Stellar black holes are very cold: they have a temperature of nearly absolute zero – which is zero Kelvin, or −273.15 degrees Celsius. Super massive black holes are even colder. But a black hole's event horizon is incredibly hot. The gas being pulled rapidly into a black hole can reach millions of degrees. Primordial black holes are thought to have formed in the early universe, soon after the big bang. Stellar black holes form when the center of a very massive star collapses in upon itself. This collapse also causes a supernova, or an exploding star, that blasts part of the star into space. Black holes can be big or small. The smallest black holes are as small as just one atom. These black holes are very tiny but have the mass of a large mountain. Mass is the amount of matter, or "stuff," in an object. Since nothing can escape from the gravitational force of a black hole, it was long thought that black holes are impossible to destroy. But we now know that black holes actually evaporate, slowly returning their energy to the Universe. The defining feature of a black hole is the appearance of an event horizon boundary in space-time through which matter and light can pass only inward towards the mass of the black hole. Nothing, not even light, can escape from inside the event horizon. The black hole at the center of the Perseus galaxy cluster is associated with some sort of sound, NASA said, because there is so much gas in the surrounding galaxy cluster. Astronomers discovered the pressure waves sent out by the black hole were causing ripples in the hot gas. The ultra massive black hole in the galaxy cluster Abell 1201 packs a mass of 30 billion suns. Astronomers have just discovered what may be the largest black hole known to date. The giant black hole has a mass of 30 billion suns and sits at the center of a galaxy located hundreds of millions of light-years from Earth.

Black holes are not hot in the traditional sense because they do not emit light or heat. They are formed from the gravitational collapse of massive stars, which compresses matter to an infinitely small point known as a singularity, surrounded by an event horizon beyond which nothing can escape.

The temperature of a black hole is actually determined by the temperature of the radiation emitted by the matter surrounding it, known as the accretion disk. This radiation can be very hot, but the black hole itself does not have a temperature.

Black holes can come in various sizes, ranging from very small to supermassive. The smallest black holes, known as primordial black holes, could be as small as a single atom but still have the mass of a mountain. On the other hand, supermassive black holes can have masses billions of times that of the sun and are thought to be located at the center of most galaxies, including our own Milky Way.

Rk Naresh,

Dr A. Rehman Jami,

It is by now clear that in practice all galaxies have a supermassive core (black hole). Observations made during the last years show this.

I have in my books (in my profile) described how these cores come about.

When the elementary particles are created out of vacuum through a specific quantum mechanical process, bound pairs of particle-antiparticle are created that form the cores. The binding prevents them from annihilating. It is based on the Heisenberg unscertainty principle. A core is thus build by these bound pairs.

If debris fall in on the cores they may break the bindings and particles will be ejected. The cores will shrink by time which is exactly what recently have been observed. Younger galaxies have larger cores.

i just note that what can escape depends on the mass of the black holes. The debris thrown out have enough energy to escape. Photons do not.

Thanks Dr Hans Gennow and Dr A. Rehman Jami for participating in the discussion.

Black holes are natural phenomena that result from the collapse of very massive stars. They are not hot in the sense that they do not emit heat or light, but they do have a temperature known as the Hawking temperature, which is extremely low for most black holes.

The size of a black hole is typically described by its event horizon, which is the boundary around the black hole beyond which nothing, not even light, can escape. The size of the event horizon is determined by the mass of the black hole. For example, a black hole with a mass similar to our sun would have an event horizon with a radius of about 3 kilometers (1.9 miles), while a supermassive black hole at the center of a galaxy could have an event horizon with a radius of several billion kilometers.

I agree with Dr Hans Gennow that every large galaxy contains a super massive black hole at its center. The super massive 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 very large ball that could hold a few million Earths. Primordial black holes are thought to have formed in the early universe, soon after the big bang. Stellar black holes form when the center of a very massive star collapses in upon itself. This collapse also causes a supernova, or an exploding star, that blasts part of the star into space. A typical stellar-class of black hole has a mass between about 3 and 10 solar masses. Super massive black holes exist in the center of most galaxies, including our own Milky Way Galaxy. They are astonishingly heavy, with masses ranging from millions to billions of solar masses. The largest black hole ever found in the known universe is found in Ton 618. This is a hyper luminous Lyman-alpha blob that has a black hole that measures 6.6×1010 solar masses. It has a mass that equals about 66 billion times that of the Sun. This super massive black hole is some 18.2 billion light-years from Earth. Hot Stuff! When gas flows into a black hole, it gets very hot and emits light. The gas is heated because the atoms collide with each other as they fall into the black hole. Stellar black holes are very cold: they have a temperature of nearly absolute zero – which is zero Kelvin, or −273.15 degrees Celsius. Super massive black holes are even colder. But a black hole's event horizon is incredibly hot. The gas being pulled rapidly into a black hole can reach millions of degrees.

