Question

Type II supernovae show prominent lines of hydrogen in their spectra, whereas hydrogen lines are absent in spectra of Type Ia supernovae. Explain. (Hint: Think about the type of star that gives rise to each of the two types of supernova.)

A) Massive stars contain large amounts of hydrogen, whereas white dwarfs are mostly carbon and oxygen.
B) White dwarfs have a thick surface layer of hydrogen, whereas neutron stars contain no hydrogen at all.
C) Massive stars have fused all their hydrogen into heavier elements, whereas low-mass stars still have large hydrogen-rich envelopes.
D) Massive stars contain large amounts of hydrogen, whereas neutron stars contain no hydrogen at all.

Answer 1

Type II supernovae spectra show hydrogen lines because they come from massive stars that still have hydrogen, while Type Ia supernovae lack hydrogen lines as they originate from carbon and oxygen-rich white dwarfs which have exceeded the Chandrasekhar limit.

Step-by-step explanation:

The prominent hydrogen lines in the spectra of Type II supernovae are indicative of the progenitor star's composition. These supernovae originate from the death of massive stars which contain large amounts of hydrogen in their outer envelopes. In the course of their evolution, these massive stars have not fully converted their hydrogen into heavier elements, so when they explode, the spectra clearly show hydrogen lines.

On the other hand, Type Ia supernovae do not show hydrogen lines in their spectra because they arise from white dwarfs, which are remnants of stars that have shed their outer hydrogen layers. White dwarfs are primarily composed of carbon and oxygen, and they explode when they accrete enough material from a companion star to exceed the Chandrasekhar limit, thus lacking a hydrogen-rich envelope that would produce hydrogen lines in their spectra. Moreover, the presence of strong silicon absorption lines in Type Ia supernovae further supports their carbon and oxygen-rich nature, as silicon is a byproduct of the fusion of these elements.