Supernovas

Supernova = When gravity wins… core collapses and a star explodes.

Two main types: Type I and Type II

Relatively rare: occur every 50-100 years in Milky Way… probably similar in other galaxies.

Supernovas

The only way heavy elements form.

Expanding shock wave from explosion can trigger the formation of new stars…like our Sun

Life Cycle of Large Star

Crab Nebula

Observations

Earliest recorded SN by Chinese in 185 AD.

First widely observed SN in 1054 - created the Crab Nebula.

Last one observed in 1604 (by Kepler).

Types

Type is determined by whether Hydrogen is detected in spectrum.

Type I = no hydrogen detected

Type II = hydrogen detected

Type I

Occur in binary star systems when a white dwarf steals matter from a companion star.

Once matter reaches 1.4 solar masses, star with explode within seconds…leaving nothing.

Since all Type 1 supernovas are same size, they’re all the same brightness.

As a result, used to measure distances to other stars (standard candles).

Type II

Occurs if star is over 8x mass of the Sun.

Explosion produces more energy than our Sun will produce in its lifetime.

Can briefly outshine a galaxy, then fades within a week or few months.

SN 1987A – before/after

Type II

How it happens:

1. Hydrogen runs out, then helium, then carbon, etc., until iron is produced.

2. Iron does not fuse… within seconds gravity causes core to collapse, then explode.

Type II

If less than 20x mass of sun, neutrinos stop complete collapse… creating neutron star.

If more than 20x mass of sun, neutrinos fail to stop collapse…. black hole is formed.

SN 1987A – early shock wave

SN 1987A - shock wave (1999)

SN 1987A – Chandra (2005)