Black holes can trap matter and light inside once it gets too close and enters its point of no return, called the event horizon. These particles get locked away from the universe and never to be seen again. Streams of gas send out one last flare of light before it totally disappears.
It would have been nice to see it closer, but these death dives are too far away to be seen directly. Luckily, astronomers have developed a new technique for detecting the panic cries of help by those gasses. Scientists are using a method in testing humanity's knowledge of gravity in the most extreme environment of the universe.
To figure out how close anything can be to the black hole without attracting any danger, physicists looked at specific features of the light surrounding it, using a threshold called the Innermost Stable Circular Orbit (ISCO).
Passing Through the Event Horizon
According to LiveScience, the black hole has an invisible line-in-the-sand across which no one should cross, or else they get stuck inside it for the rest of the time. Nothing, not even light, can pass through the event horizon or it can no longer return to the universe. The gravity of the black hole is too strong within that region.
However, the outside part of the black hole is just cool. Sometimes, a black hole can have a mass of the sun or smaller ones in the galaxy that are billions of times heavier for the true monsters roaming the cosmos.
Many stuff in the universe finds itself orbiting around black holes. But once these materials get caught with the gravity of the black hole, they begin the journey toward the and. The stuff that falls toward the black hole tends to get squeezed into a razor-thin band known as an accretion disk, which spins endlessly, powered by heat, friction, and magnetic and electric forces causing it to glow brightly.
Some massive black holes have accretion disks around them that glow so intensely outshining millions of individual galaxies, that they get a new name: the active galactic nuclei (AGN). After some time, the accretion disk loses its rotational energy because of materials rubbing against each other.
Two Choices in Remaining in the Placid Orbit
As someone gets closer to the center of the black hole, it reaches a point where all hopes of stability disappear against the rocks of gravity. It is so extreme that once someone reaches this region, they cannot remain in placid orbit.
The researchers of the study highlighted two options that you can use. One is to use other sources of energy to propel itself away to safety. The second one applies to a hapless chunk of gas, wherein people are doomed to fall freely toward the endless darkness.
Einstein's theory of relativity confirms the innermost stable circular orbit. However, even with the general relativity theory's success, there is no evidence yet to verify the existence of ISCO and whether it conforms to the predictions of general relativity.
Taking Advantage of the Dying Light to Study ISCO
Recently, a team of astronomers published an article in the Monthly Notices of the Royal Astronomical Society. It describes how to take advantage of the dying light to learn more about the ISCO.
The technique that they used relies mainly on the reverberation mapping, in which it measures the structure of the broad swath of X-ray light that shines in all directions away from the black hole. These emissions are seen all the way from Earth, but details of the accretion disk structure get lost in the blaze of the X-ray glory.
Moreover, researchers used sophisticated computer simulations to see how the gas movement in ISCO affects the emission of X-rays, both nearby and outer gas. They found that the future generation of X-ray telescopes should be able to confirm the existence of ISCO and test if it agrees with predictions of general relativity.
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