why do stars explode when they die
What s going to happen to all the stars in the Universe as they get older? Well, just as nothing can live forever,
stars can t live forever also. Why? Because they run on fuel: burning hydrogen into helium, for example. When they run out of fuel, something s gotta give. reminds us of an excellent and appropriate quote by Do not go gentle into that good night. Rage, rage against the dying of the light. But what exactly happens to the star depends very sensitively on what the mass of the star is. If you ve got a tiny little star, less than about 40% of the mass of our Sun, it burns hydrogen to helium, and doesn t have enough mass to burn helium any further. Our Sun will be able to burn helium into Carbon and Oxygen, and stars significantly more massive will be able to burn Carbon and Oxygen into Neon, Silicon, and even more massive stars will eventually burn those into Iron. Most stars that fall into this category, when they run out of fuel that they re able to burn, will expand into a giant star, and then contract into a white dwarf. White dwarfs don t burn anything, and are only white because they emit light due to the energy released from contracting gravitationally. (For a size comparison, the radius of Earth is 6371 km. ) When they re done shrinking after a few billion more years, they stop emitting light, and become known as black dwarfs. But the most massive stars with iron cores, about 8 times the mass of the Sun or more, go supernova. When they start to contract, the pressure on the iron core becomes so intense that it starts to fuse the protons and electrons found in the iron atoms into neutrons! This causes a tremendous release of energy, known as a supernova explosion: If the star is even more massive, the supernova can become even more powerful, and is known as a. Perhaps, dozens or even a hundred times as massive as our Sun, will go hypernova.
But maybe not! Astronomers from Ireland. They ve been trying to determine what the masses of stars were before they went supernova, by trying to identify which star it was that exploded. Based on their findings, they ve found that some stars may be massive enough that they don t go supernova or hypernova, but instead, when they stop burning their fuel, collapse directly into a black hole! Now this is neat, because in theory it isn t the most massive stars that do this, since their radii will be large enough that they won t directly collapse into black holes, but some special mass range. Here s a diagram I ve found to illustrate the different possible fates of stars, based on their starting mass: Now, what I want to know is, will the, Eta Carinae, the Pistol Star, and LBV 1806-20, go hypernova when they die, or collapse directly to black holes? It might depend on where they are relative to the, but for all we re sure of at this point, it might as well depend on whether they ve read their Dylan Thomas or not! The devastating, explosive deaths of stars appear to be lopsided cosmic conflagrations, scientists say. The new findings, based on data collected by NASA s X-ray mapping, may be a clue into what exactly happens in the hearts of stars as they explode as supernovas, the researchers added. Elements from carbon on upward that make up stars, planets and people are synthesized within massive stars. These elements are spread throughout the universe by the explosions that end the lives of these stars, supernovas that are bright enough to momentarily outshine their entire galaxies. [ Stars that are born with more than about eight times the sun s mass end their lives as so-called core-collapse supernovas. When the core of such a massive star runs out of fuel, it collapses to an extraordinarily dense nugget in a fraction of a second.
Further material falling onto this collapsed core can bounce off it, causing a violent shock wave that blasts matter outward. For decades our best model of supernova explosions forced to collapse symmetrically, said study lead author Brian Grefenstette, an astrophysicist at the California Institute of Technology in Pasadena. Stars are big spherical balls of gas, so it made sense that they should collapse in some kind of spherical way. The problem is that when you try to make a star explode by forcing it to collapse symmetrically, the star doesn t explode, Grefenstette told Space. com. You get a dud. This failure apparently happens in symmetrical models because that shock wave that starts at the center of the star and is supposed to destroy it gets trapped by all of the material above it. This mean the shock wave can t find a way out, Grefenstette said. As such, astrophysicists have explored ways to put ripples in the material of a dying star they call asymmetries that can let the shock wave out and rip apart the star, Grefenstette said. However, it was uncertain how exactly core-collapse supernovas should look the predicted shape could differ significantly depending on which models one used of the explosions. Now scientists have confirmed that by looking at the nearby remnants of such an explosion. Our results are really the first step in being able to see what was going on in the center of the star, Grefenstette said. Researchers investigated, a remnant about 11,000 light-years away of a supernova that happened about 350 years ago. They focused on the distribution of the radioactive titanium isotope Ti-44, which is produced deep in the cores of stars. The supernova tossed out titanium-44 just like a bomb would scatter debris. We re like forensic scientists studying the radioactive ash that the explosion left behind to try to understand what happened during the explosion, Grefenstette said.
Since titanium-44 is radioactive, it glows in a very specific color of light, Grefenstette said high-energy X-rays. The researchers looked at this glowing matter using the NuSTAR space telescope (short for ), which is the first telescope that makes detailed images in this color of light, which lets us unlock a lot of the information that was hidden to us before, Grefenstette said. These images revealed the radioactive isotope was spread around in an uneven manner. This revealed the explosion was more asymmetrical than could be produced by a spherical explosion, although it was not completely lopsided in nature. What our results are pointing toward is the idea that the explosion happens because the core of the star sloshes around a bit during the collapse, Grefenstette said. In this case, we think that what happens is like when you boil water on a stove top, where bubbles are made near the bottom of the pot and rise up, making the surface of the water slosh around and letting some steam escape. In the, the heat, instead of coming from the burner on your stove, is coming from small particles called neutrinos, which are produced in the intense pressure at the center of the explosion, Grefenstette said. These neutrinos heat the material in the center of the collapse and make large bubbles of hot gas that rise up through the material and cause the core of the star to slosh around a bit. This sloshing lets the shock wave escape the material that s holding it back, and once this happens, it s kind of like if you punched a hole in the top of a pressure cooker and the whole thing explodes, Grefenstette said. The scientists detailed their findings in the Feb. 20 issue of the journal Nature. Follow us @Spacedotcom, Facebook and Google+. Original article on.
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