4. Understanding Black Hole

After having gone through Neutron Star, Supernova and Basics of Black Hole; now we leap towards Understanding Black Hole.

Understanding Black Hole as Pothole

Astrophysicist believe that the entire universe is a Four Dimensional Sheet and every piece of matter in the universe causes a little pothole. More massive an object, the deeper the pothole, deeper the dent in this sheet. We are all living on the sheet, so there’s nothing above there’s nothing below so we are all confined. All celestial bodies are confined to move in this sheet and the sheet is expanding all the time.

Understanding Black Hole; It’s a complex kind of interrelationship between the shape motions and matter so if you look at how the mass of an object determine the shape and depth of the pothole it creates but how mass is packed in it.

The density matters like the sun would cause a nice big pothole. Then if you have a neutron star, it’s much denser than the sun so it’s going to have a deeper pothole and a black hole is going to cause a puncture in space-time.

Inside the Black Hole

Products of Einstein’s equations are as almost like mathematical entities being the end states of massive stars. They are seen as punctures in space-time. If you compress the entire earth for instance into a black hole now that would be an awfully small black hole. Once the event horizon is crossed, something bizarre happens, because no light, nothing can escape.

In terms of Understanding Black Hole; it is not known what happens to objects that actually cross the event horizon of a black hole but we have some ideas but what we don’t know is what happens to the information. What is their mass, what if someone fall into the black hole, there would be nothing; would know nothing. This is a big unsolved problem hence the peculiar nature of the event horizon.

Properties of Black Hole

Light is our cosmic messenger. All information in the universe is transmitted through light

We obtain that through light or some other kinds of waves like gravitational waves. If we talk about the fundamental properties of a black hole they are basically three properties to fully define a black hole. They are mass, spin (whether it’s spinning or not) and charge.

For most astrophysical black holes, charge is not really a relevant quantity; it is mass and spin and that is what really being followed astrophysics. Astrophysicists are trying Understanding Black Hole to measure masses and spins because the measurements of masses and spins helped us on our theoretical understanding of how black holes grow and test our models.

Analogy to Loss of Information

That’s kind of abhorrent to Albert Einstein Total Loss of Information. There’s a beautiful analogy Stephen hawking presented on loss of information. He said that it’s like having an encyclopedia Britannica and you actually put the Encyclopedia Britannica in a box, in a really tight box; from which nothing can escape. Now burn it down completely, burn it down till every particle of ash inside that box. Nothing’s left that box right so the information that was in the Encyclopedia Britannic is still in there.

It’s just no longer stored in the form of pages and printed ink and so on. We no longer know the act of reading like of actually accessing the information. The information is clearly there but it is in some form perhaps that is we cannot recover and we don’t even know how it’s stored.

This is the best that you know the best analogy. The information is likely there, we just don’t know quite how to retrieve it so we’re not completely losing. There are some of the most massive black holes in the universe like the one in the center of our own galaxy, can be either Fasting or Feasting like the one in the center of the milky way; the supermassive one four million times the mass of the sun.

We typically see black holes is when matter is swirling in and it’s being pulled in by the gravity of black hole gas. Typically it gets heated; hotter and hotter as it’s getting closer and closer to the event horizon; starts to glow and it glows in the X-Rays. That’s how we see most commonly feasting supermassive black holes.

Witnessing a Black Hole

Once it has a have little feeding episodes. So if you have a stellar mass black hole that is next to a star that strays close or it’s bound to another star. It could start feeding slowly ripping the star apart and start feeding. Once again that gas as it falls in so you always see sort of these dying gasps of gas around black holes.

For the black holes like the one in the Milky Way, we actually see them in a completely different way. They are not feasting so what they do; they control the motions of the stars that are right nearby. It’s like the solar system; we see the planets on elliptical orbits and the sun is one of the foci and you know the most massive object in the solar system is the sun.

Similarly the black hole is really sitting right there and we are able to measure the mass of the black hole by looking at orbits. It turns out that almost all the black holes supermassive ones nearby are fasting. This is the way to detect them but then this method doesn’t work for black holes that are far away because to resolve all the stars you’ve got to map motion of every star and that’s incredibly hard.

The centers of galaxies are incredibly bright. They’re chock-a-block filled with stars. So astrophysicist can’t resolve them till huge telescopes; so next generation telescopes will allow us to go even further out than we have to detect these fasting black holes. But it’s the feasting ones supermassive ones that we detect much more easily because of X-ray emission.

The dramatic new way in which we started detecting black holes recently was when two black holes collide and we have detected the collision of two stellar mass black holes.

Categories

Astrophysicists categorize Black Holes in mass as in Slim Small Stellar Mass Black Holes; the end states of stars. Intermediate Mass Black Holes that are about a thousand to ten thousand; forty fifty thousand times the mass of the sun. Super Massive are black holes that are Million to a Billion Solar Masses. The Obese Ones; the Ultra Massive black holes that are more massive than billions of solar masses

This looks kind of arbitrary, actually it’s not arbitrary. The way they have been classified because different ways of being born. So Stellar Mass Black Holes born of stars. The question of course for next generation is “can you start from these stellar mass black holes, feed them and make them Intermediate Mass Black Holes and then Supermassive Black Holes and Ultra Massive Black Holes?”

Genesis

Black holes didn’t have to come from stars because so early in the universe stars did not exist. It was probably these Direct Collapse Black Holes. These are basically when you have a lot of gas in the early universe and  it settles down into kind of a disk in the center of a galaxy; no stars have formed yet in this particular galaxy. The gas siphons in because of an instability.

Taking a thought experiment; It is like you’re sitting in bathtub and pull the plug and see that vortex of water going in really fast. That kind of pulling the plug instability equivalent of that loosely speaking happens in the very early universe can happen and siphon a lot of matter down very fast because that’s what you need to make a black hole.

A lot of matter must have been down rapidly and this is believed to happen simultaneously when the first stars form in the early universe. That is one way to make Intermediate Mass Black Holes; a thousand to 10 to five times the mass of the sun. Very early in the universe and of course from those; build up the Super Massive Black Holes. From these direct Collapse Black Holes; that are Intermediate Mass Black Holes, in the very early universe can build up very rapidly to actually make very Supermassive Black Holes.

The reason you want to make them early is because you’re seeing these feasting black holes which are called Quasars out to the largest distances at the earliest times in the universe so there’s like a timing crunch. If one start with a Stellar Mass Seed; have to like overfeed it and that’s kind of challenging. If the black holes start off with a seed that’s already intermediate mass then it’s very easy to account for the Supermassive Black Holes.