Supernovae are the bright ends of some of the largest stars in the universe. When the star can no longer fuse elements, the core collapses and rips the star apart. The explosion is called the supernova, but the thrown out material is called the supernova remnant. The crab nebula is an example of a remnant.
Supernovae can be categorised into two main branches: type I and type II.
Type I supernovae are created from white dwarfs in a binary system. The dwarf will engulf lots of mass from its binary companion star until it reaches about 1.4 solar masses. After that it explodes into a supernova!
A supernovae created by this method will quickly reach peak luminosity, and then slowly die down. They also show no hydrogen lines whatsoever in their spectra.
Type I can be split into three branches: 1a, 1b, and 1c.
1a are almost identical to each other in luminosity, and are frequently used for measuring distances. They have a distinctly strong silicon line in their spectra, and a few other silicon lines. 1994D is an example of a 1a.
1b are characterised by helium lines. An example is SN 2008D. It lives in galaxy NCG 2770. It looks quite dim in the X-ray picture below.
Here it is again. It’s the white dot at the top of the galaxy, which may be difficult to see.
Other supernovae that have no hydrogen, no silicon, or no helium are all classed as 1c.
Type 1ax are hypothesised dimmer versions of type 1a. In this case the white dwarf hasn’t completely exploded, and is called a zombie star. One example could be SN 2012Z from the galaxy NGC 1309, formerly a binary system of a large star and a white dwarf.
Type II supernovae are created from core collapse. A giant star above 10 solar masses will collapse from such a high gravitational force that material is thrown out at immensely high speeds and distances.
Unlike type I, supernovae that belong to type II do have hydrogen in their spectra. They can be split into two main branches: II-P and II-L.
Most Type II supernovae peak in luminosity sharply, then decrease slightly until they plateau. They stay in a plateau for a while, and then start to decrease normally. Those that do plateau are called type II-P, and the ones that don’t (just like type Is) are called type II-L.
I’ve probably given you a headache from all the roman numerals, so this is a visual representation of their luminosities.
That’s it for this week! I hope you enjoyed learning about supernovae, as I sure have!
I’m surprised Type I supernovae don’t have any hydrogen lines whatsoever. Is that because all the hydrogen gets fused into other elements, or is all the hydrogen blown off into space?
Quite a lot of the hydrogen is lost when the white dwarf ages. The outer layers shed off and make a planetary nebula, and the dwarf slowly becomes a carbon-rich white dwarf. During the supernova, the hydrogen from the companion star probably just fuses into heavier elements, but that process isn’t too clear yet.
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