetic field lines, and the electrons emit a type of intense light called “synchrotron radiation,” which is polarized.
By studying the polarization of this light, scientists can reverse-engineer what’s going on inside Cas A at very small scales, details that are difficult or impossible to observe otherwise. The polarization angle tells us about the direction of these magnetic fields. If the magnetic fields near the shock fronts are highly entangled, the chaotic mixing of radiation from regions with different magnetic field directions will generate a smaller amount of polarization.
Previous studies of Cas A with radio telescopes have shown that radiosynchrotron radiation is produced in regions throughout almost the entire supernova remnant. The astronomers found that only a small amount of the radio waves were polarized, about 5%. They also determined that the magnetic field is oriented radially, like the spokes of a wheel, extending from near the center of the remnant to the edge.
Data from NASA’s Chandra X-ray Observatory, on the other hand, show that the X-ray synchrotron radiation comes mainly from thin regions along the shocks, near the remnant’s circular outer edge, where the remnants were predicted to be. magnetic fields would align with the shock Chandra and IXPE use different types of detectors and have different levels of angular resolution or sharpness. Released in 1999, Chandra’s first science image was also of Cas A.
Before IXPE, scientists predicted that X-ray polarization would be produced by magnetic fields. which are perpendicular to the magnetic fields observed by radio telescopes.
Instead, the IXPE data show that X-ray magnetic fields tend to align in radial directions even very close to shock fronts. The X-rays also reveal a smaller amount of polarization than radio observations did, suggesting that the X-rays they come from turbulent regions with a mixture of many different magnetic field directions.
“These IXPE results were not what we expected, but as scientists we love to be surprisedsays Dr. Jacco Vink of the University of Amsterdam and lead author of the paper describing the IXPE results on Cas A. “The fact that a smaller percentage of X-ray light is polarized is a very interesting property, and previously undetected, from Cas A.”
