Supernovae
* Can outshine an entire galaxy (L ≈ 1010 Lsun for weeks.
* Produce copious neutrinos, and heavy elements.
Supernova Remnants
•
Material ejected by SN explosions.
•
Distribution of heavy elements into space.
•
Trigger for later star formation.
All matter heavier than carbon was produced in the cores of stars that exploded
as SN.
Recent Supernovae
1987
1885
1604
1572
1054
Large Magellanic Cloud
Andromeda
Kepler’s
Tycho’s
Crab
SN 1987a
References: popular: Paul Murdin (1990) “End in Fire, The Supernova in the
Large Megallanic Cloud,” Cambridge University Press.
Research: (1989) “Supernovae: The Tenth Santa Cruz Workshop in Astronomy
and Astrophysics,” ed. S. E. Woosley, Springer-Verlag
SN 1987a is of great interest because it was nearby (in the LMC at
170,000 l.y. or 56 kpc), and bright (up to V = 4.4 mag.). It could be
studied in unprecedented detail.
- see photo and light curve.
Note: the rapid fading, then slow rebrightening are atypical phenomena in
type II SN. Then there was an unusually rapid drop to the radioactive tail.
Before and after views (actually, after and before.
The progenitor star, Sk -69 202, was a blue supergiant.
SN87a was also detected by ν observatories:
1987 Feb. 23 02:52 UT
Mt. Blanc Neutrino Obs.
5νs within 7 sec.
7 ≤ E ≤ 11 MeV
Kamiokande II, Japan
12νs within 10 sec.
8 ≤ E ≤ 35 MeV
IMB, Ohio
8νs within 6 sec.
20 ≤ E ≤ 40 MeV
Baksan, USSR
5νs within 9 sec.
13 ≤ E ≤ 18 MeV
1987 Feb. 23 07:35 UT
Two bursts or one?
Why second brightness peak?
56Ni
28
56Co
27
Radioactive decay.
+ e- –––> 56Co27 + γ + ν
(τ = 6 days),
+ e- –––> 56Fe26 + γ + ν
(τ = 77 days),
[56Co27 –––> 56Fe26 + γ + e- + ν]
Why do massive stars go supernova?
It’s a result of one of the most basic properties of nuclear physics - the curve of
binding energy.
When a star tries to burn beyond 56Fe,
Eb/A (MeV)
the core absorbs energy.
Fe burning accelerates collapse.
8
Fe56
4
40
80
A
Energy absorbed
Reduced Pressure
More burning
Reduce support
against gravity
Higher Pressure
Collapse
The cycle continues until bounce or collapse to a black hole.
Fe core collapses rapidly to incredibly high density and temperature.
- Enormous amount of gravitational energy released by the collapse and bounce.
- The energy is deposited in the envelope, which is violently ejected.
- The high density and temperature –––> synthesis of all elements heavier than
iron, within a few seconds!
This is a supernova explosion!
Types of SN