Final answer:
The spectrum of a Type Ia supernova is identifiable by the absence of hydrogen and presence of strong silicon absorption lines, which arise from the white dwarf's composition and the lack of hydrogen.
Step-by-step explanation:
The spectrum of a Type Ia supernova can be identified because it lacks evidence of hydrogen. These supernovae originate from a white dwarf in a binary system accreting enough material from a companion star to exceed the Chandrasekhar limit, then collapsing and exploding. Type Ia supernovae spectra are characterized by strong silicon absorption lines, a product of the fusion of carbon and oxygen and indicative of the white dwarf's composition. Unlike massive star collapse-related supernovae, or Type II, Type Ia supernovae do not show hydrogen in their spectra because the white dwarf remnants are primarily composed of carbon and oxygen, with hydrogen being absent. Furthermore, these supernovae serve as "standard bulbs" for astronomers due to the consistent energy output and luminosity, which make them useful for measuring distances in the universe.