Download 22 Stellar Remnant/HR Diagram

HR Diagram

Objectives
Questions from Yesterday
• Centripetal Force perpendicular to the
rotation axis
• Acts to slow down collapse
• Strongest 90 deg from rotation axis
• Particles with an angle < 90 feel the collapse
more than the centripetal force outwards
• They fall into the center
F
F
• Particle collisions reduce random motions
• Each collision has a chance to send the
particle into an unstable orbit (to center)
• Or to send it into the disk
• Eventually all particles are in the disk or at
the center
F
90°
Energy Over a Lifetime

M ~ 0.1 Msun  L = 1 x 1030 ergs/s
• Lifetime ~ 45 billion years
• Total energy over a lifetime ~ 1 x 1048 ergs

M ~ 60 Msun  L = 1 x 1040 ergs/s
(10 billion * brighter)
• Lifetime ~ 1 milliion years
• Total energy over a lifetime ~ 1 x 1053 ergs

1 supernova explosion ~ 1 x 1054 ergs!!!
Stellar Remnants

Low mass stars (M < 8Msun)
• Red giant phase
• He  C and O (core)
• Thermal pulses blow off
outer layers
• Left-over core  white dwarf

White dwarfs
• Same mass as the Sun
• Same size as the Earth!!!
White Dwarfs & HR Diagram
Starting from the red giant phase…
Blows off its outer layers
Only the core is left over
Red giant
• Large radius
• High luminosity
• Fairly cool (red)
• Left over core
• Small radius (Earth)
• Low luminosity
• Really hot (blue/white)
•
•
•
•
• Overall Movement-left and down
Massive Stars
• Red Super Giant phase
• Until shell fusion can’t continue
• Core collapse  huge explosion
• Really massive
• Puff up once and collapse
Neutron Star

Density and pressure really high!  Fe turns into
protons and electrons (electrons are free)
• Neutrons have no place to move
• Slow down
• ~same energy
• Can’t occupy the same place and
energy  degeneracy

Are neutron stars bigger or smaller than white dwarfs?
A. Bigger
B. Smaller
C. Same size
All Angular Momentum to the Neutron Star
All of the angular
momentum of the
star is now in the
neutron star!
It spins really fast
“beams” charged
particles out of poles
Crab nebula:
Period ~ 0.03 seconds
Artists Conception
Crab
Nebula
Lit up the sky for a month
in 1054 AD
Has a neutron star in the
middle!
We have actually
observed this with space
based telescopes
Chandra X-ray Telescope
HST optical Telescope
Black Holes! Need General Relativity First

Einstein realized that the effects of gravity and those of an
acceleration are indistinguishable (equivalence principle)
• “force” of gravity is really
caused by the curvature
of spacetime!
•
(see special relativity for more
info on spacetime)
Spacetime

Mass curves space: Everything traveling through space follow
that curvature – Even photons!
• photons don’t have mass, under
Newtonian mechanics this should
not happen!
𝐺𝑀𝑚
𝐹 = 2 ; 𝑖𝑓 𝑚 = 0; 𝐹 = 0
𝑟
Obscured

This has been verified by the bending of light beams by
the Sun and massive galaxies.
Illustration
Gravitational Lensing: galaxies bend
around dense galaxy groups
Picture taken by Arthur Eddington
in May of 1919 during solar eclipse
- One of these stars shouldn’t be
there
• More massive things bend spacetime more
The Sun depresses spacetime
Black holes rip
through the fabric
of spacetime!!!
Nothing Escapes a Black Hole, Not Even Light!
DEMO!

A piece of fabric can simulate spacetime
Full HR Diagram
Main Sequence
 Red Supergiants – upper left
 Red giants – middle upper left
 White dwarfs – bottom left


Radius
• L (y-axis) = 4πR2 * Flux = 4πR2 * σT4
• Flux also indicates Temperature
• Temperature indicates color
• We measure color
Spectral type

Astronomers need to do better than
• “it looks blue-ish…”

Spectral classifications!
hot
cool
OBAFGKM
“Oh Be A Fine Girl/Guy and Kiss Me!”
You can make up your own
Guess why the classifications are so weird…
Assigned a letter in alphabetical
order from complex looking to
simple looking (A-Q)
 Later they figured out that these
lines were absorption lines
corresponding to different
elements
 Re-ordered according to which
elements were strong (usually H):
 OBAFGKM was born!

Why surface temp affects spectra
Strong H lines
Molecules
Can form

In the hottest spectra, Hydrogen lines begin to
disappear. This is due to
A.
B.
C.
D.
Not enough energy to excite the electron
Too much energy causes H to ionize
Emitted photon can’t escape the stars gravity
Chuck Norris???

Which of the following stars contains the most
hydrogen?
A.
B.
C.
D.
A stars
B stars
G stars
All stars contain about the same amount of hydrogen,
regardless of spectral type.
Finer Spectral Type Scale

More accurate temperatures:
• Add numbers to the letter
 Hotter
Colder
O0, O1, O2, O3, O4, O5, O6, ……., O9, B0, B1, B2, B3, etc

Higher number means cooler
• Ex. O1 star is hotter than O9
Spectroscopic Parallax?
We can now get the
temperature (within a few 10’s
of a degree)
 Find a MS star at that Temp
 Find the Luminosity/absolute
magnitude
 Gives a distance!

Distance (pc) = 10(m-M+5)/5
Star Clusters
All stars formed at the same time
 Match the shape of the main
sequence
 Compare age to MS lifetime
 Gives spectral type of MS
“turnoff” stars
 Spectral type gives absolute
magnitude!
 Yields a distance!

100 million yr
MS turnoff
10 billion yrs
V
Astronomical Filters
For lab later
 “B” filter  blue
 “V” filter  visual (green)
 “R” filter  red
 B-V  how much more blue
light than green light (color)

R
B
Telescope Lab (Friday)
You will have a telescope take images for you!!!
 Website

Pick a target
 Pick an exposure time
 PICK ALL 3 Red/Green/Blue FILTERS


You will get an email in a day or two
LT

HR diagram
• Pg 117!!!!!! finally