The Algol Paradox: A Strange Binary Star System - Prof. Rosalba Perna, Study notes of Astronomy

Download The Algol Paradox: A Strange Binary Star System - Prof. Rosalba Perna and more Study notes Astronomy in PDF only on Docsity! ASTR 1120 General Astronomy: Stars & Galaxies •Homework #4 on MA due today, by 5pm •Homework #5 on MA due Tue, March 11 • If your clicker grade on CU learn is “0” and you have been in class, please see Abhishek • Fiske planetarium public talk: “Seven Ways a Black Hole can Kill You” by Dr. Phil Plait, TONIGHT and TOMORROW,7:30pm. Binary Systems: The Algol Paradox • Algol is a binary system consisting of a 3.7 solar mass main sequence star and a 0.8 solar mass red giant. Why is this strange? • A. A 3.7 MSun star should have become a red giant before a 0.8 MSun star • B. Binary stars usually have the same mass • C. 0.8 MSun stars usually never become red giants Clicker Question What happened? • The 0.8 solar mass star once was more massive (3.0), with a 1.5 mass companion • As it became a red giant, it swelled and poured material onto its companion (lost 2.2) • The red giant (0.8) is now less massive than its companion (3.7) • Future: when the other star becomes red giant, it may pour gas back…? Binary Mass Exchange 3.0 1.5 -2.2 0.8 3.7 early MS now Moral of the story: Choose your companions wisely, for they may determine your fate Wie Stolle Sruueyid -— —_ — What’s In The Stellar Graveyard? • Lower mass stars (M<8Msun)! white dwarfs – Gravity vs. electron degeneracy pressure • High mass stars ! neutron stars – Gravity vs. neutron degeneracy pressure • Even more massive stars ! black holes – Gravity wins Novae (not Supernovae!) • Accretion of hydrogen gas onto the white dwarf can heat and fuse for while (only on surface) • Star becomes much brighter ! nova (new star) – Dimmer than supernova but still impressive! White Dwarf Supernovae • If enough mass is accreted, electron degeneracy is overcome – Limit = 1.4 Solar masses (recall the Chandrasekhar Limit) • Star then collapses, carbon fusion begins in its core (explosively) – Bye bye white dwarf! Dr. Chandrasekhar says: “Do not weigh more than 1.4 solar masses or you will collapse!” Comparing Three Types of Stellar Explosions • White Dwarf Nova – Binary systems only – Occurs in older star populations – White dwarf still survives • White Dwarf Supernova – Binary systems only – Occurs in older star populations – Nothing left inside • Massive Star Supernova – Found in young star formation regions – Make neutron stars or black holes Where is fusion happening in a white 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 Where is fusion happening in a white 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 Where is fusion happening in a 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 Neutron Stars Neutron star over NYC • Structure determined by gravity vs. neutron degeneracy pressure • Size ~ 10 km • Mass less than ~ 3 MSun • Made of degenerate neutrons – More massive = smaller !! • Crushing gravity at its surface, not a nice place to visit QUEENS BROOKLYN STATEN ISLAND BRONX MAN Observing the ‘First’ Pulsar: BIG discovery • 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? 1.3 sec period “Pulsar” = rotating neutron star Fierce magnetic fields + sizzling electrons + fast rotation ! finest “lighthouse” Thomas Gold 1968 Crab Nebula SNR infrared radio optical x-ray Pulsar Demo Neutron Star in the Lab + 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 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 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. 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. Clicker Question