astronomers better understand the wacky space-time present in these extreme objects thanks to echoing light moving off large amounts of material around active black holes.
astronomers have just identified eight new examples of these echoing black holes within the Milky Way. Previously, only two had been identified within our galaxy.
A larger number of individuals who are so close to home is allowing for a much greater exploration of these fascinating items, with the unique insight they can offer in black hole physics.
The black holes in Stellarmass that formed from the collapse of a massive stellar core are thought to be fairly common in the Milky Way.
There are as many as a billion of things moving around the galaxy, but they''re quite difficult to detect; to date, we''ve only identified a few individuals. That''s because, unless they''re active, they don''t emit any radiation we can detect. They''re effectively invisible.
When black holes are active, it''s a different story. An active black hole is one that has hidden something in its gravitational web and is gradually devouring it.
The material forms an accretion disk of dust and gas that swirls around the black hole and reaching it out, almost like water colliding and sliding down a drain. Extreme frictional and gravitational effects involved produce intense heat and light, causing the region around the black hole to glow.
When this flare of light hits the dust, we can also see a fascinating phenomenon at work. Every time and again, the area just inside the accretion disk closest to an active supermassive black hole flares brightly. It is then reflected back an echo.
A team of researchers used a new, well-known robotic device called the Reverberation Machine, to search all of NASA''s NICER X-ray observatory''s archival data, searching for clues.
This examination uncovered eight systems binaries with a black hole, each of which contains a binary companion star.
"We see new signs 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."
These echoes can enlighten a lot about the environment around a black hole, both the initial outburst and the echo, to measure the distance between the black hole and the dust, similar to that used by a bat to navigate its surroundings.
As the black hole "feeds," black hole echoes can be used to discover how a black hole''s corona and the accretion disk evolve. The corona is a region of scorchingly hot electrons between the inner edge of the accretion disk and the event horizon.
The group analyzed the ten X-ray emitting binary systems, dividing them into groups with similar time differences between the initial X-ray burst and the echoed light. This allowed them to see the changes in the X-ray echoes and develop a general picture of how the black hole changes during an X-ray outburst.
First, the black hole starts off in a "hard" state, producing a corona, and emitting high-speed jets of plasma from the areas over its poles. When these processes dominate the black hole''s energy profile, the time intervals between the X-ray bursts and their echos are short, on the scale of milliseconds.
This state lasts for a few weeks before settling down into a "soft" state, dominated by lower-energy X-rays from the accretion disk. During this transition, the time intervals between bursts and the echoes continue.
Because the speed of light is constant, this rising time lag suggests that the distance between the corona and the disk is increasing.
As the feeding event tails off and the black hole quietens down, the team believes this may imply that the corona expands upwards and outwards, causing the corona to gain momentum.
It''s not entirely clear yet, but the results have implications not only for understanding these small kinds of black holes, but also for understanding the supermassive behemoths found at the cores of galaxies. This, in turn, may aid us in advancing the Universe.
"In modern astrophysics, the role of black holes in galaxy evolution is an exceptional question," says MIT''s physicist Erin Kara, who is working on converting black hole echoes to sound."
"Interestingly, these black hole binaries appear to be''mini''''supermassive black holes, and thus by understanding outbursts in these small, nearby systems, we can understand how similar outbursts in supermassive black holes influence the galaxies in which they reside."
The Astrophysical Journal has published these findings.