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| Scientists have unveiled significant patterns of X-ray polarization within a black hole system | ||
Figure 1: Illustrated in the image is a black hole encompassed by an accretion disk composed of intensely heated dust, gas, and plasma.
A group of international scientists, led by Dr Divya Rawat, detected, for the first time, polarized emission from the matter before it disappears as it falls into a black hole source known by the name 4U 1630-47. The international team used publicly available data from two NASA’s satellites, the Imaging X-ray Polarimetry Explorer (IXPE) and the Neutron Star Interior Composition Explorer (NICER), for this discovery.
Since light cannot escape from a black hole, we cannot observe them directly. However, some black holes are members of a binary system (two objects orbiting around each other), with a normal star orbiting around the black hole. If a normal star is very close to the black hole, its outer layers will be stripped out by the strong gravitational pull of the black hole that literally eats the star. As it falls, the material from the star forms a disk before it is devoured by the black hole in a process called “accretion”. The international team measured the X-ray component of the light from that disk and discovered that the radiation is emitted at a preferred angle of 18 degrees in the sky. This significant finding is published in the Astrophysical Journal Letters (ApJL), a prestigious international journal.
Polarization occurs when the electromagnetic waves line up and vibrate in a specific direction. Normally, electromagnetic waves move in various directions, but when they become polarized, they synchronize and move in a specific plane. In black hole binary systems, various phenomena can lead to polarization of X-ray radiation. By studying the angle and amount of polarization, one can gain insights into the processes occurring in regions with strong gravity and also investigate the geometry of the accretion region.
Dr. Divya Rawat, the lead author of the study from the Inter-University Centre for Astronomy and Astrophysics (IUCAA), explains, “In a groundbreaking achievement, we have observed that 8% of the X-ray light emitted by the infalling material in the black-hole binary source 4U 1630-47 is polarized. This discovery allows us to deduce the shape and orientation of the accretion disk in this black-hole binary system. In conjunction with the upcoming Indian X-ray Polarimeter Satellite (XPoSat) mission, which will have higher coverage of the X-ray band than IXPE, we will explore different black-hole binary sources in a more detailed manner under varying conditions, which will provide invaluable and totally new insights into the structure of the accretion region around the black hole.”
Dr. Akash Garg, another member of the team from IUCAA, emphasizes, “This discovery holds great significance as it introduces the new aspect of polarization to the existing understanding of the characteristics of black hole systems. It will contribute to our improved comprehension of the dynamics of the material that falls onto the black hole.”
Based on X-ray observations, scientists have proposed a widely accepted idea about the arrangement of matter around a black hole. According to this theory, there is an outer flat disk and an inner hot region called the corona, with temperatures of 100 millions degrees or more, near the black hole. When the hot region is larger compared to the disk region, the black hole emits powerful radio jets. However, these theories are mainly based on studying the energy spectrum and timing of the radiation. We still need a definitive study to solve the longstanding mystery of the exact geometry of matter falling into a black hole.
The other member of the team is Prof. Mariano Méndez from the University of Groningen in the Netherlands. He says, “In previous studies, measurements of X-ray polarization in other sources were associated with the corona or jet in those systems. However, in this observation of 4U 1630-47, the corona is notably absent, and the jet in black hole binaries is suppressed in the absence of the corona. We speculate that the polarized emission in 4U 1630-47 originates from the accretion disk. This had not been seen previously, and new models will be needed to explain our results.”
Scientific background:
Polarization occurs when the electromagnetic waves line up and vibrate in a specific direction. Normally, electromagnetic waves move in various directions, but when they become polarized, they synchronize and move in a specific plane. In black hole binary systems, various phenomena can lead to polarization of X-ray radiation. By studying the angle and amount of polarization, one can gain insights into the processes occurring in regions with strong gravity and also investigate the geometry of the accretion region.
Dr. Divya Rawat, the lead author of the study from the Inter-University Centre for Astronomy and Astrophysics (IUCAA), explains, “In a groundbreaking achievement, we have observed that 8% of the X-ray light emitted by the infalling material in the black-hole binary source 4U 1630-47 is polarized. This discovery allows us to deduce the shape and orientation of the accretion disk in this black-hole binary system. In conjunction with the upcoming Indian X-ray Polarimeter Satellite (XPoSat) mission, which will have higher coverage of the X-ray band than IXPE, we will explore different black-hole binary sources in a more detailed manner under varying conditions, which will provide invaluable and totally new insights into the structure of the accretion region around the black hole.”
Dr. Akash Garg, another member of the team from IUCAA, emphasizes, “This discovery holds great significance as it introduces the new aspect of polarization to the existing understanding of the characteristics of black hole systems. It will contribute to our improved comprehension of the dynamics of the material that falls onto the black hole.”
Based on X-ray observations, scientists have proposed a widely accepted idea about the arrangement of matter around a black hole. According to this theory, there is an outer flat disk and an inner hot region called the corona, with temperatures of 100 millions degrees or more, near the black hole. When the hot region is larger compared to the disk region, the black hole emits powerful radio jets. However, these theories are mainly based on studying the energy spectrum and timing of the radiation. We still need a definitive study to solve the longstanding mystery of the exact geometry of matter falling into a black hole.
The other member of the team is Prof. Mariano Méndez from the University of Groningen in the Netherlands. He says, “In previous studies, measurements of X-ray polarization in other sources were associated with the corona or jet in those systems. However, in this observation of 4U 1630-47, the corona is notably absent, and the jet in black hole binaries is suppressed in the absence of the corona. We speculate that the polarized emission in 4U 1630-47 originates from the accretion disk. This had not been seen previously, and new models will be needed to explain our results.”
Article:
DOI: 10.3847/2041-8213/acd77b
Research contacts:
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Dr. Divya Rawat Post-Doctoral fellow, AstroSat Science Support Cell, IUCAA, Pune E-mail: divya.rawat_at_iucaa.in Phone: +91-020-25604100 |
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Dr. Akash Garg, Post-Doctoral fellow, IUCAA, Pune E-mail: akash.garg_at_iucaa.in Phone: +91-020-25604100 |
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Prof. Mariano Méndez Kapteyn Astronomical Institute, Netherlands E-mail: mariano_at_astro.rug.nl |