Ouvindo os sons assustadores do Black Hole Echo – Pesquisa revela 8 novas fontes de Black Hole Echo

Nesta ilustração, um buraco negro puxa material de uma estrela próxima para um disco de acreção. Crédito: Aurore Simonnet e Goddard Space Flight Center da NASA

As novas descobertas ajudarão os cientistas a rastrear um[{” attribute=””>black hole’s evolution as it feeds on stellar material.

Tens of millions of black holes are strewn across our Milky Way galaxy. These gravitational wells of spacetime are so enormously powerful that infalling matter, and even light, can never escape. Except on rare instances when they feed, black holes are inherently dark. As a black hole absorbs gas and dust from an orbiting star, it can emit stunning bursts of X-ray radiation that bounce and reverberate off the inspiraling gas, briefly illuminating a black hole’s extreme surroundings.

Now MIT astronomers are looking for flashes and echoes from nearby black hole X-ray binaries — systems with a star orbiting, and occasionally being eaten away by, a black hole. They are analyzing the echoes from such systems to reconstruct a black hole’s immediate, extreme vicinity.

In a study appearing published on May 2, 2022, in The Astrophysical Journal, the researchers report using a new automated search tool, which they’ve named the “Reverberation Machine,” to comb through satellite data for signs of black hole echoes. In their search, they have discovered eight new echoing black hole binaries in our galaxy. Previously, only two such systems in the Milky Way were known to emit X-ray echoes.

In comparing the echoes across systems, the team has pieced together a general picture of how a black hole evolves during an outburst. Across all systems, they observed that a black hole first undergoes a “hard” state, whipping up a corona of high-energy photons along with a jet of relativistic particles that is launched away at close to the speed of light. The researchers discovered that at a certain point, the black hole gives off one final, high-energy flash, before transitioning to a “soft,” low-energy state.

This final flash may be a sign that a black hole’s corona, the region of high-energy plasma just outside a black hole’s boundary, briefly expands, ejecting a final burst of high-energy particles before disappearing entirely. These findings could help to explain how larger, supermassive black holes at the center of a galaxy can eject particles across vastly cosmic scales to shape a galaxy’s formation.

“The role of black holes in galaxy evolution is an outstanding question in modern astrophysics,” says Erin Kara, assistant professor of physics at MIT. “Interestingly, these black hole binaries appear to be ‘mini’ supermassive black holes, and so by understanding the outbursts in these small, nearby systems, we can understand how similar outbursts in supermassive black holes affect the galaxies in which they reside.”

The study’s first author is MIT graduate student Jingyi Wang; other co-authors include Matteo Lucchini and Ron Remillard at MIT, along with collaborators from Caltech and other institutions.

X-ray delays

Kara and her colleagues are using X-ray echoes to map a black hole’s vicinity, much the way that bats use sound echoes to navigate their surroundings. When a bat emits a call, the sound can bounce off an obstacle and return to the bat as an echo. The time it takes for the echo to return is relative to the distance between the bat and the obstacle, giving the animal a mental map of its surroundings.

In a similar fashion, the MIT team is looking to map the immediate vicinity of a black hole using X-ray echoes. The echoes represent time delays between two types of X-ray light: light emitted directly from the corona, and light from the corona that bounces off the accretion disk of inspiraling gas and dust.

The time when a telescope receives light from the corona, compared to when it receives the X-ray echoes, gives an estimate of the distance between the corona and the accretion disk. Watching how these time delays change can reveal how a black hole’s corona and disk evolve as the black hole consumes stellar material.

Echo evolution

In their new study, the team developed a search algorithm to comb through data taken by NASA’s Neutron star Interior Composition Explorer, or NICER, a high-time-resolution X-ray telescope aboard the International Space Station. The algorithm picked out 26 black hole X-ray binary systems that were previously known to emit X-ray outbursts. Of these 26, the team found that 10 systems were close and bright enough that they could discern X-ray echoes amid the outbursts. Eight of the 10 were previously not known to emit echoes.

“We see new signatures of reverberation in eight sources,” Wang says. “The black holes range in mass from five to 15 times the mass of the sun, and they’re all in binary systems with normal, low-mass, sun-like stars.”

As a side project, Kara is working with MIT education and music scholars, Kyle Keane and Ian Condry, to convert the emission from a typical X-ray echo into audible sound waves. Take a listen to the sound of a black hole echo here:

Crédito: Voz calculada por Kyle Keane e Erin Kara, MIT. Animação calculada por Michal Dovciak, ASU CAS.

Em seguida, os pesquisadores executaram o algoritmo em 10 binários de buracos negros e dividiram os dados em grupos com “recursos de tempo espectrais” semelhantes, ou seja, atrasos semelhantes entre os raios-X de alta energia e o eco reprocessado. Isso ajudou a rastrear rapidamente a mudança nos ecos de raios-X em cada estágio durante a erupção do buraco negro.

A equipe identificou uma coevolução em todos os sistemas. No estado “sólido” inicial, onde um halo e jato de partículas de alta energia dominam a energia do buraco negro, eles detectaram atrasos de tempo curtos e rápidos, da ordem de milissegundos. Esta condição difícil persiste por várias semanas. Então, a transição ocorre ao longo de vários dias, à medida que a coroa e os jatos desaparecem, o estado suave e os raios X de baixa energia controlam o disco de acreção do buraco negro.

Durante esse estado de transição difícil para suave, a equipe descobriu que o atraso de tempo aumentou em todos os 10 sistemas, o que implica que a distância entre a coroa e o disco também aumentou. Uma explicação é que a coroa pode se estender brevemente para fora e para cima, em uma explosão final de alta energia antes que o buraco negro termine a maior parte de sua refeição estelar e esfrie.

“Estamos apenas começando a usar esses ecos de luz para reconstruir ambientes mais próximos do buraco negro”, diz Kara. “Mostramos agora que esses ecos são comumente observados e podemos examinar as conexões entre o disco, o jato e a coroa de um buraco negro de uma nova maneira”.

Referência: “The NICER “The Echo Machine”: A Systematic Study of Time Delays in Black Hole X-ray Binaries” por Jinji Wang, Irene Cara, Matteo Luccini, Adam Ingram, Michel van der Kles, Guglielmo Mastrorio, Javier A. Thomas Dowser, Riley Connors, Andrew C. Fabian, James F. Steiner, Ron A. Remillard, Edward M. Caquet, Phil Oatley e Diego Altamerano, 2 de maio de 2022, Jornal Astrofísico.
DOI: 10.3847/1538-4357/ac6262

Esta pesquisa foi apoiada, em parte, pela NASA.