The Stellar Graveyard

Transcription

1 Life and Death of High Mass Stars (M > 8 M sun ) AST 101 Introduction to Astronomy: Stars & Galaxies Last stage: Iron core surrounded by shells of increasingly lighter elements. Announcements MIDTERM #2 on Friday, April 3 Question of the day: What Happens to the Iron Core? The Stellar Graveyard What s In The Stellar Graveyard? Low-mass stars (M < 8 M sun )! 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

2 Neutron Stars Size of a neutron star! Structure determined by gravity vs. neutron degeneracy pressure Mount Everest Neutron Star! BRONX Radius ~ 10 km Mass less than ~ 3 MSun MAN QUEENS Weight of a neutron star! Made of degenerate neutrons More massive = smaller!! BROOKLYN Crushing gravity at its surface, not a nice place to visit STATEN ISLAND Neutron star over NYC Observing the First Pulsar: BIG discovery 1.3 sec period Pinhead of! Pulsars = Rotating Neutron Stars Jocelyn Bell: Cambridge (UK) graduate student in 1967 (+Anthony Hewish) discovered pulsars by accident! Named it LGM-1 (Little Green Man) Just WHAT could cause signal? Pulsars are lighthouses in our Galaxy!

3 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 Crab Nebula SNR infrared optical radio x-ray Synchrotron Radiation Sound of Pulsars Fast electrons in strong magnetic fields! spiraling along magnetic fields Different shape (powerlaw) from thermal radiation: emits at all wavelengths, strongest in radio

4 Visible vs. X-ray emission Reading Clicker Question Thermal light from stars! visible and IR Synchrotron light from neutron stars! X-ray and radio Visible light Additional X-ray emission from hot surface (blackbody radiation) X-ray light What is a pulsar? A. A neutron star emitting pulses of light. B. A white dwarf emitting pulses of hydrogen gas. C. A red giant expanding and contracting in very short (millisecond) pulses. D. A powerful gamma ray burst. E. Your heart during final exams. Reading Clicker Question What is a pulsar? Clicker Question When a neutron star is formed, will we always see a pulsar? A. A neutron star emitting pulses of light. B. A white dwarf emitting pulses of hydrogen gas. C. A red giant expanding and contracting in very short (millisecond) pulses. D. A powerful gamma ray burst. E. Your heart during final exams. A. Yes, because due to conservation of angular momentum the neutron star will always be spinning. B. Yes, neutron stars always give off pulses of light which we can detect with sensitive enough telescopes. C. No, some neutron stars don t spin. D. No, it depends on the orientation of the neutron star s magnetic field.

5 Clicker Question When a neutron star is formed, will we always see a pulsar? A. Yes, because due to conservation of angular momentum the neutron star will always be spinning. B. Yes, neutron stars always give off pulses of light which we can detect with sensitive enough telescopes. C. No, some neutron stars don t spin. D. No, it depends on the orientation of the neutron star s magnetic field. Since white dwarfs in evolving binary systems come alive what about neutron stars? MASS TRANSFER Binary WD: Hot accretion disks, novae, supernovae Neutron star: Radiation with more vigor, no SN Neutron Stars in Binary Systems QUIZ #5 a) Describe how a Nova is produced [3pt] b) Describe how a White Dwarf Supernova is produced [3pt] c) Describe how a Massive Star Supernova is produced [3 pt] 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) d) What is the compact object left behind a low-mass star? (M< 8 M sun ) [1pt]