A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space.
In around 4.5 billion years the sun will
run out of hydrogen in its core meaning it can no longer sustain nuclear fusion. This will signal the end of the outward pressure that stops its core from collapsing under gravity.
As the core collapses, the outer
layers of the sun will puff out in a series of outbursts beginning a short-lived
red giant phase for our star. In the core helium created by the fusion of hydrogen will begin to fuse into carbon.
The shed outer layers will spread out to the orbit of
Mars, consuming the inner planets including
Earth, eventually becoming a planetary nebula that surrounds a scorching hot, albeit gradually cooling stellar core known as a white dwarf.
This is how our sun and other low to medium mass stars will remain for trillions of years, meaning the sun will not explode.
This isn’t the end for all stars, however. Some have enough mass to push past this white dwarf phase and initiate further nuclear fusion, a supernova, and the transformation into an exotic stellar remanent.
The dividing line between these fates is the Chandrasekhar limit.
The most well-understood
black holes are created when a massive star reaches the end of its life and implodes, collapsing in on itself.
Chandrasekhar limit, in astrophysics, equates to the maximum mass theoretically possible for a stable
white dwarf star.
This limiting value was named for the Indian-born astrophysicist
Subrahmanyan Chandrasekhar, who formulated it in 1930. Using
Albert Einstein’s special theory of relativity and the principles of
quantum physics, Chandrasekhar showed that it is impossible for a white dwarf star, which is supported solely by a
degenerate gas of electrons, to be stable if its mass is greater than 1.44 times the mass of the
Sun. If such a
star does not completely exhaust its thermonuclear fuel, then this limiting mass may be slightly larger.
All direct mass determinations of actual white dwarf stars have resulted in masses less than the Chandrasekhar limit. A star that ends its nuclear-burning lifetime with a mass greater than the Chandrasekhar limit must become either a
neutron star or a
black hole.
In stellar cores with a mass greater than 1.44 times that of the sun, carbon burning can be initiated creating neon. This leads to further stages of core contraction and the burning of successively heavier elements until the heaviest element that can be synthesized in stars , iron, fills the core.
With no more fusion possible, the stellar core collapses one final time. If the core has a mass under 3 times that of the sun, neutron pressure protects it from complete collapse leading to the creation of a neutron star. This is the densest state of matter equivalent to a star the size of the sun squashed into the radius of a city.
For stellar remnants over 3 solar masses, predicted to have begun as
stars with 10 to 24 times the mass of the sun, complete collapse occurs leading to the final stage as a black hole.
Exceeding the Chandrasekhar limit doesn’t just create some of the most fascinating and mysterious cosmic objects in black holes and neutron stars, but the supernova that signals their birth is a vital part of the evolution of
the universe.
This is because these cosmic explosions take heavy elements synthesized during the lifetime of the massive stars and spread them across the cosmos. This provides the building blocks that form the next generation of stars and their planets and which provided the elements necessary for life here.
Eventually, by growing and consuming material — planets, stars, errant spaceships, other black holes — astronomers think they evolve into the supermassive black holes that they detect at the centers of most major galaxies.
There’s very little direct evidence of so-called intermediate-mass black holes — the ones in between star-sized and galaxy-sized. Astronomers expect to see some black holes in this middle phase, on their way to
becoming supermassive but not quite there yet — and, so far, they mostly don’t.
Both tiny and enormous black holes do exist. We’re just still connecting the dots between them.
With all the hydrogen of a stellar core exhausted at the end of the main sequence the white dwarf that remains consists mainly of carbon — created by the fusion of helium in the red giant stage.
A white dwarf with a mass of 1.4 solar masses or less can’t initiate carbon burning but continues to contract until this is halted by
electron degeneracy pressure.(opens in new tab)
This is the principle from quantum physics that prevents two electrons from occupying the same quantum state and essentially preve
A black hole takes up zero space, but does have mass — originally, most of the mass that used to be a star. And a black hole gets more massive as it consumes matter nearby. The bigger they are, the larger a zone of “no return” they have, where anything entering their territory is irrevocably lost to the black hole. This point of no return is called the event horizon.
Because no light can't escape due to the enormous gravity of the central mass, people can't see black holes. They are invisible. Space telescopes with special tools can help find black holes. The special tools can see how stars that are very close to black holes act differently than other stars by circling a central gravimetric point at high speed.
Black holes can be big or small. Scientists think 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.
Another kind of black hole is called "stellar." Its mass can be up to 20 times more than the mass of the sun. There may be many, many stellar mass black holes in Earth's galaxy. Earth's galaxy is called the Milky Way.
The largest black holes are called "supermassive." These black holes have masses that are more than 1 million suns together. Scientists have found proof 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 very large ball that could hold a few million Earths.
Stellar black holes are made when the center of a very big star falls in upon itself, or collapses. When this happens, it causes a supernova. A supernova is an exploding star that blasts part of the star into space and can be brighter than its host galaxy for a period of time, varying with the total mass within it.
Scientists think supermassive black holes were made at the same time as the galaxy they are in.
