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Wednesday, June 7, 2023

Scientists map gusty winds in a far-off neutron star system » MIT Physics

The 2D map of this “disk wind” could reveal clues to galaxy formation.

An accretion disk is a colossal whirlpool of fuel and dirt that gathers round a black gap or a neutron star like cotton sweet because it pulls in materials from a close-by star. Because the disk spins, it whips up highly effective winds that push and pull on the sprawling, rotating plasma. These huge outflows can have an effect on the environment of black holes by heating and blowing away the fuel and dirt round them.

At immense scales, “disk winds” can supply clues to how supermassive black holes form complete galaxies. Astronomers have noticed indicators of disk winds in lots of techniques, together with accreting black holes and neutron stars. However thus far, they’ve solely ever glimpsed a really slender view of this phenomenon.

Now, MIT astronomers have noticed a wider swath of winds, in Hercules X-1, a system during which a neutron star is drawing materials away from a sun-like star. This neutron star’s accretion disk is exclusive in that it wobbles, or “precesses,” because it rotates. By profiting from this wobble, the astronomers have captured various views of the rotating disk and created a two-dimensional map of its winds, for the primary time.

The brand new map reveals the wind’s vertical form and construction, in addition to its velocity — round a whole bunch of kilometers per second, or about 1,000,000 miles per hour, which is on the milder finish of what accretion disks can spin up.

If astronomers can spot extra wobbling techniques sooner or later, the staff’s mapping method may assist decide how disk winds affect the formation and evolution of stellar techniques, and even complete galaxies.

“Sooner or later, we may map disk winds in a variety of objects and decide how wind properties change, for example, with the mass of a black gap, or with how a lot materials it’s accreting,” says Peter Kosec, a postdoc in MIT’s Kavli Institute for Astrophysics and Area Analysis. “That may assist decide how black holes and neutron stars affect our universe.”

Kosec is the lead writer of a examine showing right now in Nature Astronomy. His MIT co-authors embody Erin Kara, Daniele Rogantini, and Claude Canizares, together with collaborators from a number of establishments, together with the Institute of Astronomy in Cambridge, U.Okay.

Fastened sight

Disk winds have most frequently been noticed in X-ray binaries — techniques during which a black gap or a neutron star is pulling materials from a much less dense object and producing a white-hot disk of inspiraling matter, together with outflowing wind. Precisely how winds are launched from these techniques is unclear. Some theories suggest that magnetic fields may shred the disk and expel among the materials outward as wind. Others posit that the neutron star’s radiation may warmth and evaporate the disk’s floor in white-hot gusts.  

Clues to a wind’s origins could also be deduced from its construction, however the form and extent of disk winds has been troublesome to resolve. Most binaries produce accretion disks which can be comparatively even in form, like skinny donuts of fuel that spins in a single airplane. Astronomers who examine these disks from far-off satellites or telescopes can solely observe the consequences of disk winds inside a set and slender vary, relative to their rotating disk. Any wind that astronomers handle to detect is due to this fact a small sliver of its bigger construction.

“We are able to solely probe the wind properties at a single level, and we’re fully blind to every little thing round that time,” Kosec notes.

In 2020, he and his colleagues realized that one binary system may supply a wider view of disk winds. Hercules X-1 has stood out from most identified X-ray binaries for its warped accretion disk, which wobbles because it rotates across the system’s central neutron star.

“The disk is de facto wobbling over time each 35 days, and the winds are originating someplace within the disk and crossing our line of sight at completely different heights above the disk with time,” Kosec explains. “That’s a really distinctive property of this technique which permits us to higher perceive its vertical wind properties.”

A warped wobble

Within the new examine, the researchers noticed Hercules X-1 utilizing two X-ray telescopes — the European Area Company’s XMM Newton and NASA’s Chandra Observatory.

“What we measure is an X-ray spectrum, which suggests the quantity of X-ray photons that arrive at our detectors, versus their power. We measure the absorption strains, or the dearth of X-ray mild at very particular energies,” Kosec says. “From the ratio of how robust the completely different strains are, we are able to decide the temperature, velocity, and the quantity of plasma throughout the disk wind.”

With Hercules X-1’s warped disk, astronomers have been in a position to see the road of the disk transferring up and down because it wobbled and rotated, much like the way in which a warped report seems to oscillate when seen from edge-on. The impact was such that the researchers may observe indicators of disk winds at altering heights with respect to the disk, reasonably than at a single, fastened top above a uniformly rotating disk.

By measuring X-ray emissions and the absorption strains because the disk wobbled and rotated over time, the researchers may scan properties such because the temperature and density of winds at varied heights with respect to its disk and assemble a two-dimensional map of the wind’s vertical construction.

“What we see is that the wind rises from the disk, at an angle of about 12 levels with respect to the disk because it expands in house,” Kosec says. “It’s additionally getting colder and extra clumpy, and weaker at better heights above the disk.”

The staff plans to match their observations with theoretical simulations of varied wind-launching mechanisms, to see which may greatest clarify the wind’s origins. Additional out, they hope to find extra warped and wobbling techniques, and map their disk wind buildings. Then, scientists may have a broader view of disk winds, and the way such outflows affect their environment — significantly at a lot bigger scales.

“How do supermassive black holes have an effect on the form and construction of galaxies?” poses Erin Kara, the Class of 1958 Profession Growth Assistant Professor of Physics at MIT. “One of many main hypotheses is that disk winds, launched from a black gap, can have an effect on how galaxies look. Now we are able to get a extra detailed image of how these winds are launched, and what they seem like.”

This analysis was supported, partly, by NASA.

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