Life and Deat of High Mass Stars (M > 8 Msun) Last stage: AST 101 Iron core surrounded Introduction to Astronomy: by shells of increasingly lighter elements. Stars & Galaxies “Massive Star SUPERNOVA” • When mass is too large (>1.4Msun), core collapses and iron atoms get compressed into • Exploding remnant pure neutrons of massive star disperses heavy • protons + electrons ! neutrons elements through + neutrinos the galaxy • Eventually neutron degeneracy pressure stops the collapse abruptly • Inside may be a neutron star – a • Infalling atmosphere impacts on the core and remnant core of bounces back [recall demo from last class] pure neutrons! Te stars former surface zooms outward ( Crab Nebula (M1), first seen as SUPERNOVA wit a velocit of 10,000 km/s! on 4 July 1054 from China -- visible in daytime Observing Supernovae Was Crab SN recorded in Chaco? • About 1 per century per galaxy • Petroglyph from (none in Milky Way since Chaco Canyon (New 1604) " Mexico): – Correct configuration • Bright explosions visible for relative to the new weeks/months moon for the Crab – some visible in daytime! Supernovae – Of course it could also • Remnant visible for 100 s of just be Venus with the ’ moon! thousands of years as huge bubbles and “veils” • Chinese records also report a “guest star” in the sky in 1054 A.D. Supernovae in Other Galaxies SN 1987A: Nearest One Since 1604 • Exploded in the Large • Bright enough to be seen Magellanic Cloud as a sudden, bright point (companion dwarf galaxy in other galaxies to MW, 150,000 ly away) • Scores of amateur and • Seen only from southern hemisphere pro astronomers monitor – But neutrino detectors in nearby galaxies nightly to Ohio, Japan, and Russia catch them detected neutrinos from the explosion! – (1 per 100 years per galaxy means that monitoring 100 galaxies will get you 1 • Ring structure: illuminated supernova per year) remnants of an earlier stellar wind or gas left over from star’s formation Betelgeuse (In Orion) Is Currently The ultimate fate of a In Its Red Supergiant Phase massive star Core burns to Fe, leading to a core collapse SUPERNOVA might be next… only 1500 ly What happens to the Fe core? away.. would be very dramatic… Neutron Star - for star masses < 30-40 Msun Black Hole - for star masses > 30-40 Msun The Stellar Graveyard What’s In The Stellar Graveyard? • Low mass stars ! 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 Clicker Question Clicker Question When a high-mass star (M>8Msun)ends its When a high-mass star (M>8Msun)ends its life, what does it leave behind? life, what does it leave behind? A. A neutron star or black hole A. A neutron star or black hole B. A white dwarf B. A white dwarf C. A black hole C. A black hole D. A neutrino ball D. A neutrino ball E. A red supergiant E. A red supergiant Clicker Question Clicker Question Binary Systems: The Algol Paradox Binary Systems: The Algol Paradox • Algol is a binary system consisting of a 3.7 • Algol is a binary system consisting of a 3.7 solar mass main sequence star and a 0.8 solar mass main sequence star and a 0.8 solar mass red giant. Why is this strange? solar mass red giant. Why is this strange? • A. A 3.7 MSun star should have become a red giant • A. A 3.7 MSun star should have become a red giant before a 0.8 MSun star before a 0.8 MSun star • B. Binary stars usually have the same mass • B. Binary stars usually have the same mass • C. 0.8 MSun stars usually never become red giants • C. 0.8 MSun stars usually never become red giants What happened? early MS Algol Binary System Binary Mass Exchange 3.0 1.5 • Binary stars can • The 0.8 solar mass star once was more massive (3.0), with have different a 1.5 mass companion -2.2 masses but usually ARE formed at the • As it became a red giant, it same time. swelled and poured material onto its companion (lost 2.2) now • More massive star • The red giant (0.8) is now 0.8 3.7 less massive than its should have had a companion (3.7) shorter main sequence lifetime • Future: when the other star becomes red giant, it may pour gas back…? Moral of the story: Choose your companions wisely, for they may determine your fate Novae White Dwarfs in Binary (not Supernovae!) Systems • Accretion of hydrogen • Mass transfer from a gas onto the white companion red giant dwarf can heat and spirals into an fuse into helium for a accretion disk while (only on surface) • Inner parts become VERY hot; glow in • Star becomes much UV (mostly), X-rays brighter ! nova (new star) – Dimmer than supernova but still impressive! White Dwarf Supernovae Comparing The Two Types of Supernovae • If enough mass is • Massive star SN (collapse of massive star) accreted, electron – Found in young star formation regions degeneracy is – Make neutron stars or black holes overcome – Limit = 1.4 Solar • White dwarf SN (flash burning of WD) masses (recall the – Binary systems only Chandrasekhar Limit) – Occurs in older star populations • Star then collapses, carbon fusion begins in – Nothing left inside its core (explosively) Dr. Chandrasekhar says: Do not weigh more than We’ll be looking at these again as – Bye bye white dwarf! 1.4 solar masses or you will collapse! distance measurement tools! Review Clicker Question Comparing Three Types of Stellar Explosions Where is fusion happening in a nova? • White Dwarf Nova – Binary systems only – Occurs in older star populations A. In the core, carbon is being fused into – White dwarf still survives heavier elements. • White Dwarf Supernova – Binary systems only B. On the surface, hydrogen is being fused – Occurs in older star populations into helium. – Nothing left inside C. No fusion occurs in a nova, the light • Massive Star Supernova comes from the collapse (and bounce) – Found in young star formation regions of the star. – Make neutron stars or black holes Clicker Question Clicker Question Where is fusion happening in a white Where is fusion happening in a nova? 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 nova, the light C. No fusion occurs in a white dwarf comes from the collapse (and bounce) supernova, the light comes from the of the star. collapse (and bounce) of the star. Clicker Question Clicker Question Where is fusion happening in a white Where is fusion happening in a dwarf 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 white dwarf 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. 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. .