Supernovae and Gamma-Ray Bursts

Summary of Post-Main-Sequence Evolution of Stars

M > 8 Msun

M < 4 Msun

Subsequent ignition of nuclear

reactions involving heavier

elements

Fusion stops at formation of C,O core.

Fusion proceeds; formation

of Fe core.

Supernova

Fusion of Heavier Elements

Final stages of fusion happen extremely rapidly: Si burning lasts only for ~ 2 days.

126C + 4

2He → 168O +

168O + 4

2He → 2010Ne +

168O + 16

8O → 2814Si + 4

2He

Onset of Si burning at T ~ 3x109 K

→ formation of S, Ar, …;

→ formation of 5426Fe and 56

26Fe

→ iron core

The Life “Clock” of a Massive Star (> 8 Msun)

Let’s compress a massive star’s life into one day…

12 12

3

45

67

8

9

1011

12 12

3

45

67

8

9

1011

Life on the Main Sequence

+ Expansion to Red Giant: 22 h, 24 min.

H burning

H → He

H → He

He → C, O

He burning:

(Horizontal Branch) 1 h, 35 min, 53 s

H → HeHe → C, O

C → Ne, Na, Mg, O

Ne → O, Mg

H → He He → C, O

C → Ne, Na, Mg, O12 1

2

3

45

67

8

9

1011

C burning:

6.99 s

Ne burning:

6 ms 23:59:59.996

H → HeHe → C, O

C → Ne, Na, Mg, O

Ne → O, Mg

O burning:

3.97 ms 23:59:59.99997

O → Si, S, P

H → HeHe → C, O

C → Ne, Na, Mg, O

Ne → O, Mg

Si burning:

0.03 ms

The final 0.03 msec!!

O → Si, S, P

Si → Fe, Co, Ni

Observations of Supernovae

Supernovae can easily be seen in distant galaxies.

Total energy output:

Ee ~ 3x1053 erg (~

100 L0 tlife,0)

Ekin ~ 1051 erg

Eph ~ 1049 erg

Lpk ~ 1043 erg/s ~ 109 L0

~ Lgalaxy!

SN 2006X in M 100

Observed with the MDM 1.3 m telescope

Type I and II SupernovaeCore collapse of a massive star:

Type II Supernova

Collapse of an accreting White Dwarf exceeding the Chandrasekhar mass limit

→ Type Ia Supernova.

Type I: No hydrogen lines in the spectrum

Type II: Hydrogen lines in the spectrum

Type Ib: He-rich

Type Ic: He-poor

Type II P

Type II L

Light curve shapes

dominated by delayed energy

input due to radioactive

decay of 5628Ni

The Famous Supernova of 1987:SN 1987A

Before At maximumUnusual type II

Supernova in the Large Magellanic

Cloud in Feb. 1987

Progenitor: Blue supergiant (denser than normal SN II

progenitor)

20 M0;

lost ~ 1.4 – 1.6 M0 prior to SN

Evolved from red to blue ~ 40,000 yr

prior to SN

The Remnant of SN 1987ARing due to SN ejecta

catching up with pre-SN stellar wind; also

observable in X-rays.

vej ~ 0.1 c

Neutrinos from SN1987 have been observed by

Kamiokande (Japan)

Escape before shock becomes opaque to

neutrinos → before peak of light curve

provided firm upper limit on e mass: me < 16 eV

Remnant of SN1978A in X-rays

Color contours: Chandra

X-ray image

White contours:

HST optical image