Objectives HR Diagram
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 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 F F 90
Energy Over a Lifetime M ~ 0.1 M sun L = 1 x 10 30 ergs/s Lifetime ~ 45 billion years Total energy over a lifetime ~ 1 x 10 48 ergs M ~ 60 M sun L = 1 x 10 40 ergs/s Lifetime ~ 1 milliion years Total energy over a lifetime ~ 1 x 10 53 ergs (10 billion * brighter) 1 supernova explosion ~ 1 x 10 54 ergs!!!
Stellar Remnants Low mass stars (M < 8M sun ) 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 of the angular momentum of the star is now in the neutron star! It spins really fast All Angular Momentum to the Neutron Star 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! Obscured F = GMm r 2 ; if m = 0; F = 0
This has been verified by the bending of light beams by the Sun and massive galaxies. Gravitational Lensing: galaxies bend around dense galaxy groups Illustration 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) = 4πR 2 * Flux = 4πR 2 * σt 4 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 O B A F G K M 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. Not enough energy to excite the electron B. Too much energy causes H to ionize C. Emitted photon can t escape the stars gravity D. Chuck Norris???
Which of the following stars contains the most hydrogen? A. A stars B. B stars C. G stars D. 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! 10 billion yrs 100 million yr MS turnoff
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) V 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