Written by Youngwoo Chang
Editor’s note: We have been centered on AI and its possibilities in our research topics, however, we have wanted to present an article on astronomy as it is a fascinating topic. This article will be on Neutron stars, and our next article (which will be featured in the journal) on astronomy will be about black holes. As we are nearing the official month of presenting our first journal, we have been wanting to show our readers an article which is similar to a prequel to the second astronomy article. We hope you enjoy our article. Neutron stars are the remainders of a supernova of a star that had a mass of eight to twenty solar mass. The eight to twenty solar mass star explodes into a supernova, and matter and plasma are blasted out just at a fraction of the speed of light. The small ball (about two dozen kilometers in diameter) consisting of neutrons remain at the center. A neutron star is born. When stars are born, they fuse hydrogen and form helium. This is the main source of fuel for stars. Our sun, an average sized star, can fuse hydrogen for about 10 billion years. Average sized stars can only fuse until carbon. Our sun will fuse elements until it reaches carbon. Then, it will stop fusing and collapse into a white dwarf. However, more massive stars (more than 8 times the sun’s mass) can fuse elements past carbon. You may think that massive stars have a longer lifespan, but massive stars burn through their fuel much faster so they have a shorter lifespan. How do stars function? Stars, at first, fuse hydrogen. When hydrogen is used up, the star expands but the core shrinks because of gravity. Our sun will expand to a red giant but more massive stars exert a lot of energy and expand to a red supergiant. When this occurs, helium fusion starts and forms carbon. The star shrinks and expands constantly as the core goes on from one fusion to the next fusion. Generally, fusing heavier elements need a higher temperature and pressure. When the stars’ temperature climbs up to 5,000,000ºC, carbon starts to fuse. It fuses with helium to form oxygen and fuses with other elements to form magnesium and sodium. These elements accumulate and the star’s core temperature goes up and those elements fuse to form heavier elements. Eventually, you get multiple layers in the sun. The outer layer consists of hydrogen, helium, and nitrogen; the second outermost of oxygen, neon, and magnesium; the final layer of silicon, sulfur; and you have iron and some nickel as a result of silicon fusion towards the latter steps of fusion. As iron is fused, the death of the star comes closer and closer. When the core starts fusing iron, iron absorbs energy instead of releasing it. The core loses the support to maintain the tremendous gravity. As soon as iron fusion happens, the collapsing of the star begins. As the core collapses, the temperatures continue to rise. In addition, the electrons get absorbed by the nucleus of the iron which also one of the factors that support the core. As a result, the star collapses to about a dozen or two kilometers in a fraction of a second. In stars which are not so massive, the pressure from electrons that resist being held too tight allows the core to prevent further collapse. For a star that has a core that is greater than 1.4 solar mass, the force of the collapse is greater than the electron degeneracy pressure and collapses further. The protons and electrons collide into the same space and form neutrons. Another pressure where neutrons resist being held too tight finally stop the collapse. The neutrons become in place and the collapse is stopped; then, the force reverses direction and goes out. A huge amount of energy is released along with neutrinos and a supernova happens. In the center of the supernova, a neutron star is formed. A neutron star has a diameter of about 20km with an escape velocity up to half the speed of light. They have a very high density, a teaspoon of a neutron star will have a mass of millions of tons. The reason for this is because the neutrons are tightly packed together. An atom is mostly composed of empty space, but this isn’t the case for neutron stars. All of that void will be filled with neutrons. Pulsars are neutron stars that have a swift rotation with an immensely strong magnetic field and have jet-like beams that shoot out energy from the star. From Earth, this can be observed as a sudden increase in brightness. Since the orbit of neutron stars are very stable, the ‘bleep’ happens very regularly. Not only do these jets release visible light, but it also releases radio waves and X-rays. When the scientists first observed this, they thought it was a signal sent by an alien. There are many characteristics of neutron stars. Neutrons stars spin very fast because when stars shrink, the rate of spin increases. Some neutron stars spin so fast that they have a rotational period of 1-10 milliseconds which called millisecond pulsars. Also, neutron stars have very, very strong magnetic field. It is so strong that the magnetic field is 1,000,000,000,000 Gauss and is about a trillion times stronger than our sun’s magnetic field. Some neutron stars, about 10% of them, have abnormally strong magnetic fields; about a quadrillion gauss. This is incredibly strong because a bar magnet is just about a 100 gauss. These neutron stars are called magnetars. One of the most fascinating things of magnetars is starquakes. The crust and magnetic field work together so if there is a sudden shift in the crust, there are devastating consequences. Since neutron stars are incredibly dense, even if just a tiny, tiny crack, say like a few inches, the energy from the crack is so great that the energy is released by an explosion. The largest starquake recorded was back in 2004, by a neutron star, SGR-1806-20. This neutron star was 50,000 light years away and its effects were felt on Earth. Since magnetars are very rare and far away, future starquakes and disasters aren’t a problem for us. A rising question such as ‘What if the star has a mass of more than 20 solar mass and the core collapsed?’ will lead to another matter which is commonly discussed in astronomy. The core of the star will collapse and will overcome the electron degeneracy and neutron degeneracy pressure. Consequently, the core cannot be stopped by any other force and becomes one of the most bizarre objects in the universe: a black hole. SOURCES:
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