High-Mass Stars General Astronomy: Sequence of - PowerPoint PPT Presentation

ASTR 1120 High-Mass Stars General Astronomy: • Sequence of expansion/contraction Stars & Galaxies repeats as higher and higher elements begin to fuse • Each heavier element requires higher core temperatures to fuse • Core structure • Homework #4 on Mastering Astronomy, keeps on building due on Thursday this week, 10/08, by 5pm successive shell - Like an onion • Next Extra Credit Observing Night: • Lighter elements on the outside, –Thursday, 10/08 at Sommers-Bausch heavier ones on the inside High-Mass Stars: Massive red giant or supergiant: No significant changes in luminosity Fierce hot Star travels back and forth winds and on the HR diagram pulsed ejecta In the most massive stars, changes happen so quickly that the outer layers do not have time to respond Outer layers subject Hubble to strong winds

Question: why do we see the glowing gas surrounding Wildest of all ! the star to grow in time? ETA CARINAE Supermassive star (150 M SUN ) Note: the star emitted a late in life, pulse of radiation some giant outburst time ago. 160 yr ago Violent bipolar ejecta + disk at equator • Most elements are formed via Helium Capture Red Giant with – A helium (2 protons) nucleus is absorbed, energy is released intense • The elements are created going up the periodic brightening table in steps of 2 `Light Echo’ from pulse Star V838 Monocerotis HST-ACS

Carbon (6), Oxygen (8), Neon (10) Other Reactions Magnesium (12)…. � E ARE STAR STUFF!! “We are all star-stuff” - Carl Sagan - Carl Sagan • All heavy elements are created and dispersed through the galaxy by stars • Without high mass stars, very little heavier than carbon • Our atoms were once parts of stars that died more than 4.6 billion years ago, whose remains were swept up into the solar system when the Sun formed

Clicker Question Clicker Question What is the heaviest element that can be What is the heaviest element that can be created through fusion? created through fusion? A. Carbon A. Carbon B. Silicon B. Silicon C. Iron C. Iron D. Uranium D. Uranium HIGH mass stars keep creating • The core of a high elements up the periodic table UNTIL…. mass star accumulates IRON (Fe, 26 protons ) iron as the layers above it fuse • Iron does not release energy • Without any outward pressure, the core through fusion or once again starts to fission contract. – Remember: All energy created by the loss of mass • Electron degeneracy from the fusion pressure supports the (E=mc 2 ) core for awhile until the mass of iron gets too heavy (how heavy?)

Clicker Question • When mass is too large (>1.4M sun ), core collapses and Basketball & Super ball Demo iron atoms get compressed into pure neutrons • What do you think will happen? • protons + electrons � neutrons + neutrinos – This takes less than 0.01 seconds A. The two balls will bounce up together • Electron degeneracy pressure - GONE! – Core collapses completely B. The little ball will bounce higher than the basketball but no higher than when the little ball •Eventually neutron degeneracy pressure stops the is dropped alone collapse abruptly •Infalling atmosphere impacts on the core. C. The little ball will bounce much higher than the •Time for a demo… basketball “Massive Star SUPERNOVA” Supernova! • Exploding remnant of massive star • The lightweight atmosphere impacts on disperses heavy elements through the heavy core and is “bounced” off in the galaxy a huge explosion • Inside may be a • Plus huge energy release from neutron star – a neutrinos! remnant core of pure neutrons! � e sta ��� former surface zooms outwar � � i � a veloci � of 10,000 km/s! Crab Nebula (M1), first seen as SUPERNOVA on 4 July 1054 from China -- visible in daytime

Observing Supernovae Was Crab SN recorded in Chaco? • About 1 per century per galaxy (none in Milky Way since • Petroglyph from 1604) � Chaco Canyon (New Mexico): • Bright explosions visible for – Correct configuration weeks/months relative to the new 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 thousands of years as huge moon! 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 Magellanic Cloud • Bright enough to be seen (companion dwarf galaxy as a sudden, bright point to MW, 150,000 ly away) in other galaxies • Seen only from southern • Scores of amateur and 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

The ultimate fate of a Betelgeuse (In Orion) Is Currently In Its Red Supergiant Phase massive star Core burns to Fe, leading to a core collapse SUPERNOVA might be next… What happens to the Fe core? only 1500 ly away.. would be Neutron Star - for star masses < 30-40 M sun very dramatic… Black Hole - for star masses > 30-40 M sun 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>8M sun )ends its When a high-mass star (M>8M sun )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 M Sun star should have become a red giant • A. A 3.7 M Sun star should have become a red giant before a 0.8 M Sun star before a 0.8 M Sun star • B. Binary stars usually have the same mass • B. Binary stars usually have the same mass • C. 0.8 M Sun stars usually never become red giants • C. 0.8 M Sun stars usually never become red giants

What happened? early MS Algol Binary System Binary Mass Exchange 1.5 3.0 • Binary stars can • The 0.8 solar mass star once was more massive (3.0), with have different -2.2 a 1.5 mass companion masses but usually ARE formed at the • As it became a red giant, it swelled and poured material same time. onto its companion (lost 2.2) now 0.8 • The red giant (0.8) is now 3.7 • More massive star less massive than its should have had a companion (3.7) shorter main • Future: when the other star sequence lifetime becomes red giant, it may pour gas back…? Moral of the story: Choose your companions wisely, for they may determine your fate White Dwarfs in Binary White Dwarfs: summary Systems • For <8 M Sun star = a hot core of carbon • Mass transfer from a (can also be oxygen for higher mass stars) companion red giant spirals into an accretion disk Size ~ Earth !! Density – 1 cm 3 is about 5 tons Held up by electron degeneracy pressure • Inner parts become VERY hot; glow in UV (mostly), X-rays Cool from white-blue through red to black Maximum mass = 1.4 M sun

Novae White Dwarf Supernovae (not Supernovae!) • If enough mass is • Accretion of hydrogen accreted, electron gas onto the white degeneracy is dwarf can heat and overcome fuse for while (only on surface) – Limit = 1.4 Solar masses (recall the Chandrasekhar Limit) • Star becomes much • Star then collapses, brighter � nova (new carbon fusion begins in star) its core (explosively) – Dimmer than Dr. Chandrasekhar says: supernova but still “Do not weigh more than – Bye bye white dwarf! 1.4 solar masses or you impressive! will collapse!” Comparing The Two Types of Supernovae • Massive star SN (collapse of massive star) – Found in young star formation regions – Make neutron stars or black holes • White dwarf SN (flash burning of WD) – Binary systems only – Occurs in older star populations – Nothing left inside We’ll be looking at these again as distance measurement tools!