An accretion disk is a massive vortex of gas and dust that accumulates like cotton candy around a black hole or a neutron star as it absorbs matter from an adjacent star. Powerful winds created by the disk’s rotation push and pull on the plasma’s spherical, rotating surface.
By heating and removing the dust and gas surrounding black holes, these enormous outflows can have an impact on their surroundings. “Disk winds” can provide hints as to how supermassive black holes shape entire galaxies at enormous sizes.
Many systems including accreting black holes and neutron stars have disk winds that have been seen by astronomers. Yet, they have only ever had a very brief glimpse of this event up to this point. A wider swath of winds has now been seen by MIT astronomers in the system of Hercules X-1, where a neutron star is removing material from a sun-like star.
The accretion disk of this neutron star is unusual in that it wobbles or processes while rotating. The astronomers were able to collect several views of the rotating disk and produce a two-dimensional map of its winds by taking advantage of this wobbling.
The new map shows the wind’s vertical shape and structure as well as its velocity which is on the lower end of what accretion disks can spin up at approximately a million miles per hour or hundreds of kilometers per second.
The team’s mapping method could help astronomers understand how disk winds affect the birth and evolution of star systems and perhaps entire galaxies, if they are able to find more wobbling systems in the future. Peter Kosec says, a postdoc at MIT’s Kavli Institute for Astrophysics and Space Research (According to Scitechdaily)
“In the future, we could map disk winds in a range of objects and determine how wind properties change, for instance, with the mass of a black hole, or with how much material it is accreting. That will help determine how black holes and neutron stars influence our universe.”
A paper that appears in Nature Astronomy has Kosec as its principal author. Erin Kara, Daniele Rogantini and Claude Canizares are some of his MIT co-authors. Other writers come from various universities such as the Institute of Astrophysics in Cambridge, United Kingdom.
The situations in which a black hole or neutron star is squeezing matter from a less dense object and creating a white-hot disk of inspirational matter together with an outflowing wind are known as X-ray binaries and are where disk winds have most frequently been recorded.
It’s unknown exactly how winds are launched from these devices. Magnetic fields might tear the disk and blow some of the debris outside as wind. Others propose that white-hot gusts of radiation from the neutron star might heat and vaporize the disk’s surface.
It is possible to infer information about a wind’s origins from its structure, but it has been challenging to determine the shape and size of disk winds. The majority of binaries create accretion disks that are generally uniform in shape, resembling thin gas donuts that spin in a single plane.
Astronomers studying these disks from distant satellites or telescopes can only see the impact of disk winds relative to their revolving disk within a fixed and limited range. So any wind that astronomers are able to observe is only a tiny fragment of its whole structure. Kosec notes, According to Tech Explorist:
“We can only probe the wind properties at a single point, and we’re completely blind to everything around that point.”
He and his coworkers discovered in 2020 that one binary system may provide a more comprehensive perspective of disk winds. In contrast to most other known X-ray binaries, Hercules X-1 has a distorted accretion disk that wobbles as it revolves around the system’s primary neutron star. Kosec explains (as reported by Head Topics)
“The disk is really wobbling over time every 35 days, and the winds are originating somewhere in the disk and crossing our line of sight at different heights above the disk with time. That’s a very unique property of this system which allows us to better understand its vertical wind properties.”
In the latest research, the XMM Newton and Chandra X-ray telescopes of the European Space Agency and NASA were used to observing Hercules X-1. Kosec says, According to News 9 Live:
“What we measure is an X-ray spectrum, which means the amount of X-ray photons that arrive at our detectors, versus their energy. We measure the absorption lines, or the lack of X-ray light at very specific energies. From the ratio of how strong the different lines are, we can determine the temperature, velocity, and the amount of plasma within the disk wind.”
Astronomers were able to observe the warped disk of Hercules X-1 as it wobbled and rotated, much like how a warped record appears to oscillate when viewed from the edge-on. As a result, rather than at a single, set height above a uniformly rotating disk, the researchers could detect traces of disk winds at varying heights concerning the disk.
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The researchers could scan parameters like the temperature and density of winds at different heights with respect to its disk and create a two-dimensional picture of the wind’s vertical structure by analyzing X-ray emissions and the absorption lines as the disk wobbled and rotated over time. Kosec says (as reported by Tech Explorist)
“What we see is that the wind rises from the disk, at an angle of about 12 degrees with respect to the disk as it expands in space. It’s also getting colder and more clumpy, and weaker at greater heights above the disk.”
To determine which wind-launching mechanism better explains the origins of the wind, the team intends to compare their observations with theoretical models of other wind-launching mechanisms. They intend to find more twisted and wobbly systems farther out and map their disk wind structures.
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