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Unformatted text preview: e II supernova
EE8086 – Astronomy: Stars, Galaxies & Cosmology All supernovae shine brilliantly 10b Suns. Supernova type distinguished by their light. white dwarf supernovae lack H lines & fade steadily with time
star type fade in 2 distinct stages massive
Page 15 EE8086 – Astronomy: Stars, Galaxies & Cosmology Page 16 Distance Measurement with White Dwarf Supernova White dwarf supernovae always occur when the 1.4 Msun
dwarf supernovae always occur when the
limit is reached same maximum luminosities. good distance indicators
more luminous than Cepheid variable stars
can measure out to greater distances
measure out to greater distances Yet Distance of the white dwarf supernova (& its galaxy)
determined using the inverse square law.
= A ball of neutrons created by the collapse of the iron core
in massive star supernovae.
in a massive star supernovae. Typically No mass limit for massive star supernovae. Knowing luminosity of one white dwarf supernova luminosity of all are known. Apparent
brightness Neutron Star 10 Km in radius more massive than the Sun
more massive than the Sun Neutron stars are very dense. 1.5Msun with diameter of 10~20 km 1012 g/cm3 paper clip of this
clip of this
density outweigh Mount Everest luminosity
4d 2 EE8086 – Astronomy: Stars, Galaxies & Cosmology Page 17 Neutron Stars EE8086 – Astronomy: Stars, Galaxies & Cosmology Page 18 Pulsars In a neutron star, it is neutrons rather than electrons
that are closely packed.
that are closely packed. Neutron degeneracy pressure stops collapse of core
with mass < 3Msun .
ith mass 3M Pressure arises when neutrons are closely packed Supports the core against crush of gravity Light Curve of Jocelyn Bell’s Pulsar Graduate student Jocelyn Bell & her advisor discovered
a radio source in the Cygnus constellation in 1967. Rotate very rapidly with period
very rapidly with period
of 0.03~4 s. sharp pulse recurring every 1.33 s 300 pc (978 light years) away Magnetic fields are 10t times
stronger than Earth’s.
EE8086 – Astronomy: Stars, Galaxies & Cosmology They called it a pulsar (Pulsating radio source).
called it pulsar (Pulsating radio source)
Page 19 EE8086 – Astronomy: Stars, Galaxies & Cosmology Page 20 Pulsar
Pulsar in Crab Nebula Pulsars are Neutron Stars! A pulsar is a spining neutron star that beams radiation along
its magnetic axis. Pulses came at very
precise intervals. other massive object can spin so fast (< 1s-1 for white dwarf) Radio emission concentrated at magnetic poles magnetic field trillion times of Earth’s no man-made? Mystery solved by late
1968 when a pulsar was
discovered in the heart
of Crab Nebula. Beam of radiation sweeps
of radiation sweeps
round & round when poles
are not aligned with rotation
are not aligned with rotation
visual light. EE8086 – Astronomy: Stars, Galaxies & Cosmology see a pulse of light each
see pulse of light each
time the beam sweeps past
Earth Page 21 Lighthouse of the Galaxy EE8086 – Astronomy: Stars, Galaxies & Cosmology Page 22 Rotation Periods of Neutron Stars Youngest pulsars have the shortest
periods. Geometry determines
whether we see a puls...
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This document was uploaded on 11/25/2013.
- Fall '13