NASA's IXPE successfully studies a distant white dwarf star for the first time in history
NASA's Imaging X-ray Polarization Explorer (IXPE) just studied a white dwarf for the first time ever. The study, according to NASA, involved using X-ray polarization—a feature unique to IXPE—to understand the geometry of energetic binary systems via the examination of a star called the intermediate polar EX-Hydrae.
A white dwarf represents the ultra-dense core of a star that has no more hydrogen fuel to fuse in its core but lacks the scale to turn into a supernova. Although only about the size of the planet Earth, such celestial bodies are as heavy as the Sun. EX Hydrae, the star system under investigation, is presently enjoying the luxury of gas "feeding" from its companion star. While the magnetic field around EX Hydrae is not powerful enough to focus all of the material coming from the companion star towards its poles, it is strong enough to continue adding mass to the hot, bright, rapidly spinning structure around it, called the accretion disk. It is because of this feature that EX Hydrae is classified as 'intermediate polar.' The matter that accumulates in the accretion disk gets heated to tens of millions of degrees, releasing gas and high-energy X-rays that were picked up by IXPE.
"NASA IXPE’s one-of-a-kind polarimetry capability allowed us to measure the height of the accreting column from the white dwarf star to be almost 2,000 miles high – without as many assumptions required as past calculations," MIT researcher and lead author of the study, Sean Gunderson, explained. "The X-rays we observed likely scattered off the white dwarf’s surface itself. These features are far smaller than we could hope to image directly and clearly show the power of polarimetry to ‘see’ these sources in detail never before possible."
The research, which is available online on The Astrophysical Journal, not only provides a new map for the understanding of high-energy binary systems in the galaxy but also enables NASA to predict how matter behaves under extreme gravity and magnetic pressure in other parts of the universe by mastering the geometry of EX Hydrae.
This breakthrough comes as yet another significant achievement for the IXPE mission. Not too long ago, the same observatory contributed to the resolution of a mystery surrounding the origin of X-rays in supermassive black holes that had lasted a long time. In what was the telescope's longest single observation ever, IXPE stared at the Perseus Cluster for more than 600 hours over a span of 60 days. More specifically, the observation focused on 3C 84 and its X-ray polarization properties, as it is an active galaxy that is not only a massive source of X-ray emission but is also reasonably close and bright. The study found that the X-rays in 3C 84 are a result of light gaining immense amounts of energy after bouncing off particles—a process known as inverse Compton scattering.
