PEEP INTO A BLACK HOLE

Black holes are points in space that are so dense they create deep gravity sinks. Beyond a certain region, not even light can escape the powerful tug of a black hole's gravity. And anything that ventures too close—be it star, planet, or spacecraft—will be stretched and compressed like putty in a theoretical process aptly known as spaghettification.

The idea of an object in space so massive and dense that light could not escape it has been around for centuries. Most famously, black holes were predicted by Einstein's theory of general relativity, which showed that when a massive star dies, it leaves behind a small, dense remnant core. If the core's mass is more than about three times the mass of the Sun, the equations showed, the force of gravity overwhelms all other forces and produces a black hole.

TYPES OF BLACK HOLES

There are four types of black holes: primordial black holes , stellar, supermassive & Miniature black holes.

1. Primordial Black Holes :

The smallest ones are known as primordial black holes. Scientists believe this type of black hole is as small as a single atom but with the mass of a large mountain.

2.Stellar Black Holes:

The most common type of medium-sized black holes is called "stellar." The mass of a stellar black hole can be up to 20 times greater than the mass of the sun and can fit inside a ball with a diameter of about 10 miles. Dozens of stellar mass black holes may exist within the Milky Way galaxy.

3.Supermassive Black Holes:

The largest black holes are called "supermassive." These black holes have masses greater than 1 million suns combined and would fit inside a ball with a diameter about the size of the solar system. Scientific evidence suggests that every large galaxy contains a supermassive black hole at its center. The supermassive black hole at the center of the Milky Way galaxy is called Sagittarius A. It has a mass equal to about 4 million suns and would fit inside a ball with a diameter about the size of the sun

4.Miniature Black Holes:

No one has ever discovered a miniature black hole, which would have a mass much smaller than that of our Sun. But it's possible that miniature black holes could have formed shortly after the "Big Bang," which is thought to have started the universe 13.7 billion years ago. Very early in the life of the universe the rapid expansion of some matter might have compressed slower-moving matter enough to contract into black holes.

BLACK HOLES FORMATION

In final stages, enormous stars go out with a bang in massive explosions known as SUPERNOVAE. Such a burst flings star matter out into space but leaves behind the stellar core. While the star was alive, nuclear fusion created a constant outward push that balanced the inward pull of gravity from the star's own mass. In the stellar remnants of a supernova, however, there are no longer forces to oppose that gravity, so the star core begins to collapse in on itself.

If its mass collapses into an infinitely small point, a black hole is born. Packing all of that bulk—many times the mass of our own sun—into such a tiny point gives black holes their powerful gravitational pull. Thousands of these stellar mass black holes may lurk within our own Milky Way galaxy.

Is a black hole a giant cosmic vacuum cleaner?

The answer to this question is "not really."

The gravity around a black hole remains normal unless you get extremely close. If the Sun suddenly became a black hole (which isn't actually possible),the Earth and all the other planets would continue to orbit it just as though nothing had changed.

The behavior of gravity doesn't change until an object approaches to the point where it's within a few times the radius of the event horizon, the boundary marking the region around a black hole from which not even light can escape. At that point, objects begin to lose the ability to maintain stable orbits, and inevitably spiral into the black hole.

So to return to our theoretical example, if the Sun became a black hole, objects would have to be as close as about 6.2 miles (10 km) to the black hole's center before they began spiraling in.

ANATOMY OF A BLACK HOLE

1.Accretion disk :

A disk of superheated gas & dust whirls around a black hole at immense speeds, producing electromagnetic radiations(like x-rays,optical,infrared & radio) that reveal the location of the black holes.Some of this material is doomed to cross the event horizon, while other parts may be forced to create jets.

2.Inner most stable orbit & Particle jet:

The inner edge of an accretion disk that last is the last place that material can orbit safely without the risk of falling into the black hole.

When a black hole feeds on stars, gas & dust, the produces jets of particles & radiation blasting out from the black hole's poles of near light speed.They can extend for thousand of light years into the space.

3.Photon sphere:

Although the black hole itself is dark, photons are emitted from nearby hot plasma in jets or an accretion disk. In absence of gravity this photons would travel in straight lines,but just outside the event horizon of a black hole, gravity is strong enough to bend their paths so that we see a bright ring surrounding a roughly circular dark "shadow".

The Event Horizon Telescope is hoping to see both the ring & shadow.

4.Event Horizon:

This is the radius around a singularity where matter & energy can't escape the black holes gravity:the point of no return.THIS IS THE BLACK PART OF THE BLACK HOLE.

5.Singularity:

At the very center of a black hole, matter has collapsed into a region of infinite density called a 'Singularity'. All the matter & energy that fall into the black hole ends up here. The prediction of infinite density by general theory of relativity is thought to indicate the break down of the theory where the quantum effects become important.

Entropy:

The first law relates the mass, rotation and charge of a black hole to its entropy. The entropy of a black hole is then related to the surface area of its event horizon. The second law again states that the entropy of a black hole system cannot decrease .

S = 1/4 c3k/Għ A

Information loss paradox:

This phenomenon states that the information a physical system has can be lost when it enters a black hole. The object that falls into a black hole, only keeps information about its spin, mass and charge. However, the quantum mechanics says that information cannot be lost. This makes it a paradox.

The firewall paradox:

The first is based on the Equivalence Principle of General Relativity. Because an observer is in free fall as they cross the black hole's event horizon, the equivalence principle says that there is no detectable difference between free fall and inertial motion, the observer shouldn’t feel extreme effects of gravity. The equivalence principle is only applicable in small region, tidal effects can also occur.

The second concept is based around quantum mechanics, and is called Unitarity, which conjectures that information that falls into a black hole is not irretrievably lost.

Finally, there is the assumption that the physics far away from a black hole obeys the same laws as here on earth. The laws may fail near the event horizon, or if not there, at the singularity itself. Obviously, we have problems testing this, but it is generally regarded as an inevitable consequence if you describe the universe using GR.

Temperature :

The most massive black holes in the Universe, the supermassive black holes with millions of times the math of the Sun will have a temperature of 1.4 x 10-14 Kelvin. That's low. Almost absolute zero, but not quite. A solar mass black hole might have a temperature of only .0.00000006 Kelvin .

Since MASS is INVERSELY PROPORTIONAL TO TEMPERATURE .

Simulation of Black Hole:

Gas glows brightly in this computer simulation of supermassive black holes only 40 orbits from merging. Models like this may eventually help scientists pinpoint real examples of these powerful binary systems. This simulation was developed by NASA.

The ORIGINAL image:

Original Image of Black Hole 10/4/19 13:00UTC

The breakthrough image was captured by the Event Horizon Telescope (EHT), a network of eight radio telescopes spanning locations from Antarctica to Spain and Chile, in an effort involving more than 200 scientists.

Sheperd Doeleman, Event Horizon Telescope Director and Harvard University senior research fellow said: “Black holes are the most mysterious objects in the universe. We have seen what we thought was unseeable. We have taken a picture of a black hole.”

The image gives the first direct glimpse of a black hole’s accretion disk, a fuzzy doughnut-shaped ring of gas and dust that steadily “feeds” the monster within.

A sincere thanks to the above team, for their work .

Source:

https://en.wikipedia.org/wiki/Black_hole

https://en.wikipedia.org/wiki/Black_hole_thermodynamics

https://www.nasa.gov/feature/goddard/2018/new-simulation-sheds-light-on-spiraling-supermassive-black-holes

https://www.nationalgeographic.com/science/space/universe/black-holes/

http://hubblesite.org/reference_desk/faq/answer.php.id=62&cat=exotic

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