Type I and type II supernovae have some features in common, while others are very different.

Type I supernovae consist of exploding white dwarf stars composed primarily of oxygen and carbon. The white dwarf absorbs the mass of a nearby colliding neutron star to increase to a mass of 1.4 times our sun. The resulting density and temperature conditions result in the carbon starting to burn explosively. In a second, a nuclear fireball is created and the entire star flies to the coming kingdom. There is no remainder. All of the star’s mass is ejected into space at speeds of 6,000 to 8,000 miles per second. These shells consist mainly of heavier elements resulting from the nuclear fusion process, plus a small amount of oxygen and carbon. White dwarfs contain almost no hydrogen and post-explosion measurements have been consistent with this. Very little hydrogen has been found in the spectra of Type I supernovae.

This is not true for Type II supernovae. Type II supernovae occur when stars with masses greater than eight solar masses run out of nuclear energy and implode on themselves asymmetrically. The exact causes of the Type II explosion remain undetermined. Neutrino ejection from the condensed nucleus is known to be a factor, as neutrinos contain hundreds of times the energy needed to trigger the explosion. However, it has been speculated that the neutrinos may actually carry too much energy away from the star. The core is left with very little energy for the necessary combustion. Theories have been proposed in which the emission of streams of mass energy known as “jets” or the creation of acoustic shock waves are responsible for the explosion. Computer simulations hope to shed more light on these theories in the future.

Another known difference between Type I supernovae and Type II supernovae lies in the characteristics of the light spectra emitted during the explosion. Type I supernovae are always nearly 4 billion times brighter than our Sun at the time of explosion. It follows a pattern of light that steadily decreases. The subsequent decay of light at this constant rate is due to radioactive decay of the heavier elements mentioned above. Radioactive decay follows the universal time law of half-lives, with different elements having different half-lives as one of their properties. This can be used to measure the distance to nearby stars by considering Type I supernovae as so-called “standard candles”.

In Type II supernovae, the “light curve” rises to a plateau a few months after the explosion. This comes from the expansion and cooling of the outer boundaries of the resulting ball of gas. Computer simulations verify this through the presence of large amounts of helium and hydrogen in the Type II light spectrum, gases that would be expected to be found after the decay of stellar materials from this type of explosion.

Type II supernovae are never found in elliptical galaxies. Rather, their stars are usually found in the disks of the spiral arms of galaxies. For this reason, they are thought to be Population I stars. Population I stars make up about two percent of the stars and tend to form from heavier elements from earlier giant stars. They are young, hot and bright.

Type I supernovae, on the other hand, usually occur in the core of elliptical galaxies. They are believed to be from the Population Stars II. Population II stars are older, cooler, less luminous, and composed of lighter elements.

Although the differences between Type I and Type II supernovae make them seem as different as apples and oranges, they both originate from the explosion of supermassive stars due to the collapse of their core and their subsequent fusion processes. Therefore, they are in the same class of natural phenomena. Both play a critical role in stellar evolution, and both contain enough unanswered questions to keep astrophysicists curious about the unforeseeable future.