ASTR 1120 Review Comparing Three Types of Stellar General Astronomy: Explosions Stars & Galaxies • White Dwarf Nova – Binary systems only •Homework #4 on MA due today, by 5pm – Occurs in older star populations •Homework #5 on MA due Tue, 10/20, by 5pm. – White dwarf still survives • White Dwarf Supernova – Binary systems only • If your clicker grade on CU learn is “0” and – Occurs in older star populations you have been in class, please e-mail us your – Nothing left inside • Massive Star Supernova Clicker ID – Found in young star formation regions – Make neutron stars or black holes SECOND MIDTERM THURSDAY 10/15 Clicker Question Clicker Question Where is fusion happening in a nova? Where is fusion happening in a nova? A. In the core, carbon is being fused into A. In the core, carbon is being fused into heavier elements. heavier elements. B. On the surface, hydrogen is being fused B. On the surface, hydrogen is being fused into helium. into helium. C. No fusion occurs in a nova, the light C. No fusion occurs in a nova, the light comes from the collapse (and bounce) comes from the collapse (and bounce) of the star. of the star.
Clicker Question Clicker Question Where is fusion happening in a white Where is fusion happening in a white dwarf supernova? dwarf supernova? A. In the core, carbon is being fused into A. In the core, carbon is being fused into heavier elements. heavier elements. B. On the surface, hydrogen is being fused B. On the surface, hydrogen is being fused into helium. into helium. C. No fusion occurs in a white dwarf C. No fusion occurs in a white dwarf supernova, the light comes from the supernova, the light comes from the collapse (and bounce) of the star. collapse (and bounce) of the star. Clicker Question Clicker Question Where is fusion happening in a Where is fusion happening in a massive star supernova? massive star supernova? A. In the core, carbon is being fused into A. In the core, carbon is being fused into heavier elements. heavier elements. B. On the surface, hydrogen is being fused B. On the surface, hydrogen is being fused into helium. into helium. C. No fusion occurs in a massive star C. No fusion occurs in a massive star supernova, the light comes from the supernova, the light comes from the collapse (and bounce) of the star. collapse (and bounce) of the star.
The Stellar Graveyard What’s In The Stellar Graveyard? • Lower mass stars � white dwarfs – Gravity vs. electron degeneracy pressure • High mass stars (M>8M sun but M<30-40M sun ) � neutron stars – Gravity vs. neutron degeneracy pressure • Even more massive stars � black holes – Gravity wins Neutron Stars Size of a neutron star • Structure determined by gravity vs. neutron Mount Everest Neutron Star degeneracy pressure BRONX • Radius ~ 10 km • Mass less than ~ 3 M Sun MAN QUEENS Weight of a neutron star • Made of degenerate neutrons – More massive = smaller !! BROOKLYN • Crushing gravity at its STATEN ISLAND surface, not a nice place to visit Pinhead of Neutron star over NYC
Observing the ‘First’ Pulsar: BIG discovery “Pulsar” 1.3 sec period = rotating neutron star • Jocelyn Bell: Fierce magnetic fields Cambridge (UK) + sizzling electrons graduate student in + fast rotation 1967 (+Anthony � finest “lighthouse” Hewish) discovered pulsars by accident! • Named it LGM-1 (Little Green Man) Just WHAT could cause Thomas Gold 1968 signal? Pulsars and Neutron Stars Pulsars often discovered in supernova remnants. The Crab Nebula (known to be supernova remnant) Is a well known example. The Crab pulsar also pulses in visual light Pulsars are lighthouses in our Galaxy!
Crab Nebula SNR Pulsar Demo optical infrared Neutron Star in the Lab x-ray radio + Sound of Pulsars Synchrotron Radiation • Fast electrons in strong magnetic fields � spiraling along magnetic fields • Different shape (powerlaw) from thermal radiation: emits at all wavelengths, strongest in radio
Reading Clicker Question Visible vs. X-ray emission What is a pulsar? Visible light • Thermal light from stars � visible and IR A. A neutron star emitting pulses of light. B. A white dwarf emitting pulses of X-ray light • Synchrotron light hydrogen gas. from neutron C. A red giant expanding and contracting stars � X-ray in very short (millisecond) pulses. and radio D. A powerful gamma ray burst. E. Your heart during final exams. Reading Clicker Question Clicker Question When a neutron star is formed, will we What is a pulsar? always see a pulsar? A. Yes, because due to conservation of angular A. A neutron star emitting pulses of light. momentum the neutron star will always be B. A white dwarf emitting pulses of spinning. hydrogen gas. B. Yes, neutron stars always give off pulses of C. A red giant expanding and contracting light which we can detect with sensitive in very short (millisecond) pulses. enough telescopes. D. A powerful gamma ray burst. C. No, some neutron stars don’t spin. E. Your heart during final exams. D. No, it depends on the orientation of the neutron star’s magnetic field.
Clicker Question Since white dwarfs in evolving binary systems come “alive” – what about neutron stars? When a neutron star is formed, will we always see a pulsar? Binary WD: Hot accretion A. Yes, because due to conservation of angular disks, novae, momentum the neutron star will always be supernovae spinning. B. Yes, neutron stars always give off pulses of Neutron star: Radiation with light which we can detect with sensitive more vigor, enough telescopes. no SN C. No, some neutron stars don’t spin. MASS TRANSFER D. No, it depends on the orientation of the neutron star’s magnetic field. Neutron Stars in Binary Systems If white dwarfs can do it, so can neutron stars! • Mass transfer builds very hot accretion disk around neutron star: � intense x-ray emission (continuosly) from disk � explosive helium burning (in bursts) on NS = X-ray Burster � matter falling in can “spin up” the neutron star (or pulsar)
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