A black hole can not be seen because strong gravity pulls all of the light into the middle of the black hole. But scientists can see how the strong gravity affects the stars and gas around the black hole. Scientists can study stars to find out if they are flying around, or orbiting, a black hole.
Black holes are among the most mysterious cosmic objects, much studied but not fully understood. These objects aren’t really holes. They’re huge concentrations of matter packed into very tiny spaces. A black hole is so dense that gravity just beneath its surface, the event horizon, is strong enough that nothing – not even light – can escape. The event horizon isn’t a surface like Earth’s or even the Sun’s. It’s a boundary that contains all the matter that makes up the black hole.
When a black hole and a star are close together, high-energy or ultra-violet light is made. This kind of light can not be seen with human eyes. Scientists use satellites and telescopes in space to see the ultra-violet light.
Black holes do not go around in space eating stars, moons and planets. Earth will not fall into a black hole because no black hole is close enough to the solar system for Earth to do that.
Even if a black hole the same mass as the sun were to take the place of the sun, Earth still would not fall in. The black hole would have the same gravity as the sun. Earth and the other planets would orbit the black hole as they orbit the sun now.
The sun will never turn into a black hole. The sun is not a big enough star to make a black hole.
Black holes don’t emit or reflect light, making them effectively invisible to telescopes. Scientists primarily detect and study them based on how they affect their surroundings:
- Black holes can be surrounded by rings of gas and dust, called accretion disks, that emit light across many wavelengths, including X-rays.
- A supermassive black hole’s intense gravity can cause stars to orbit around it in a particular way. Astronomers tracked the orbits of several stars near the center of the Milky Way to prove it houses a supermassive black hole, a discovery that won the 2020 Nobel Prize for Andrea Ghez of UCLA* and her colleagues.
- When very massive objects accelerate through space, they create ripples in the fabric of space-time called gravitational waves. Scientists can detect some of these by the ripples’ effect on detectors.
- Massive objects like black holes can bend and distort light from more distant objects. This effect, called gravitational lensing, can be used to find isolated black holes that are otherwise invisible.
* Andrea Ghez - In May of 2022, the world got
its first-ever look at Sagittarius A*, the supermassive black hole residing in the center of our Milky Way galaxy. The image of a hazy golden ring of superheated gas and bending light was captured by
the Event Horizon Telescope, a network of eight radio observatories scattered across the globe.
Feryal Özel, a University of Arizona astronomer and founding member of the EHT consortium, said that seeing the black hole’s image was like finally meeting in real life a person you’ve only interacted with online.
For
Andrea Ghez, an astrophysicist at UCLA, the encounter was perhaps more like a biographer meeting her subject after decades of pursuit.
See:
https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html
See:
https://astronomy.com/news/2020/02/how-do-black-holes-form
See:
https://www.britannica.com/science/dwarf-star
The foregoing should give you a better idea about black holes, the size of their parent stars, and the result of the various types of stellar gravitational collapse vis a vis size.
Black holes are points in space that are so dense they create deep gravity wells or sinks. Beyond a certain region, known as the event horizon, 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.
In astrophysics, spaghettification is the tidal effect caused by strong gravitational fields. When falling towards a black hole, for example, an object is stretched in the direction of the black hole (and compressed perpendicular to it as it falls). In effect, the object can be distorted into a long, thin version of its undistorted shape, as though being stretched like spaghetti.
The curved line in the diagram represents a section of the surface of the black hole. In the left hand drawing, the astronaut’s height and width correspond as expected. As they move closer to the centre of the black hole, they experience slight compression horizontally and elongation vertically. In the right hand image, they are closer still and the compression and elongation of their form are even more dramatic.
Spaghettification is not inevitable. Black holes of different masses will have different gradients, so with supermassive black holes it is perfectly possible to pass the event horizon with no ill-effect. Again, this is not to say that the gravitational pull isn’t strong, just that the gradient isn’t too extreme. Let’s assume this is the case.
Unfortunately, other stuff seems to be falling into our black hole too.
Although a bit of company might seem welcome, infalling particles spiral into the black hole in a turbulent flow, rubbing up against each other. As we’ve seen, the accretion disc circling a black hole emits radiation due to this friction and, because of the immensity of the gravitational pull, particles are accelerated up to significant fractions of the speed of light.
The result is highly energetic radiation, like powerful x-rays. The black hole may even produce tightly focused astrophysical jets of ionised matter (sufficiently powerful and with velocities high enough to be referred to as relativistic jets which approach the speed of light).
Jets of super heated matter may extend millions of light years. They’re also complicated with numerous unanswered questions surrounding them. Significantly, they align with the axis of rotation, whereas inflating matter is approaching almost perpendicular to it in the accretion disc.
There are
four types of black holes: stellar, intermediate, supermassive, and miniature. The most commonly known way a black hole forms is by stellar death. As stars reach the ends of their lives, most will inflate, lose mass, and then cool to form
white dwarfs. But the largest of these fiery bodies, those at least 10 to 20 times as massive as our own sun, are destined to become either super-dense
neutron stars or so-called stellar-mass black holes.
Hartmann352