ISRO and IIT Guwahati discover new challenges in theories of X-ray pulsars
Researchers from IIT Guwahati and the Indian Space Research Organisation (ISRO) have made a surprising discovery that could change our understanding of X-ray pulsars. They found that the X-rays emitted by Swift J0243.6+6124, the first known galactic ultraluminous X-ray pulsar, exhibit an unexpectedly low level of polarization. This pulsar, located in our galaxy, exhibits only 3 percent polarization in its X-rays, a figure significantly lower than what current theories predict.
The mystery of Swift J0243.6+6124 revealed
Fast J0243.6+6124 was first identified during an intense X-ray burst in 2017-2018 by NASA’s Swift spacecraft. Since then, it has become a major subject of study for astronomers trying to understand the nature of ultraluminous X-ray sources (ULXs). ULXs are typically associated with intermediate-mass black holes, but some, such as Swift J0243.6+6124, are thought to be pulsars.
Pulsars are a type of neutron star, the remains of massive stars that have collapsed under their own gravity. These objects are incredibly dense, with a mass comparable to that of the sun, but squeezed into a space about the size of a city.
Unexpected findings and their implications
Using data from NASA’s Imaging X-ray Polarimetry Explorer (IXPE), along with the Neutron Star Interior Composition ExploreR (NICER) and the Nuclear Spectroscopic Telescope Array (NuSTAR) missions, researchers studied the polarization of the X-rays of Swift J0243.6+6124 during its active phase in 2023.
The findings revealed that the X-rays were only 3% polarized, much lower than the levels predicted by existing models. The discovery challenges long-held assumptions about how X-rays behave when they interact with the strong magnetic fields around neutron stars in binary systems.
Expert insights on the discovery
Dr. Anuj Nandi of ISRO emphasized the importance of these findings, noting that the low polarization observed in Swift J0243.6+6124 could lead to a re-evaluation of current theories about the radiation behavior of neutron stars. According to Dr. Nandi, the capabilities of the IXPE mission played a crucial role in detecting these low polarization levels, which appear to vary with the emitted X-ray pulses.
Prof. Santabrata Das from IIT Guwahati also commented on the significance of this discovery. He explained that the unexpectedly low polarization suggests that our understanding of the magnetic fields around neutron stars and the processes that govern X-ray emission needs to be updated. This could have far-reaching implications for future studies of similar X-ray sources in our galaxy and beyond.
A new path for future research
The discovery by IIT Guwahati and ISRO opens new doors for studying X-ray pulsars and other similar cosmic phenomena. As scientists continue to explore the mysteries of the universe, this unexpected discovery is likely to inspire further research and lead to a deeper understanding of the complex forces at work in space.
