Most black holes form from the remnants of a large star that dies in a supernova explosion. (Smaller stars become dense neutron stars, which are not massive enough to trap light.)
A black star is a gravitational object composed of matter. It is a theoretical alternative to the black hole concept from general relativity. The theoretical construct was created through the use of semiclassical gravity theory.
A black hole IS compressed by gravity in the extreme to such an extent that it is neither formed by gases anymore nor produce nuclear fusion. It also does not produce light and it's only output is Hawking Radiation, so, once it collapses in on itself, it does not conform to the definition of a star any longer.
Black holes have two parts. There is the event horizon, which you can think of as the surface, though it's simply the point where the gravity gets too strong for anything to escape. And then, at the center, is the singularity. That's the word we use to describe a point that is infinitely small and infinitely dense.
Rather, it emits a combination of all the radiation from all the objects that ever fell into it (which will asymptote to, but never reach, zero) along with the ultra-low-temperature but always-present Hawking radiation. You might have thought that black holes truly are black, but they aren't.
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.
At the center of a black hole the gravity is so strong that, according to general relativity, space-time becomes so extremely curved that ultimately the curvature becomes infinite. This results in space-time having a jagged edge, beyond which physics no longer exists -- the singularity.
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.
Near a black hole, the slowing of time is extreme. From the viewpoint of an observer outside the black hole, time stops. For example, an object falling into the hole would appear frozen in time at the edge of the hole.
Over time they shrink down to nothing and simply pop away in a flash of energy. It's not exactly fast. A good size black hole — say, a few times more massive than the sun — will take about 10^100 years to eventually evaporate through this process, known as Hawking Radiation.
Black holes can act as engines of creation or re-creation, if you will—helping form galaxies, stars and planets in a rebounding galaxy. “Maybe the black holes are one of the reasons why the universe is capable of bouncing back after one of its once-every-30-billion-years-or-so contractions.”
When stars die, they become either black holes, neutron stars, or white dwarfs.
Anything outside this surface —including astronauts, rockets, or light—can escape from the black hole. But once this surface is crossed, nothing can escape, regardless of its speed, because of the strong gravitational pull toward the center of the black hole.
The Sun would need to be about 20 times more massive to end its life as a black hole. Stars that are born this size or larger can explode into a supernova at the end of their lifetimes before collapsing back into a black hole, an object with a gravitational pull so strong that nothing, not even light, can escape.
In fact, the possibility of creating a black hole in a lab is a goal that scientists are actively pursuing—one that could allow researchers to answer many fundamental questions about quantum mechanics and the nature of gravity. A black hole typically forms when a star much more massive than our sun dies.
Roughly one out of every thousand stars that form is massive enough to become a black hole. Therefore, our galaxy must harbor some 100 million stellar-mass black holes. Most of these are invisible to us, and only about a dozen have been identified.
on edge of Black Hole. Space and time are intertwined, called space-time, and gravity has the ability to stretch space-time. Objects with a large mass will be able to stretch space-time to the point where our perception of it changes, known as time dilation.
Einstein's theory of general relativity mathematically predicts the existence of wormholes, but none have been discovered to date. A negative mass wormhole might be spotted by the way its gravity affects light that passes by.
Even if we see the universe from a point very close to the apparent event horizon, the time dilates to such an extent that the time of the locations away from tne universe will be much faster (say 1 second for the observer near blak hole will be 100000 years for an observer on earth).
It is possible for two black holes to collide. Once they come so close that they cannot escape each other's gravity, they will merge to become one bigger black hole. Such an event would be extremely violent.
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 supermassive black holes contained in the middle of galaxies is large, but not nearly large enough for eating the whole galaxy.
Astronomers have discovered two new black holes that are the closest ones to Earth known, and also represent something that astronomers have never seen before. The black holes, designated Gaia BH1 and Gaia BH2, were discovered in data collected by the European Space Agency's (ESA) Gaia spacecraft.
Well, even though black holes are extreme in many ways, they don't have infinite mass—and it's mass that determines the force of their gravity.
According to a mind-bending new theory, a black hole is actually a tunnel between universes—a type of wormhole. The matter the black hole attracts doesn't collapse into a single point, as has been predicted, but rather gushes out a "white hole" at the other end of the black one, the theory goes.
The person would experience spaghettification, and most likely not survive being stretched into a long, thin noodlelike shape.