What are the differences between type I and type II supervovae?

Question

How can we tell which type we are observing? Why do type II explode? What is the type II supernovae core made of just before the explosion that destroys it?

Answer 1

The distinguishing characteristic is the presence of a hydrogen spectrum in a type II supernova. A type II supernova is the result of core collapse in a massive star; the hydrogen is present in the outer envelope of the star.

A type Ia supernova is caused by material falling onto a white dwarf and causing its mass to exceed the Chandrasekhar limit. At that point the gravitational pressure causes the entire white dwarf to undergo instantaneous fusion. Because the entire star explodes, and it happens at about the same mass in almost every case, type Ia supernovae all have the same luminosity and can be used as "standard candles" to estimate the distance to the galaxies they occur in.

Type Ib and Ic supernovae are collapsing stars like type II, but there is no hydrogen in their spectra. These are from massive stars that have shed their outer layers, such as Wolf-Rayet stars.

Answer 2

1

Answer 3

You can't tell just by looking - you need the right telescope and you need to analyse the spectrographic data.

Supernovae of the general category Type I are classified based on the lack of hydrogen lines in their spectra and are generally the explosions of white dwarf stars (so they are less than 1.3 solar masses).

A Type Ia supernova is the explosion of a white dwarf star.
Type Ib lacks an absorption line of singly-ionized silicon at a wavelength of 635.5 nanometres.
Type Ic supernovae are distinguished from Type Ib in that they also lack lines of helium.


Type II supernova, or core-collapse supernova, result from the internal collapse and violent explosion of a massive star. Stars must have at least 9 times the mass of the Sun in order to undergo a core-collapse. They display lines of hydrogen in their spectra and are more than 1.3 solar masses.