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Overview of Stellar Evolution Walter Baade 1893-1960

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Overview of Stellar Evolution Walter Baade 1893-1960 Overview of Stellar Evolution Walter Baade 1893-1960 • With Fritz Zwicky first proposed that neutron stars could be formed by supernovae in 1934 • Iron core collapse • E+p->n+ • Degenerate neutrons limit size to 3 solar masses A One Solar Mass Neutron Star is the size of Victoria • Neutron star ~10km diameter • Distance from downtown to Mt Doug • Black Hole 3km UVic- Mt. Tolmie Model of Neutron Star • Over Chandrasekhar limit of 1.4 M sun • Radius decreases 105 X to 10km so density increases 1015 X • Spin increases 1010 times so rotation from 25d to millisec Model of Neutron Star • Temperature of Millions K • Magnetic field increases 1010 to 1013 gauss (Fridge magnet ~100 g) • Convection currents in millisecs Hard to Detect Nearest Neutron Star • 180 light years • 700,000K • 20km diameter • Small luminosity • Plowing through ISM • At 200km/sec forming • A bow shock of recombining hydrogen Jocelyn Bell 1943- • Discovered pulsars in 1967 • While using new radio telescope in Cambridge UK • Discovered Crab pulsar in 1968 Pulsar Model • Rapidly rotating neutron star • Magnetic field inclined to rotation axis • Relativistic charged particles trapped by magnetic field beam light along field lines Parks’ Movie of Lighthouse Model • Neutron star rotates and beams come from magnetic axis • Spinning magnetic field generates electric field accelerating charged particles Pulsar Pulses • Spin rate = pulse periods range from 0.033 to 3.75 seconds • White Dwarf would fly apart if spun this fast • Precision equal to atomic clock implies massive object • Vela pulsar exploded ~11,000 years ago Pulsar Profiles • Pulse duration of about a millisec • Emitter must be less than 300km in size • Pulses seen at all wavelengths but most easily at radio • Sometimes strong and weak pulses • Crab pulsar on/off Crab Movie: X-Ray &Visible • Pulsar wind (like solar wind) energizes the nebula by carrying away the rotational energy of the pulsar Pulsar Glitches • Lost rotational energy observed as periods increasing • Glitch is abrupt period decrease (Vela shown in graph) • Caused by starquakes (1 cm) or fluid interior loosely coupled to crust? • Pulsars spin down in millions of years Pulsar Distribution • Thousand discovered • Millions in galaxy • Mostly in galactic plane =Milky Way • Most neutron stars not pulsars : spun down or wrong tilt • Personal point of view • Observer point of view Neutron Star in IC443 • Summer High School students • Using Chandra X-ray data • Found neutron star offset from center of SNR • Most pulsars not in remnants and lots of SN remnants have no pulsar. Why???? Why are Pulsars NOT Found in SNR? • Large proper motions • Asymmetric explosions? • Not in SNR which last ~ 50,000 years • Pulsars slow down in 10 Million years • Binary star??? Fastest Millisecond Pulsar • Spun up by mass from companion • Discovered by J. Hessels McGill • Rotates at 716 Hz = a blender • It is less than 16 km radius. • Found in Globular Cluster; old star • Figure shows pulsar ablating companion which eclipses pulsar Pulsar PSR 1257+12’s Planets • Planet masses from mutual interactions: 2 ~Earths, 1 ~moon mass • Orbit so close to pulsar they should have been destroyed in explosion Binary Pulsar PSR1913+16 • Discovered 1974; Nobel prize for Taylor&Hulse in 1993 • Orbital Period ~8 hours • One pulsar & the other a neutron star= 1.35 solar mass • Slows due to Gravitational Radiation predicted by General Relativity • Orbit shrinks 3mm/year so they will merge in 300 million years Maybe Merging Neutron Stars • ~30,000 binary neutron stars and 300 black hole binaries • 2 stars 1.4 solar masses are 30km diameter and 10km apart • This is a cut-away showing the insides Special Relativity 1905 • 1st Postulate – Observers can never detect their uniform motion except relative to other objects • 1st Postulate – Physical laws are the same for all observers • 2nd Postulate – The velocity of light is a constant and will be the same for all observers independent of their motion relative to the light source • E=Mc2 Special Relativity Time Dilation • Red & Blue make identical clocks from light pulses & mirrors • If Blue moves near the speed of light his clock runs slower relative to Red’s because his light pulses need to travel farther • Make a time machine to slow time and travel to the future Twin Paradox General Relativity 1916 • Equivalence principle: Observers cannot distinguish locally between inertial forces due to acceleration and uniform gravitational forces due to the presence of a massive body. (Light Too) Precession of Mercury’s Orbit • General Relativity theory correctly predicts the observation of the precession of Mercury’s orbit • Newtonian gravity in red is incorrect and Einstein’s in blue • A theory can not be proven correct only shown to be incorrect Gravitational Bending of Light • Positions of stars seen during a solar eclipse are displaced as predicted by General Relativity; 1919 General Relativity Time Dilation • General Relativity predicts that • Acceleration/gravity makes clock run more slowly • Seen in GPS’s • Again you can make a time machine to travel to the future Gravitational Redshift • As light climbs out of gravitational potential well it loses energy • It can not slow down so it must redshift • Has been seen for Sun, White Dwarfs and on Earth Black Hole Formation Karl Schwarzschild 1873-1916 • First solution to General Relativity equations for Black Hole • Escape velocity of : – Earth=11km/sec, – Sun=600km/sec, – white dwarf= 10,000km/sec, – neutron star= 100,000km/sec • At event horizon escape velocity =c 2 • Schwarzschild radius Rs=2GM/c • 1 Earth Mass -> 1cm • 1 Solar Mass -> 3km • Radius in km Rs=3 M in solar masses • 10 Solar Masses -> 30km Schwarzschild Radius=Event Horizon • Singularity is where R=0 F=GMm/R2 becomes infinite • Only observable properties are Mass, Charge, Rotation • If sun replaced by BH- no change in orbits Kerr Black Hole • When stars collapse they are rotating so the remnant black hole should rotate – fast • Event horizon becomes oblate spheroid • Ergosphere- area where space-time rotates with black hole Gravitational Redshift BH • As light comes out of a Black Hole it looses energy and thus redshifted • At Event Horizon light infinitely redshifted Black Hole Lens in Orion • Black hole bends light • Two images appear, one on either side Black Hole Evaporation • Black Holes do seem to radiate energy • The smaller the hole the hotter it seems – primordial ? • A 1 Solar mass black hole will last ~1070 years Falling into a Black Hole 4. Tides heat him to millions K 5. Clock A would stop as he reached event horizon 6. Person A would notice nothing unusual at event horizon Evidence for • O-type Supergiant • >3.8Msun Black Hole Black Holes: • 5.6d orbital period Cygnus X-1 • X-rays flicker in 0.01sec • 10 systems known SS433’s Jets; Black Holes are Messy Eaters • 16,000ly distant • Eclipses every 13 days • Star is 13 Msun • Interaction of magnetic fields of accretion disk and compact object ejects jets at 0.25 c • Precesses in 164 days • Seen in X-rays and radio • Black hole is 3-8 Msun Quasi-Periodic Oscillations • A mass falling into a black hole will release 100 times as much energy as could be obtained from fusion X-Ray Binary • X-ray binary containing a Black Hole will be fainter than one containing a neutron star • No terminal burst Painting of Black Hole Compton Observatory 1991-2000 • Vela 1968 designed to detect nuclear bomb tests • Beppo-Sax 1997 could pinpoint burst • SWIFT detects about 1 a day Gamma Ray Burst Animation Gamma Ray Burst Light Curves • Duration of seconds sets upper limit to size of hundreds of thousands of kilometers • Like a pulsar pulse Gamma Ray Burst Distribution • No concentration to: Sun, Sirius, Crab, galactic plane, galactic center, Andromeda galaxy, Virgo Cluster Power of Gamma Ray Bursts Brighter than all the stars in universe for a second 1053 ergs is mass of sun totally converted to energy Beaming reduces energy but increases frequency Maybe Beamed - Hypernova • Similar to core collapse supernovae but ~30 solar mass WR star • Core collapses to form Black Hole, accretion disc forms, jets form, eventually blast through surface of star, hit surrounding material, creates gamma rays GRB Effects on Earth • Nearest binary pulsar ~1600ly=104 megaTn • Occur every few hundred(?) million years Review of Black Holes & Pulsars • What happens when a star contracts? S m t • What are pulsars? How do we know they are small? • What is a Black Hole? E 3/1 • What happens if you fall into one? R t t • Why do we think they exist? 2 & X Millisecond Pulsar Top View • At the distance of the moon from the Earth the magnetic field rotates at speed of light Millisecond Pulsar Surface • Rotates at the speed of a blender Falling into BH Movie • 30 Solar Mass BH • Done by Andrew Hamilton • From 1 AU takes 65 days • No redshift X-ray Burster • Carbon (or helium) builds up on surface of neutron star • Which eventually explodes – like a nova • Illuminating disk • Observed by Dave Ballantyne with ROSSI Explorer GRB Light Echo in X-Rays • X-Rays emitted during a GRB reflect off a dust cloud 3500ly from Earth in our Galaxy • So it is beyond the dust cloud Planet and White Dwarf Orbit Millisecond Pulsar XTE 1550-56 Black Hole & Solar Mass Star.
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