Life Cycle of a Star Notes

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University Of Connecticut *

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1025Q

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Astronomy

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Oct 30, 2023

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Life Cycle of a Star Notes ● Stars are created in nebulas, which are superdense regions of space. ● Stars begin to form when areas of a nebula begin to shrink and warm up, due to the gravitational collapse of a molecular cloud. ● This can be caused by galactic collisions, matter being thrown into the nebula at a very high speed by a supernova, or any of several other methods. ● After this happens, the high-pressurized gas and dust will either form a protostar or a brown dwarf. ● In order for a protostar to be formed, massive amounts of gas and dust are needed, having several times the mass of our solar system. Brown dwarfs form when there is not a sufficient amount of mass, and they cannot create hydrogen fusion reactions in their cores, unlike regular stars. ● Protostars exist in the protostar stage for about 100,000 years. Whether or not a star is in this stage is determined by whether material is still falling inward to the star. ● Once protostars stop growing, they become main sequence (“regular”) stars. This stage is the stage in which the star will spend most of its life in. ● To become a main sequence star, a star must be able to fuse hydrogen into helium.

● The mass of a main sequence star can range from a tenth of to 200 times the size of our sun. ● If a star has more mass, it will be able to do more nuclear fusion, but it will have a greater gravitational force and therefore burn faster, giving it a shorter lifetime. ● When a star begins to die out, it will become a Red Giant, and start glowing red due to a change in temperature. ● Red Giants expand rapidly, swallowing up their surroundings (for example, when the sun becomes a red giant, it will most likely expand enough to swallow up the inner planets, and maybe even Earth.) ● After they are done being red giants, stars can transform into a few different stellar phenomena depending upon their size. ● One option for a star’s fate after being a red dwarf is to become a white dwarf. White dwarves only come from small stars, up to 8 times the size of the sun. ● White dwarves are usually only a hundreth the size of our sun but have the same mass, meaning they are very dense. ● In theory, a white dwarf will keep cooling down for about 10 billion years until it becomes a black dwarf. ● Black dwarves would be invisible because their heat signature would equal that of the surrounding universe, so due to this and the fact that the universe is only 13 billion years old, humans have never seen any. ● More massive stars will explode into a supernova. Debris from these giant explosions can reach speeds of 9,000 to 25,000 miles per second.

● Supernovas have created much of the materials that we find on Earth, including the materials in our bodies, such as iron. ● Supernova explosions will leave behind a core, which will turn into either a neutron star or a black hole. ● Neutron stars are similar to white dwarves in that they are both superdense objects; however, a neutron star can be just the size of a city on Earth but weigh 400 tons. They have a “massive” amount of gravity. ● Black holes, on the other hand, are even more dense. In fact, they have infinite density. ● They pull everything around them inside them, and nothing pulled inside can ever escape, not even light. ● Any material object that gets pulled into a black hole will get ripped apart. Specifically, it will get “spaghettified”, which means that its width will be reduced to a miniscule amount and it will become incredibly long, like a spaghetti noodle. ● Black holes, while destructive, can actually be helpful in that they have created many elements due to the fact that they break down matter into subatomic particles. ● A theory exists that objects can escape black holes through objects called “white holes,” but it is disagreed upon where these objects end up, since no one has ever seen a white hole.

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● If a supernova does not become a neutron star or a black hole, then the area of the explosion will slowly cool and form a nebula, which is the area where new stars are born. ● Thus, the life cycle of a star begins again.