Destination: Black Hole

I like black holes. I like them a lot. They are in the top ten of my bucket list of destinations if I live for a thousand years.

Seems Legit

Seems Legit

Black holes in popular culture are notorious for being very dark objects. I will try enlighten the readers about their shady origins, and hope that people see them in a better light.

Stars run on hydrogen. In the extreme temperatures in their cores, hydrogen nuclei fuse explosively to form helium nuclei. The explosive energy released opposes the force of gravity of the star on itself. Thus the star continues its merry existence, until it runs out of juice, that is. When there is no more hydrogen left to fuse, the temperature at the core decreases, gravity takes over and the star contracts. The contraction again heats up the core to a level where helium fuses into carbon. This reaction is much more powerful than hydrogen fusion, and the explosive output causes the star’s shell to expand, making it a red giant.

If the star is less that 10.5 solar masses then it sheds its outer layers leaving behind a very dense white dwarf star made of oxygen and carbon. the white dwarf star is prevented from collapsing further by the electron degeneracy pressure. However, if the mass of the white dwarf is more than about 1.4 times the mass of the sun, even electron pressure cannot hold back gravity. And so the electrons fuse with protons to become neutrons, thus forming a neutron star. A neutron star achieves stability due to the quantum degeneracy pressure (that particles simply cannot have the same state and so must remain separate).

However, if the mass of the neutron star exceeds 1.5 to 3 solar masses, it collapses again into one of several exotic remnants, one of which is the black hole.

starlife

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7 thoughts on “Destination: Black Hole

  1. I have also been very interested in black holes. Your description of how they are formed was very helpful in understanding where they come from as well as the diagram. I did not know that the path of a star could lead to a red supergiant, the supernova, then possibly turn into a black hole. Pretty cool stuff!

  2. I really like the diagram you used for the life cycle of stars, as well as your explanation of degeneracy pressures. It’s pretty amazing to me that just these degeneracy pressures are able to prevent some stars from collapsing due to gravity. Black holes and their properties are also pretty amazing. Very interesting

  3. Nice! I definitely needed a refresher on star life cycles since I took Intro Astronomy a few years ago. I like that you included the actual masses at which stars will become either a white dwarf, neutron star, or black hole. I wonder if those thresholds are exact and what would happen to a star with a mass that is exactly on the threshold.

    • The thresholds have not been defined with absolute precision. Moreover there is no “exact” mass due to quantum uncertainty. All we can do is to specify bands where the magic happens up to a high degree of accuracy.

  4. Black holes are a very cool topic and you did a nice job of explaining them. I wasn’t really clear on the formation of neutron stars so your diagram and explanation of that was really helpful. That said, I don’t think that diagram is 100% complete. If I recall correctly, white dwarves can actually become supernovas.

    • Yes, they are called type 1a supernovas. They happen when the white dwarf is more than ~1.4 times the mass of the Sun. The gravitational forces are so high that they force the white dwarf to contract. the contraction increases temperatures to levels where Carbon and Oxygen fuse to form heavier elements. However this reaction is so explosive that the white dwarf rebounds and explodes in a supernova (which is a very big explosion). Sometimes the rebound is so strong that the core (according to newton’s 3rd law) compresses to fuse electrons and neutrons, thus becoming a neutron star.

  5. Pingback: Trous Noirs And trous noirs | Astronomy 201

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