The way I understand distance is measured for far out objects is by binary star supernova, since at the point of explosion there's is always same amount of energy released.

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But then supernova can also come from single star that has enough mass in it.

When measuring distance how do we distinguish when supernova comes from binary star and not single one?

  • 1
    $\begingroup$ Distance is measured by light curves produced by type Ia SNe. We can distinguish between the two models (singly degenerate vs doubly) by looking for the remaining companion star (not always/usually possible due to distances, but we have some remnants in our own galaxy...) $\endgroup$
    – Kyle Kanos
    Dec 17 '15 at 18:57

The supernovae used to estimate distance are type Ia supernovae, resulting from the thermonuclear explosion of a white dwarf. These result in supernova light curves that are remarkably consistent (though not identical). These light curves can be matched with similar observations in the local universe to estimate a distance.

Supernovae occurring in single, massive stars are known as type II core-collapse supernovae. These have very different characteristics and a diversity of light curve shapes and peak luminosities. They cannot easily be used to estimate a distance.

The two are easily distinguished by obtaining a spectrum. Type II supernovae occur in stars with extensive hydrogen envelopes and their spectra evidence absorption lines due to hydrogen. Type Ia supernovae arise in carbon/oxygen (or possibly helium) white dwarfs with very little hydrogen. Their spectra do not evidence hydrogen absorption lines.

A few core collapse supernovae also do not show hydrogen lines and are thought to be due to an explosion in a massive star that has already lost its hydrogen envelopes. However, these type Ib and Ic supernovae are distinguished from type Ia supernovae because they lack the strong signature of silicon in their spectra. The silicon absorption in type Ia supernovae is because silicon is a major product of the nuclear burning of carbon and oxygen in the exploding white dwarf.


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