Astro 150 Spring 2005: Lecture 17 page 1
Reading: Chapter 18, Sect. 18.1-18.3
OBAFGKM Winners!
Exam 2: Thursday after break, March 24; essay (next) Tuesday
Brief review of last time: Stellar Evolution II
•White Dwarf Stars
•hot but faint –> very small (Sirius B)
•supported by electron degeneracy pressure
•evolution through cooling
•Final evolution: 8Msun < M < 25Msun
•burns C, etc. but with diminising efficiency
•onion-skin structure
•iron burning eats energy
•Supernova
•iron core collapse, rebound (in seconds)
•synthesis of all heavy elements
•expanding supernova remnant
•Neutron Stars
•supported by neutron degeneracy
•M ~ 2Msun, R ~ 20 km: density ~ 1014 g/cc
•small and very faint
Astro 150 Spring 2005: Lecture 17 page 2
Neutron Stars
•Mass ~ 2.0 Msun
•Radius ~ 0.00002 Rsun
•Temperature ~ 5x105 K
so, L/Lsun ~ 0.001 - nearly all in X-ray
rarity of neutron stars (end product of O, B star
evolution) means:
!closest is still pretty far away
!very unlikely to see in optical (or even X-ray)
L
Lsun
=R
Rsun
2T
Tsun
4
Astro 150 Spring 2005: Lecture 17 page 3
Discovery of Neutron Stars - Pulsars (1967)
•1967: S. Jocelyn Bell discovers a radio signal:
•regularly pulsing
•rapid
(once every 1.33 seconds)
•extraterrestrial
•aliens? LGM1, LGM2, ...
•Neutron stars !
•1968: Tommy Gold (and Franco Pacini)
•pulsars are rapidly rotating neutron stars
•beaming by e- in magnetic field
•NS rotation sweeps beams
•confirmed by measures change in spin rate
PSR 0329:
0.72 s
1974 Nobel Prize to... Tony Hewish
(Bell’s advisor ?!#@)
Astro 150 Spring 2005: Lecture 17 page 4
