The biggest supernovae are called hypergiants and smaller ones are called supergiants. They are massive: because of gravity they use up their energy very quickly. Normally they only live for a few million years.
During the explosion, the total energy radiated by supernovae may briefly outshine the entire output of a galaxy. They emit energy equal to that of the whole lifetime of a solar-like star. The explosion blows of its stellar material away from the star, at velocities up to 30,000 km/s or 10% of the speed of light. This drives a shock wave into the surrounding interstellar medium. This sweeps up an expanding shell of gas and dust, which we see as a supernova remnant. After exploding, what is left becomes a black hole or a neutron star.
Supernova explosions happen rarely. In our own galaxy, the Milky Way, the last supernova happened in the year 1604. We can see supernovas in other galaxies too. Every year we see 300 supernovas in other galaxies, because there are so many galaxies. Sometimes they are brighter than the whole rest of the galaxy.
Types[change | change source]
Supernovas are usually sorted into Type I and Type II supernovas.
Type I supernovas have absorption lines that make them look like they do not have hydrogen in them. One important kind of Type I supernovas are Type Ia supernovas. These supernovas are very bright for a short amount of time. Then they get less bright very quickly. Type Ia supernovas happen when a white dwarf star is orbiting a big star. Sometimes, the white dwarf star sucks matter off of the big star. When the white dwarf gets to be about 1.4 times the mass of the sun, it collapses. This makes lots of energy and light, which is why supernovas are very bright. Type 1A have mostly the same brightness.
Type II supernovas have absorption lines that make them look like they do have hydrogen in them. They get very bright, and then they stay very bright for a long time. In a star, nuclear fusion turns hydrogen into helium. In very large stars, helium gets turned into oxygen, and so on. When nuclear fusion happens, it makes lots of energy and heat. This makes the star stay hot. However, when iron is formed, it cannot be turned into any other elements. When there is enough iron, there is less heat, so the star gets smaller. Then the star collapses which makes lots of energy and light.
Supernovas and life[change | change source]
Without supernovas there would be no life on Earth. This is because many of the chemical elements were made in supernova explosions. These are called "heavy elements". Heavy elements are needed to make living things. The supernova is the only way heavy elements can be made. Other elements were made by fusion in stars. Heavy elements need very high temperature and pressure to form. In a macho supernova explosion the temperature and pressure are so high that heavy elements can be made. Scientists call this supernova nucleosynthesis.
It could be dangerous if a supernova explosion happened very close to the Earth. The explosion is very big and many kinds of dangerous radiation are formed. But we do not have to be afraid. Only very big stars can explode as supernovas. There are no stars big enough near the Earth and if there was it would take millions of years for it to happen.
Important supernovas[change | change source]
SN 1572 was seen by Tycho Brahe. This supernova helped astronomers learn that things in space could change. SN 1604 was seen by Johannes Kepler. It was the last supernova close enough to be seen from Earth's northern hemisphere without a telescope. SN 1987A is the only supernova so close that scientists could find neutrinos from it. SN 1987A was also bright enough to see without a telescope. People in the southern hemisphere saw it.
Effects on Earth[change | change source]
The Earth does have traces of past supernovae. Traces of radioactive iron-60, a strong indicator of supernova debris, is buried in the sea floor right across the globe.
The "local bubble" is a ballooning region of hot gas, 600 light-years across. It surrounds the Solar System and dominates our stellar neighbourhood. It was formed by over a dozen supernovae blowing up in a nearby moving clump of stars. This happened between 2.3 million and 1.5 million years ago. This roughly corresponds with the start of the Pleistocene ice ages. The connection may be accidental.
Related pages[change | change source]
References[change | change source]
- This is the cause of all types of supernova except type Ia.
- Giacobbe, Frederick W. 2005. How a Type II supernova explodes. Electronic Journal of Theoretical Physics 2 (6): 30–38. 
- Heger, Alexander et al 2003. How massive single stars end their life. Astrophysical Journal. 591: 288. 
- Tyler, Pat (26 Jun 2003). "Supernova". NASA HEASARC: Education and Public Information. http://heasarc.gsfc.nasa.gov/docs/snr.html. Retrieved 29 Jan 2013.
- "Supernovae". Georgia State University. http://hyperphysics.phy-astr.gsu.edu/hbase/astro/snovcn.html. Retrieved 29 Jan 2013.
- Calar Alto Observatory-CAHA (4 Dec 2008). "Blast from the past: astronomers resurrect 16th-century supernova". Science Daily. http://www.sciencedaily.com/releases/2008/12/081203133809.htm. Retrieved 29 Jan 2013.
- Frommert, Hartmut; Kronberg, Christine. "SN 1604, Kepler's Supernova". http://spider.seds.org/spider/Vars/sn1604.html. Retrieved 29 Jan 2013.
- "Twenty Years after SN1987a". 25 Feb 2007. http://sn1987a-20th.physics.uci.edu/. Retrieved 29 Jan 2013.
- Webb, Jonathan 2015. Exploding stars left recent, radioactive mark on Earth. BBC News Science & Environment.