Echoing black holes found in the Milky Way

(ORDO NEWS) — Echoes of light bouncing off dense clouds of matter around active black holes are helping astronomers better understand the bizarre space-time in the vicinity of these extreme objects.

Within the Milky Way, astronomers have just discovered eight new examples of such echolocating black holes. Previously, only two were discovered within our galaxy.

Having so many of these holes so close to home allows us to take a much closer look at these amazing objects, with the unique insight into black hole physics they have to offer.

Stellar-mass black holes – those formed from the collapse of a massive stellar core – are considered fairly common in the Milky Way.

There are up to a billion of them in the galaxy, but it is quite difficult to detect them; to date, we have identified only a few. This is because, if they are not active, they do not emit any radiation that we could detect. They are virtually invisible.

However, when black holes are active, it’s a different story. An active black hole is one that has caught something in its gravitational web and is gradually consuming it.

The material forms an accretion disk of dust and gas that spins around the black hole and falls into it, much like water swirls and rolls down a sewer. Crazy frictional and gravitational interactions generate intense heat and light, causing the area around the black hole to glow.

In rare black holes, we can also observe an amazing phenomenon. From time to time, the region inside the rim of the accretion disk closest to an active supermassive black hole flashes brightly – when this flash of light reaches the dust, it reflects back – an echo.

A team of researchers led by astrophysicist Jingyi Wang of the Massachusetts Institute of Technology used a new automated tool called the Reverberation Machine to analyze all archived data from NASA’s NICER X-ray observatory in search of signature black hole echoes.

As a result of the search, eight systems were discovered – binary stars containing a black hole, with a binary companion star, which is gradually being torn apart and devoured by a black hole.

“We’re seeing new signs of reverb in eight sources,” says Wang. “The mass of black holes varies from five to 15 times the mass of the Sun, and they are all in binary systems with ordinary low-mass stars similar to the Sun.”

Although rare, these echoes can reveal a lot about the environment around a black hole. Light from both the initial flash and the echo can be analyzed to measure the space between the black hole and the dust, much like a bat uses echolocation to navigate its environment.

Echoes from black holes can also be used to study how a black hole’s corona and accretion disk change as the black hole “feeds”. The corona is a region of scalding hot electrons between the inner edge of the accretion disk and the event horizon.

Next, the team analyzed 10 X-ray binaries, dividing the data into groups with the same time delays between the initial X-ray burst and the echo light. This allowed them to track changes in the X-ray echoes and get a big picture of how a black hole changes during an X-ray outburst.

At first, the black hole is in a “hard” state, generating a corona and emitting high-speed plasma jets from regions above its poles. When these processes dominate the energy profile of a black hole, the time intervals between X-ray bursts and their echoes are short, on the millisecond scale.

This state lasts for several weeks, after which a “soft” state sets in, dominated by lower-energy X-rays from the accretion disk. During this transition, the time intervals between bursts and echoes lengthen.

Since the speed of light is constant, this growing time interval indicates that the distance between the corona and the disk is increasing.

The team thinks this could mean that the corona is expanding upward and outward as the feeding event ends and the black hole subsides until the next tide of material is taken from its stellar companion.

It’s not entirely clear yet, but the results of the study have implications not only for understanding these small kinds of black holes, but also the supermassive giants that can be found in the cores of galaxies. This, in turn, can help us better understand the evolution of the universe.

“The role of black holes in the evolution of galaxies is an unresolved issue in modern astrophysics,” says MIT physicist Erin Cara, who has been working on converting black hole echoes into sound, as shown in the video above.

Interestingly, these binary black holes appear to be “mini” supermassive black holes, and so by understanding the outbursts in these small, nearby systems, we can understand how similar outbursts of supermassive black holes affect the galaxies they reside in. “.

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