I’ve heard about them and know that they are used as standard candles, but what exactly are they? What makes them differ from other supernovae? Also, are they only special because of their use as standard candles, or are the use for something else?


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    $\begingroup$ Hi Nidhish, have you looked up "Type Ia Supernova" in Wikipedia? There's a comprehensive explanation available there. You can then come back to our site if there's something you still don't understand after having done your basic research. :-) $\endgroup$ – Chappo Nov 11 '18 at 12:51

I think these links are highly useful for you.

  1. Standard Candle and other applications


This type Ia category of supernovae produces consistent peak luminosity because of the uniform mass of white dwarfs that explode via the accretion mechanism. The stability of this value allows these explosions to be used as standard candles to measure the distance to their host galaxies because the visual magnitude of the supernovae depends primarily on the distance. (...)

The similarity in the absolute luminosity profiles of nearly all known Type Ia supernovae has led to their use as a secondary standard candle in extragalactic astronomy. Improved calibrations of the Cepheid variable distance scale and direct geometric distance measurements to NGC 4258 from the dynamics of maser emission, when combined with the Hubble diagram of the Type Ia supernova distances, have led to an improved value of the Hubble constant.

In 1998, observations of distant Type Ia supernovae indicated the unexpected result that the universe seems to undergo an accelerating expansion. Three members from two teams were subsequently awarded Nobel Prizes for this discovery. (...)

It has been discovered that Type Ia supernovae that were considered the same are in fact different; moreover, a form of the Type Ia supernova that is relatively infrequent today was far more common earlier in the history of the universe. This could have far-reaching cosmological significance and could lead to a revision of estimation of the rate of expansion of the universe and the prevalence of dark energy.

  1. Difference between other Supernovae


This table in the link shows the differences between them very precisely.

Type Ia supernovae occur a white dwarf accretes a material from the companion in a binary system. When the white dwarf excess the Chandrasekhar limit, which is about 1.4 solar mass, it explodes. Only the explosion happens when they exceed that limit, that's why the luminosity of these explosions are nearly constant. So we can use this as a 'standard candle.'

Type II supernovae, in short, are the massive star explosion. A star must have at least 8 times, but no more than 40 to 50 times, the mass of the Sun. So their luminosities are quite different from each other, therefore we cannot use these as a standard candle like SN Type Ia.


Type Ia is a thermonuclear explosion of a white dwarf. The other type of supernovae is core-collapse supernovae, which happen in massive $>$8 M$_\odot$ at zero age main sequence.

SNe Ia are used for measuring distances (as standard candles) and measuring cosmological parameters. SNe Ia are also well known to significantly produce Fe group compared to other types of SNe, therefore they are natural sites for studying related nucleosynthesis. There are some more reasons why SNe Ia are interesting.


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