The articles are “Hubble Captures Brilliant Star Death in “Rotten Egg” Nebula” https://www.nasa.gov/image-feature/goddard/2017/hubble-captures-brilliant-star-death-in-rotten-egg-nebula and “The Life and Death of Stars” https://map.gsfc.nasa.gov/universe/rel_stars.html
In these two articles they both explain how different stars die and a recent example of a new star death. NASA who published these articles explains that there are basically two main kinds of stars. Low mass stars that generally fuse hydrogen atoms to make helium atoms at their cores and high mass stars which have carbon cores that contract near the end of its life and fuse different elements to create iron. Both of the stars use fusion to maintain their energy and heat up until their end but go through two different types of cycles. In low mass stars they go through a system called the Proton-Proton cycle.
As shown in the picture above, this is the cycle to which stars with low mass fuse their nuclear energy. Two protons combine together to separate and make one positron and one deuteron to again match up with another proton and create helium 3 and combines with another one of its kind to create a helium 4 then the process starts again. This reaction happens within about a second before it repeats the cycle it’s so fast. A similar cycle happens to high mass stars but just a little bit more complicated. This is called the CNO cycle.
As you can see it functions very closely to the proton-proton cycle but rather than using protons high mass stars have elements like hydrogen, nitrogen, helium, carbon, and oxygen in them. In class we learned that these two cycles have a sort of role in a star’s death in the sense of if the helium gets exhausted out and there is no more fusion cycles happening the star will die out. Just like how there are different cycles for fusion there are different ways a star can die. On one end of star mass there are the small to medium-sized stars. According to the article and what we have learned in class these stars have a relatively laid back death in the cosmic perspective. When a low mass star burns out its life-sustaining gases the core will no longer be able to compete with gravity but the shell around the core will be able to still maintain the heat therefore turning the star into a red giant. When this phase of the star reaches the end the core of the star will collapse under gravity until it reaches a high enough density to start burning helium to carbon. The helium phase will last for a few million years, until the helium in the core has been exhausted and that star then becomes a red supergiant.
(An example to scale of size difference)
This is not the final phase however. Eventually a red giant star will become a white dwarf at the final phase of its life cycle. A white dwarf is the extremely hot core that comes from the left over parts of a star that went through the planetary nebula phase of that star’s death. In my other article from NASA they recently got images from the Hubble Space Telescope of the death of a low mass star in the “Rotten Egg” nebula which is amazing because these events happen in a blink of an eye and are rare to capture. According to scientists in a few thousand years it will become a full planetary nebula.
(The photo from NASA)
(The white dwarf is at the center of the remnants of the planetary nebula phase that came before it)
The other kind of star that was mentioned earlier has two possible ways of dying just dependent upon the mass. High mass stars can either end up becoming a neutron star or a black hole. To become a neutron star, the star’s mass must be at least the mass of 3.0 of our sons. The high mass star cycle to becoming neutron stars includes going from a star with large mass to a red supergiant where the core that is made of carbon contracts even further than a low mass star making it more dense and temperatures high enough to burn carbon to oxygen, neon, silicon, sulfur and finally to iron. Iron the most stable form of nuclear matter, has no energy that can be gained by burning it. After the supergiant stage high mass stars will then com bust into a supernova with the extremely dense and hot core called a pulsar at the middle a lot like the white dwarf of a low mass star. Like the neutron stars, black holes come from the same cycle. A black hole is a spot in space where gravity has so much of an effect that not even light can get out. It is a result where the core of a massive star collapsed and because it became so dense space bends around it and what ever is within the event horizon gets pulled in.
These two articles and this unit, I have to say have been the best so far. The articles helped a lot in better understanding what was taught in this lesson and was just interesting all together. Before this unit I never really knew what a neutron star was. I had heard of them but I had originally thought it was a regular star. Reading these two articles showed that I was wrong in this assumption. I also found it interesting how there are so many stages to how a star dies and that it is different for every star. Everything I learned in this unit I feel will help improve my understanding of the universe and the next units. This was my favorite unit that we have done.