Several 'Echoing' Black Holes Have Just Been Discovered in The Milky Way

The light bouncing off the thick clouds of material around active black holes is helping to understand the weird space-time in the immediate vicinity of these extreme objects.

Astronomers have found eight new examples of black holes in the Milky Way. Only two had been identified before.

Having an expanded number so close to home allows a closer study of these fascinating objects, with the unique insight they can offer into black hole physics.

Black holes formed from the collapse of a massive stellar core are fairly common in the Milky Way.

We have only identified a few of the billion things that are drifting around the universe. Unless they are active, they don't emit any radiation. They are effectively invisible.

Black holes are not the same as they were before. An active black hole is one that is grabbing something in its web.

The material forms an accretion disk of dust and gas around the black hole and falls into it, like water sliding down a drain. The region around the black hole is glowing due to the insane heat and light generated by the interactions.

There is a fascinating phenomenon at work in rare black holes. When a flare of light reaches the dust, it is reflected back, and every now and again, the region just inside the rim of the accretion disk flares brightly.

A team of researchers used a new tool called the Reverberation Machine to look for signs of black hole echoes from archival data.

A search turned up eight systems containing a black hole, with a companion star being gradually stripped and devoured by the black hole.

The black holes range in mass from five to 15 times the mass of the Sun, and they are all in systems with normal, low-mass.

These echoes can tell us a lot about the environment around a black hole. The space between the black hole and the dust can be measured by analyzing the light from the beginning and the echo.

Black hole echoes can be used to study how black holes corona and accretion disk change as the black holes feeds. The corona is a region of hot electrons between the inner edge of the accretion disk and the event horizon.

The team divided the data into groups based on the time lags between the initial X-ray burst and the echoed light. They were able to track the changes in the X-ray echoes to develop a general picture of how the black hole changes.

The black hole starts off in a hard state, generating a corona and emitting high-speed jets of plasma from the regions over its poles. The time between the X-ray bursts and their echoes is short when these processes are dominating the black hole.

This state lasts for a few weeks, before calming down into a soft state dominated by lower-energy X-rays from the accretion disk. The time between the bursts and the echoes is longer during this transition.

The growing time lag suggests that the distance between the corona and the disk is shortening.

The team thinks that this could mean that the corona expands as the feeding event ends and the black hole quiets down, until the next feeding frenzy of material is stripped from its stellar companion.

The results have implications not just for understanding these small kinds of black holes, but also the super massive monsters that can be found at the core of galaxies. This could help us understand the evolution of the Universe.

The role of black holes in galaxy evolution is an outstanding question in modern astrophysics, according to physicistErin Kara of MIT, who has been working on converting black hole echoes to sound.

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 research has been published.