From the May 2012 issue

The different types of supernovae

Not all supernovae are created equal. Here is a brief description of the four main categories of exploding stars.
By | Published: May 29, 2012
Scientists classify Supernova 1987a in the nearby Large Magellanic Cloud as a type II — meaning it resulted from the collapse, and ensuing explosion, of a massive star. Credit: NASA/ESA/P. Challis and R. Kirshner (Harvard-Smithsonian CfA)
Supernovae are stars that suddenly increase drastically in brightness (billions of times more luminous than the Sun), outshining their own galaxies. They reach this brightness in just a few hours and take from weeks to months to fade.

Scientists classify different types of supernovae by their emitted light signatures (called spectra); these show what elements the original star created and thus released into space after it exploded.

Type Ia supernovae

• Their spectra show very little hydrogen and a lot of carbon; they also show silicon, calcium, and elements up to iron (due to fusion during the intense explosions).

• Astronomers believe this type of supernova results from a white dwarf (the carbon-oxygen remnant of a once Sun-like star) that has collected too much material for its internal pressure to withstand. Once its mass reaches 1.4 times that of our Sun, the white dwarf collapses, which causes its internal temperature to rapidly rise. Then, the carbon fuses, and the entire star explodes as a carbon-detonation supernova. The initial white dwarf can collect material from a company red giant star or from colliding with another white dwarf.

Type Ib supernovae

 • Their spectra contain very little hydrogen; they also show helium.

 • Scientists think this type of supernova results from the death of a star at least 25 times the Sun’s mass. The star sheds material from its gaseous envelope late in its life (hence the lack of hydrogen in its spectrum). The star then implodes, bounces back, and explodes.

Type Ic supernovae

• Their spectra contain very little hydrogen or helium.
• Scientists believe this type forms like a type Ib supernova; collectively, these objects are called “stripped core-collapse supernovae.”

Type II supernovae

• This type of supernova has a lot of hydrogen and helium in its spectrum.

• Astronomers think this type results from the death of a star larger than eight times our Sun’s mass. Such a star can fuse elements up to iron. Its core then heats up, implodes, and bounces back to explode, spewing heavy elements into space. The enormous explosion leaves behind a neutron star or a black hole, depending on the mass of the initial star. Type II supernovae are called “core collapse supernovae.”