“…Black holes are natural phen omena that result from the collapse of very massive stars. They are not hot in the sense that they do not emit heat or light, ….”

- from that something don’t radiate, heat or light, if we don’t mention “something is hot “since if we touch it, then the finger feels heat”, by no means it follows that this something is cold - tea in a thermos can be hot while the thermos is cold.

But if we tell about some matter independently on it is in a thermos or not, that the quote above also isn’t a correct answer to the question - are black holes hot?

Really “black holes”, not, of course, the “GR black holes” which are some “holes in spacetime” , are compact and extremely dense material objects, where matter is in “fourth” phase state - after “ordinary matter”, “white dwarf”, and “neutron star” phase states

BHs are indeed extremely exotic physical objects, including have some surfaces in 3D space where the escape velocity formally is equal to the speed of light, in the GR radius of such “event horizon surface” is defined as the Schwarzschild radius, RS, in Newton Gravity law the radius of this surface is two times lesser than RS,

- however that by no means implies that on this surface particles’, bodies’, etc., if they fall into a BH becomes be equal to zero, and so the energy of these particles, bodies, etc. becomes to be infinite - that evidently is prohibited by energy conservation law, what really – in contrast to the GR and Newton mechanics happens in this case in a first approximation is considered in the Shevchenko-Tokarevsky’s 2007 initial model of Gravity [and Electric] Forces, see

https://www.researchgate.net/publication/365437307_The_informational_model_-_Gravity_and_Electric_Forces

What is this matter’s “back hole phase state” is practically unknown now, nonetheless it looks as quite reasonable to suggest that the BHs are composed from some particles, and these particles aren’t “frozen” as some crystal – something like the case when a nucleus of an atom can be cooled to practically zero temperature, but nucleons in it move with rather large speeds having well essential energies, and so if someone would push a finger into the nucleus, it would feel heat, while at that nucleus isn’t in a thermos;

- and the matter in BH phase state, which also isn’t in a thermos, is well hot as well.

More about what are “black holes” besides the link above see the section “Cosmology” in https://www.researchgate.net/publication/355361749_The_informational_physical_model_and_fundamental_problems_in_physics

Cheers

Thanks Dr. Sergey shevchenko for participating in the discussion.

The more massive a black hole, the colder it is. Stellar black holes are very cold: they have a temperature of nearly absolute zero – which is zero Kelvin, or −273.15 degrees Celsius. Super massive black holes are even colder. The most massive black holes in the Universe, the super massive black holes with millions of times the mass 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. Stellar black holes are very cold: they have a temperature of nearly absolute zero – which is zero Kelvin, or −273.15 degrees Celsius. Super massive black holes are even colder. But a black hole's event horizon is incredibly hot. The gas being pulled rapidly into a black hole can reach millions of degrees. They're some of the most violent objects in our universe, powerful enough to rip entire stars to pieces. Their secret weapon is gravity. You see the more mass you can shrink into a small space, the stronger your gravitational force will become. Peppered throughout the Universe, these "stellar mass" black holes are generally 10 to 24 times as massive as the Sun. Astronomers spot them when another star draws near enough for some of the matter surrounding it to be snared by the black hole's gravity, churning out x-rays in the process. Is it possible for a black hole to "eat" an entire galaxy? No. There is no way a black hole would eat an entire galaxy. The gravitational reach of super massive black holes contained in the middle of galaxies is large, but not nearly large enough for eating the whole galaxy.

Rk Naresh,

the supermassive objects in the center of the galaxies (galaxy core) are about a factor 1000 less massive the the galaxies them selves. This is what I have arrived to and it fits very well with recent observations (see my last book).

The effect of the core on e.g. the velocity distribution in the galaxy is demonstrated in my first book. The effect is much too small to affect the galaxy.

Thanks Dr. Hans Gennow for participating in the discussion.

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Rk Naresh,

I now have noted that you wonder about the size of the supermassive objects. I can tell you that from my simulation an average core of 10^37 kg have a radius of 3 times that of the sun.

I also want to note that these cores are produced within about 20 minutes from the bang. After creation they start to accrete debris and build the galaxy halo but it takes some milion years. So, the cores creates galaxies, not eat them. As I mentioned my results fit very well with present observations.