 There are a few places in the universe that defy comprehension. And supernovae have got to be the most extreme places you can imagine. We're talking about a star with potentially dozens of times the size and mass of our own sun that violently dies in a faction of a second. Faster than it take me to say the word supernova, a complete star collapses in on itself, creating a black hole, forming the denser elements in the universe, and then exploding outward with the energy of millions or even billions of stars. But not in all cases. In fact, supernovae come in different flavours, starting from different kinds of stars, ending up with different kinds of explosions, and producing different kinds of remnants. There are two main types of supernovae, the Type I and the Type II. I know this sounds a little counter intuitive, but let's start with the Type II first. These are the supernovae produced when massive stars die. We've done a whole show about that process, so if you want to watch it now, you can click here. But here's the shorter version. Stars, as you know, convert hydrogen into fusion at their core. This reaction releases energy in the form of photons, and this light pressure pushes against the force of gravity trying to pull the star in on itself. Our sun, doesn't have the mass to support fusion reactions with elements beyond hydrogen or helium. So once all the helium is used up, the fusion reactions stop and the sun becomes a white dwarf and starts cooling down. But if you have a star with 8-25 times the mass of the sun, it can fuse heavier elements at its core. When it runs out of hydrogen, it switches to helium, and then carbon, neon, etc, all the way up the periodic table of elements. When it reaches iron, however, the fusion reaction takes more energy than it produces. The outer layers of the star collapses inward in a fraction of a second, and then detonates as a Type II supernova. You're left with an incredibly dense neutron star as a remnant. But if the original star had more than about 25 times the mass of the sun, the same core collapse happens. But the force of the material falling inward collapses the core into a black hole.
Extremely massive stars with more than 100 times the mass of the sun just explode without a trace. In fact, shortly after the Big Bang, there were stars with hundreds, and maybe even thousands of times the mass of the sun made of pure hydrogen and helium. These monsters would have lived very short lives, detonating with an incomprehensible amount of energy. Those are Type II. Type I are a little rarer, and are created when you have a very strange binary star situation. One star in the pair is a white dwarf, the long dead remnant of a main sequence star like our sun. The companion can be any other type of star, like a red giant, main sequence star, or even another white dwarf.
What matters is that they're close enough that the white dwarf can steal matter from its partner, and build it up like a smothering blanket of potential explosiveness. When the stolen amount reaches 1.4 times the mass of the sun, the white dwarf explodes as a supernova and completely vaporizes. Because of this 1.4 ratio, astronomers use Type Ia supernovae as "standard candles" to measure distances in the universe. Since they know how much energy it detonated with, astronomers can calculate the distance to the explosion. There are probably other, even more rare events that can trigger supernovae, and even more powerful hypernovae and gamma ray bursts. These probably involve collisions between stars, white dwarfs and even neutron stars. As you've probably heard, physicists use particle accelerators to create more massive elements on the Periodic Table. Elements like ununseptium and ununtrium. It takes tremendous energy to create these elements in the first place, and they only last for a fraction of a second. But in supernovae, these elements would be created, and many others. And we know there are no stable elements further up the periodic table because they're not here today. A supernova is a far better matter cruncher than any particle accelerator we could ever imagine. Next time you hear a story about a supernova, listen carefully for what kind of supernova it was: Type I or Type II. How much mass did the star have? That'll help your imagination wrap your brain around this amazing event.
Citation: What are the different kinds of supernovae? (2016, March 15) retrieved 19 October 2022 from https://phys.org/news/2016-03-kinds-supernovae.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
Type Ia supernovae are an important tool for modern astronomy. They are thought to occur when a white dwarf star captures mass beyond the Chandrasekhar limit, triggering a cataclysmic explosion. Because that limit is the same for all white dwarfs, Type Ia supernovae all have about the same maximum brightness. Thus, they can be used as standard candles to determine galactic distances. Observations of Type Ia supernova led to the discovery of dark energy and that cosmic expansion is accelerating. While these supernovae have revolutionized our understanding of the universe, they aren’t quite as standard as we first proposed. Some, such as SN 1991T are much brighter, while others, such as SN 1991bg are much dimmer. There is also a variation known as Type Iax, where the white dwarf isn’t completely destroyed by the explosion. We can generally take these variations into account when calculating stellar distances, but it would be good to have a better understanding of the mechanism behind their maximum brightness. According to theoretical models, the maximum brightness of a Type Ia supernova depends upon the mass and central density of the white dwarf before it explodes. But how could these values be measured? After all, we typically only discover these stars after they explode. Fortunately, a new study in The Astrophysical Journal Letters shows how it can be done. The study looked at a supernova remnant known as 3C 397. It’s about 33,000 light-years from Earth and probably exploded about 2,000 years ago. Because the supernova was relatively close and recent, astronomers can get a good view of the material cast out by the explosion. An earlier study of the remnant debris suggests that the original white dwarf star was very close to the Chandrasekhar limit when it exploded. This study focused on the observations of particular isotopes within the debris, particularly those of titanium and chromium. It’s the first time titanium has been observed in a Type Ia remnant. When the team compared the amount of titanium and chromium to those of iron and nickel, they found an unexpectedly high ratio. This is important because the ratios of Ti/Ni and Cr/Ni are crucially dependent upon the core density of the progenitor star. Based on their observations, the team determined that the core of 3C 397 was 2-3 times higher than generally assumed for white dwarfs. Thus, the explosion was likely much brighter than a typical Type Ia supernovae. While this is a single study of a single supernova, it shows how the ratio of elements can determine white dwarf core densities. This can be used to better calibrate the maximum brightness of Type Ia supernovae, better standardizing the candle for cosmologists. Reference: Ohshiro, Yuken, et al. “Discovery of a Highly Neutronized Ejecta Clump in the Type Ia Supernova Remnant 3C 397.” The Astrophysical Journal Letters 913.2 (2021): L34. |
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