Updated: Jan 11
In this article, we'll try to explain black holes briefly.
The most common way black holes form is from stellar death, when a large star, about 8-10 times the mass of our sun or 8-10 solar masses, reaches the end of its cycle. Inside a star, gravity pulls matter closer together while the nuclear fusion of hydrogen, the star’s fuel, radiates heat and pressure and pushes outward. Once the fuel supply is exhausted, the star implodes causing the outer shell to explode in a supernova.
What happens next depends on the size of the remaining core. If the remaining core of the star is less than 3 solar masses, gravity compresses the electrons and protons forming neutrons. The pressure of neutrons in contact with each other counteracts the force of gravity. The core, now stable and composed primarily of neutrons forms a neutron star.
If the core is greater than 3 solar masses, not even the neutron pressure can counteract the force of gravity and the remaining material will continue to contract and collapse on itself. All of the mass is condensed down into an incredibly small and dense point – White Dwarf...
The white dwarf consists of an exotic stew of helium, carbon, and oxygen nuclei swimming in a sea of highly energetic electrons. The combined pressure of the electrons holds up the white dwarf, preventing further collapse towards an even stranger entity like a neutron star or black hole.
The infant white dwarf is incredibly hot and bathes the surrounding space in a glow of ultraviolet light and X-rays. Some of this radiation is intercepted by the outflows of gas that have left the confines of the now dead star. The gas responds by fluorescing with a rainbow of colors called a planetary nebula. These nebulae – like the Ring Nebula in the constellation Lyra the Harp – give us a peek into our sun’s future
The white dwarf now has before it a long, quiet future. As the trapped heat trickles out, it slowly cools and dims. Eventually it will become an inert lump of carbon and oxygen floating invisibly in space: a black dwarf. But the universe isn’t old enough for any black dwarfs to have formed. The first white dwarfs born in the earliest generations of stars are still, 14 billion years later, cooling off. The coolest white dwarfs we know of, with temperature around 4,000 degrees Celsius (7,000 degrees Fahrenheit), may also be some of the oldest relics in the cosmos.
But not all white dwarfs go quietly into the night. White dwarfs that orbit other stars lead to highly explosive phenomena. The white dwarf starts things off by siphoning gas off its companion. Hydrogen is transferred across a gaseous bridge and spilled onto the white dwarf’s surface. As the hydrogen accumulates, its temperature and density reach a flash point where the entire shell of newly acquired fuel violently fuses releasing a tremendous amount of energy. This flash, called a nova, causes the white dwarf to briefly flare with the brilliance of 50,000 suns and then slowly fade back into obscurity.
What is the event horizon?
The event horizon is the boundary defining the region of space around a black hole from which nothing (not even light) can escape. In other words, the escape velocity for an object within the event horizon exceeds the speed of light.
Sources and references:
The cover photo: https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.istockphoto.com%2Fvideo%2Fblack-hole-gravitational-singularity-moves-across-universe-gm937520232-256435065&psig=AOvVaw0N-w9t2N_Y6LsjuFglbOtm&ust=1610378776294000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCKDbh8nWke4CFQAAAAAdAAAAABAQ