Neutron Capture

Note: S-process material predicts proton rich heavy nuclei
R-process material predicts neutron rich heavy material.

On earth, 235U (1/2 life of 750 million years) comes from S-process and is reactor core fuel.

but 238U (1/2 life of 4.5 billion years) comes from R-process and this drives plate tectonics.

The Solar system has both R and S process material in it.

As a result, the remnants of supernova contain the entire periodic table of elements.

Supernova in external galaxies are relatively easy to detect with modern imaging technology.

A supernova will radiate luminosity at about a level of 10% that of its host galaxy for a period of 2-3 weeks.

The following is an image galaxy of some recent SN occurences in nearby galaxies:

PMO Image

Implementing a supernova search program is relatively straightforward to do and can be done with automated robotic telescopes.

As a result, SN detection efficiency over time is strongly increasing.

Historical Supernova In Our Galaxy
Year Peak Mag. Constellation Distance
Light Years

AD 185




AD 386




AD 1006




AD 1054




AD 1181




AD 1572




AD 1604




AD 1671




Candidate stars for next supernova:

These are all a lot closer than past Galactic SN and therefore will be quite bright and clearly visible in the daytime sky. Radiation damage is a small possibility as well.

There is some evidence (but weak) that 5 million years ago, there was a small extinction event induced by a supernova explosion nearby.

The first extragalactic supernova ever discovered was SN 1885A near the nucleus of M31 (the famous "Andromeda Galaxy") on 20 August 1885. SN 1885A had an apparent visual magnitude of 5.85 - it would have been just barely visible to the naked eye had not the glow from M31 overwhelmed it

Supernova Rates:

To first order, one would think that the occurence of SN is correlated to where most of the stars are. But anecdotal evidence is strange.

For instance, the Coma Cluster

which has at least 1014 stars in it, hasn't had a supernova occur since 1935. This is a factor of 1000 below the canonical rate.

The galaxy NGC 5253, which has 109 stars in it, has had 3 SN occur in the last 20 years.

Supernova Light Curves:

These light curves are powered by radioactive decay in two stages.

Note also that current astrophysical lore argues that the Peak luminosity of type Ia is a "constant". If this is true, then such objects are useful cosmological probes (see below).

There is, however, a strong minority viewpoint that the assumption of constant peak luminosity is bullshit there is no strong theoretical expectation for this.

Stage 1 is the decay of 56Ni to 56Co This has a 1/2 life of 6.1 days and predicts that the SN luminosity decays at the rate of 11% per day.

Stage 2 is the decay of 56Co to 56Fe This has a 1/2 life of 77 days and predicts that the SN luminosity decays at the rate of 1% per day.

These two stages are reflected in this light curve:

Distant Supernova as Cosmological Probes

We will more critically examine this data in the second half of the couse as we move away from stellar evolution and onto more cosmological issues.