Stellar Physics 10 lectures, exploring the development of
cosmology, and some of the key ideas of Big Bang theory Access PPT
slides at
http://www.astro.gla.ac.uk/users/martin/teaching/aberdeen.ppt Dr
Martin Hendry Dept of Physics and Astronomy University of Glasgow
[email protected] Slide 2 25000 10000 8000 6000 5000 4000 3000
Surface temperature (K) O5 B0 A0 F0 G0 K0 M0 M8 Luminosity (Sun=1)
Spectral Type 1 10 2 10 4 10 6 10 -2 10 -4 -10 -5 0 +5 +10 +15
Absolute Magnitude 0.001 R S 0.01 R S 0.1 R S 1 R S 10 R S Main
Sequence White dwarfs Supergiants 1000 R S 100 R S Giants We can
plot the temperature and luminosity of stars on a diagram Stars
dont appear everywhere: they group together, and most are found on
the Main Sequence Slide 3 25000 10000 8000 6000 5000 4000 3000
Surface temperature (K) O5 B0 A0 F0 G0 K0 M0 M8 Luminosity (Sun=1)
Spectral Type 1 10 2 10 4 10 6 10 -2 10 -4 -10 -5 0 +5 +10 +15
Absolute
Magnitude......................................................................................................................
Regulus Vega Sirius A AltairSun Sirius B Procyon B Barnards Star
Procyon A....... Aldebaran Mira Pollux Arcturus Rigel Deneb Antares
Betelgeuse Stars on the Main Sequence turn hydrogen into helium.
Blue stars are much hotter than the Sun, and use up their hydrogen
in a few million years Slide 4 Observational Evidence for Compact
Objects 1. White Dwarfs 2. Neutron Stars 3. Black Holes Slide 5
White Dwarfs Small but very luminous (because of high T) Can be
directly observed Slide 6 Slide 7 Slide 8 Slide 9 Slide 10
Important Type of White Dwarf for Cosmology: Type Ia Supernovae
Excellent for measuring cosmological distances good Standard Candle
Slide 11 Type Ia Supernova White dwarf star with a massive binary
companion. Accretion pushes white dwarf over the Chandrasekhar
limit, causing thermonuclear disruption Good standard candle
because:- Narrow range of luminosities at peak brightness;
Observable to very large distances Slide 12 Slide 13 Will the
Universe continue to expand forever? To find out we need to compare
the expansion rate now with the expansion rate in the distant past
Is the Universe speeding up or slowing down? Slide 14 Answer
depends on the geometry of the Universe Closed Open Flat Slide 15
We can measure this using Type Ia Supernovae Slide 16 Slide 17
Slide 18 Results: The expansion is accelerating The geometry of the
Universe is FLAT The Universe will continue to expand indefinitely
Slide 19 Cosmological Constant? Quintessence? What is driving the
cosmic acceleration? Slide 20 Neutron Stars Very much smaller:
(almost) invisible at optical, but can be seen in X-Rays if their
surfaces are very hot Slide 21 Slide 22 Crab Nebula: supernova of
1054 Slide 23 Slide 24 Slide 25 Slide 26 There exist large numbers
of compact objects in binary systems. These are powerful emitters
of X-rays, many sources are concentrated near the Galactic plane.
X-Ray Binaries: compact source orbiting a massive star Slide 27
Slide 28 Chandra (launched 1999): high-resolution X-ray map of the
Galactic Centre Chandra has revealed many more X-ray binary sources
in the Milky Way, globular clusters and external galaxies. Slide 29
XRBs: How do we get so much energy out? Need something approaching
E = mc 2 Gravitational energy from accretion Slide 30 For how long
might we expect such an X-ray binary source to shine?... Suppose we
could completely annihilate a source of, say, So if we want a
source lifetime of, say, we would need to extract around 10% of the
sources rest mass energy (same efficiency would give longer
lifetime for a less luminous source) Is this realistic? Energy
source believed to be gravitational infall (accretion) of matter
onto a neutron star from a binary companion. Energy yield / unit
mass Slide 31 Matter falls in via an accretion disk. Some orbital
angular momentum is lost by viscous friction. XRB luminosity comes
from disk as well as the central source. Slide 32 Accretion
Luminosity and the Eddington Limit If matter accretes at rate then
we expect, at radius But if is large, the accretion process becomes
self-limiting, because the emitted luminosity exerts a significant
radiation pressure force on the infalling material. Consider a
proton of mass at radius Radiation force Thomson cross-section
Slide 33 Radiation force reduces the effective gravitational force
to We can write this as where the critical, or Eddington,
luminosity is Putting in some numbers we find that which is close
to the maximum observed Slide 34 Pulsars Discovered by Jocelyn
Bell, in 1965. Slide 35 Pulsars Discovered by Jocelyn Bell, in
1965. Extremely accurate clocks Rapidly rotating NS, with beams of
radiation Slide 36 Pulsars Synchrotron radiation Slide 37 Pulsars
Observe: High spin rate High B field Electron acceleration Slide 38
Binary neutron stars Very strong gravity provides a test of GR.
Advance of periastron, Production of GWs Source of GRBs? Slide 39
Gravity in Einsteins Universe Gravity and acceleration are
completely equivalent : both cause spacetime to become curved or
warped Gravity is not a force propagating through space and time,
but the result of mass (and energy) warping spacetime itself Slide
40 Gravity in Einsteins Universe Spacetime tells matter how to
move, and matter tells spacetime how to curve Slide 41 Gravity in
Einsteins Universe v Differences between Newtonian and Einsteinian
gravity are tiny, but can be detected in the Solar System and
Einstein always wins! Slide 42 Gravity in Einsteins Universe v 1.
Precession of orbits observed for Mercury, matching GR prediction
Slide 43 Gravity in Einsteins Universe v 1. Precession of orbits
observed for Mercury, matching GR prediction 2. Bending of light
close to the Sun visible during total eclipse, measured in 1919
Slide 44 Slide 45 Slide 46 Gravity in Einsteins Universe Ultimate
case of light deflection = Black Hole: warps spacetime so much that
light cant escape Slide 47 Pressure, P Density, N.R. Electron
degeneracy pressure Rel. Electron degeneracy pressure N.R. Proton
degeneracy pressure Rel. Proton degeneracy pressure Lines of
central Pressure, constant mass A B C D E Slide 48 Evidence for
stellar black holes from binary systems: e.g. Cygnus X-1 Inferred
mass far exceeds OV limit Slide 49 Slide 50 Slide 51 Slide 52 Slide
53 Slide 54 Slide 55 Slide 56 Slide 57 Slide 58 Slide 59 Slide 60
Slide 61 Slide 62 Slide 63 Slide 64 Slide 65 Slide 66
