MATHEMATICAL SCIENCES

Do the mounted “donuts” around the black hole dance? Scientists introduce new methods to expand the detection of larger areas of black holes


In 2019, astronomers captured the first photograph of a black hole, shocking the world. This is an image of a black hole shadow in the giant galaxy Messier 87 (M87), observed by the Black Hole Event Horizon Telescope Collaboration Group (EHT), bringing a wealth of information to astronomy and gravity.

“What else can we learn from these beautiful images?” This is a question that Shu Jing, a researcher at the Institute of Theoretical Physics of the Chinese Academy of Sciences, has been pondering.

Recently, Shu Jing’s team, in conjunction with research teams inside and outside the world, used changes in polarization images to give a new constraint to the coupling between a new particles called axions and visible photons, reaching areas that had not been explored before. The study was published in the latest issue of the journal Nature Astronomy.

Use the “heaviest” black hole to find the “lightest” particles

In 2019, combined with observations from telescopes around Earth, the EHT collaboration released a photo of an extremely high-resolution supermassive black hole, M87.

The shiny “donut”-like structure comes from radiation from accretion streams around the black hole — the black hole swallows up the light in the central region, creating a large shadow inside the “donut”. Two years later, the EHT collaboration updated the same image, bringing a finer structure to the original — textured lines representing the polarization direction of the line (EVPA), the black hole’s online polarized light effect like a “mounted flower” pattern, known as the “doughnut” version of the “mounted” version.

These findings and photographs give the most direct evidence of a black hole and reveal a magnetic field outside M87. The more important scientific significance is that the discovery of black holes has provided a new research method for many astrophysical and fundamental physical problems.

For example, direct imaging of a black hole could be used as a “probe” for extremely light particles.

In 1969, a thought experiment done by the famous mathematician and physicist Roger Penrose proposed that if someone threw a stone into a fast-spinning black hole, the stone had a chance to escape at a greater speed than before, and the extra energy it carried came from the black hole’s rotation.

Shu Jing, the corresponding author of the paper, told China Science Daily that when considering wave-particle duality in quantum mechanics (particles or quanta have both particle and wave properties), we can replace the stone with waves outside the rotating black hole.

“Waves can form dense clouds by extracting angular momentum from black holes, a process known as a super-radiation mechanism. In order for this process to occur, the Compton wavelength of the boson is required to be the same as the event horizon of the black hole. Thus, supermassive black holes become natural detectors for extremely light particles!” Shu Jing said.

Axis drive “dance”

“We’re fascinated by the idea that very light particles can aggregate outside a black hole. We realized that if extremely light shafts existed and interacted with visible light, they would make the ‘donuts’ of the mounting dance! Shu Jing said.

In 2020, Shu Jing’s team and collaborators published an article in the Physical Review Letters, pointing out that EHT’s polarization data is expected to explore the existence of ultra-light mass axion dark matter, which also has a profound impact on the field of particle physics, and the study also proposed a theoretical scheme for the axle to make the “doughnut” of the mounted flower dance.

In fact, of the various very light particles that go beyond the predictions of the Standard Model of particle physics, the axion is one of the most important candidates. Finding axions is one of the top priorities of particle physics and is widely predicted in many fundamental theories such as string theory. Axions are also a perfect candidate for cold dark matter , because in the very light mass window , some of the small-scale problems of galaxies have the potential to be solved by the flat distribution of axons at the center of the galaxy.

Supermassive black holes are a “weapon” for exploring the axions near black holes. When the heaviest celestial body is combined with the possible lightest mass shaft, a wonderful phenomenon occurs. That is, the light mass axion forms a cloud near the black hole, and the black hole forms a gravitational atomic system. The axion cloud attached to the black hole’s event horizon will reach a very high density in the process of continuously extracting the rotation energy of the black hole, far exceeding the dark matter gas near the solar system.

“In addition to the pure gravitational effect, the presence of axions can also cause additional periodic rotations in the direction of the polarization of the line, with cycles between 5 and 20 days. The change in polarization angle is manifested as a wave propagating in the direction of a bright halo, when the dance of the mounted pattern seems to have a specific pattern, rather than a random walk like a ‘drunkard’. Shu Jing told China Science Daily.

Chen Yifan, one of the authors of the paper and a postdoctoral fellow at the Institute of Theoretical Physics, explained that the so-called “dancing” refers to the fact that the “mounted” version of the black hole oscillates in a specific form, rotates in a fixed cycle in time, and has a special dance step around the direction of the doughnut in space. “We can confirm whether there is a ‘dance’ of polarization angles caused by axons by comparing the distribution of polarization near the black hole and their evolution over time.”

In the study, EHT measured the linear polarization of radiation emitted around M87 for 4 consecutive days, providing a high-resolution image of the linear polarization direction for 4 days, which is exactly the information the researchers needed to explore the axions.

Shu Jing said that using the different situations of the 4-day change of the mounting pattern, we can make the coupling between the axion and the photon break through to an area that has not been explored before. “‘Dancing’ is the signal form we predict if the axis exists, and if we don’t see the form of ‘dancing’, we can limit the parameter range of the axion, which is stronger than the previous limit.”

Expect more data to probe more mysteries

“To reduce the uncertainty of the turbulence change of the accretion flow, we introduced a new analysis strategy that uses the difference between two consecutive days as a visual measurement to limit the change in the direction of linear polarization caused by the axis.” Chen Yifan said that in the future, by providing more detailed data, especially more continuous-time observations and better spatial resolution, a larger parameter space can be detected.

Shu Jing said that this is the first time that the theory proposes that the black hole event horizon telescope detects the ultra-light new particle of the axion, and has made practical observations with collaborators, which is a very close combination of theory and experiment.

Axions cause polarization angles to “dance” (Courtesy of the Department of Physics, University of Utah)

“I’m more than happy to suggest publishing this paper.” Reviewers spoke highly of the study’s ultimate constraint on the axon-photon coupling constant to date, 1-2 orders of magnitude above the previous limit, a powerful application of EHT data to solve problems of interest to the contemporary particle physics community. The technical strategy employed could be on higher quality M87 data observed by EHT in the future, as well as other supermassive black hole data. (Source: China Science Daily Han Yangmei)

Related paper information:https://doi.org/10.1038/s41550-022-01620-3



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