ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars - PowerPoint PPT Presentation

ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies •Homework Homework #4 on MA due today, by 5pm #4 on MA due today, by 5pm • •Homework #5 on MA due Tue, Homework #5 on MA due Tue, 10/20, by 5pm. 10/20, by 5pm. • • If your clicker grade on CU learn is If your clicker grade on CU learn is “ “0 0” ” and and • you have been in class, please you have been in class, please e-mail us your e-mail us your Clicker ID Clicker ID SECOND MIDTERM THURSDAY 10/15 SECOND MIDTERM THURSDAY 10/15

Review Comparing Three Types of Stellar Comparing Three Types of Stellar Explosions Explosions • White White Dwarf Nova Dwarf Nova • – Binary systems only Binary systems only – – Occurs in older star populations Occurs in older star populations – – White dwarf White dwarf still survives still survives – • White Dwarf Supernova White Dwarf Supernova • – Binary systems only Binary systems only – – Occurs in older star populations Occurs in older star populations – – Nothing left inside Nothing left inside – • Massive Star Supernova Massive Star Supernova • – Found in young star formation regions Found in young star formation regions – – Make neutron stars or black holes Make neutron stars or black holes –

Clicker Question Clicker Question Where is fusion happening in a nova nova? ? Where is fusion happening in a A. In the core, carbon is being fused into heavier elements. B. On the surface, hydrogen is being fused into helium. C. No fusion occurs in a nova, the light comes from the collapse (and bounce) of the star.

Clicker Question Clicker Question Where is fusion happening in a nova nova? ? Where is fusion happening in a A. In the core, carbon is being fused into heavier elements. B. On the surface, hydrogen is being fused into helium. C. No fusion occurs in a nova, the light comes from the collapse (and bounce) of the star.

Clicker Question Clicker Question Where is fusion happening in a white white Where is fusion happening in a dwarf supernova? ? dwarf supernova A. In the core, carbon is being fused into heavier elements. B. On the surface, hydrogen is being fused into helium. C. No fusion occurs in a white dwarf supernova, the light comes from the collapse (and bounce) of the star.

Clicker Question Clicker Question Where is fusion happening in a white white Where is fusion happening in a dwarf supernova? ? dwarf supernova A. In the core, carbon is being fused into heavier elements. B. On the surface, hydrogen is being fused into helium. C. No fusion occurs in a white dwarf supernova, the light comes from the 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 heavier elements. B. On the surface, hydrogen is being fused into helium. C. No fusion occurs in a massive star supernova, the light comes from the 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 heavier elements. B. On the surface, hydrogen is being fused into helium. C. No fusion occurs in a massive star supernova, the light comes from the collapse (and bounce) of the star.

The Stellar Graveyard The Stellar Graveyard

What’ ’s In The Stellar Graveyard? s In The Stellar Graveyard? What • Lower mass stars � white dwarfs – Gravity vs. electron degeneracy pressure • High mass stars High mass stars (M>8M � � • ) (M>8M sun but M<30-40M sun sun but M<30-40M sun ) neutron stars neutron stars – Gravity vs. neutron degeneracy pressure • Even more massive stars � black holes – Gravity wins

Neutron Stars Neutron Stars • Structure determined by • Structure determined by gravity vs. neutron gravity vs. neutron degeneracy pressure degeneracy pressure BRONX BRONX • Radius ~ 10 km • Radius ~ 10 km • Mass less than ~ 3 less than ~ 3 M M Sun • Mass Sun MAN MAN QUEENS QUEENS • Made of degenerate • Made of degenerate neutrons neutrons – More massive = smaller !! More massive = smaller !! – BROOKLYN BROOKLYN • Crushing gravity at its • Crushing gravity at its STATEN STATEN surface, not a nice place ISLAND surface, not a nice place ISLAND to visit to visit Neutron star over NYC

Size of a neutron star Mount Everest Neutron Star Weight of a neutron star Pinhead of

Observing the ‘ ‘First First’ ’ Pulsar: Pulsar: BIG discovery BIG discovery Observing the 1.3 sec period 1.3 sec period • Jocelyn Bell: : • Jocelyn Bell Cambridge (UK) Cambridge (UK) graduate student in graduate student in 1967 (+ (+Anthony Anthony 1967 Hewish) ) discovered discovered Hewish pulsars by accident! accident! pulsars by • Named it LGM-1 (Little • Named it LGM-1 (Little Green Man) Just Just Green Man) WHAT could cause WHAT could cause signal? ? signal

“Pulsar Pulsar” ” “ = rotating = rotating neutron star neutron star Fierce magnetic fields Fierce magnetic fields + sizzling electrons + sizzling electrons + fast rotation + fast rotation � finest finest “ “lighthouse lighthouse” ” � Thomas Gold 1968 Thomas Gold 1968

Pulsars and Neutron Stars Pulsars and Neutron Stars Pulsars are lighthouses Pulsars are lighthouses in our Galaxy! in our Galaxy!

Pulsars often discovered Pulsars often discovered in supernova remnants. in supernova remnants. The Crab Nebula (known The Crab Nebula (known to be supernova remnant) to be supernova remnant) Is a well known example. Is a well known example. The Crab pulsar also The Crab pulsar also pulses in visual light pulses in visual light

Crab Crab Nebula Nebula SNR SNR optical optical infrared infrared x-ray x-ray radio radio

Pulsar Demo Pulsar Demo Neutron Star in the Lab Neutron Star in the Lab + Sound of Pulsars + Sound of Pulsars

Synchrotron Radiation Synchrotron Radiation • Fast electrons in Fast electrons in • strong magnetic strong magnetic fields � fields � spiraling along along spiraling magnetic fields magnetic fields • Different shape Different shape • (powerlaw powerlaw) from ) from ( thermal radiation: thermal radiation: emits at all all emits at wavelengths, wavelengths, strongest in radio strongest in radio

Visible vs. X-ray emission Visible vs. X-ray emission Visible light Visible light • Thermal light Thermal light • from stars stars � � from visible and IR visible and IR X-ray light X-ray light • Synchrotron light Synchrotron light • from neutron neutron from stars � � X-ray X-ray stars and radio and radio

Reading Clicker Question Clicker Question Reading What is a pulsar? 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 Clicker Question Reading What is a pulsar? 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.

Clicker Question Clicker Question When a neutron star is formed, will we When a neutron star is formed, will we always see a pulsar? 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.

Clicker Question Clicker Question When a neutron star is formed, will we When a neutron star is formed, will we always see a pulsar? 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 Since white dwarfs in evolving binary systems come “ “alive alive” ” – – what about what about neutron stars neutron stars? ? come Binary WD: : Binary WD Hot accretion Hot accretion disks, novae, disks, novae, supernovae supernovae Neutron star: : Neutron star Radiation with Radiation with more vigor, more vigor, no SN no SN MASS TRANSFER MASS TRANSFER