ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies • Homework #4 Homework #4 on Mastering Astronomy, on Mastering Astronomy, • due on Thursday due on Thursday this week, 10/08, by 5pm this week, 10/08, by 5pm • Next Extra Credit Observing Night: –Thursday, 10/08 at Sommers-Bausch
High-Mass Stars High-Mass Stars • Sequence of expansion/contraction repeats as higher and higher elements begin to fuse • Each heavier element requires higher core temperatures to fuse • Core structure keeps on building successive shell - Like an onion • Lighter elements on the outside, heavier ones on the inside
High-Mass Stars: High-Mass Stars: No significant changes in luminosity Star travels back and forth on the HR diagram In the most massive stars, changes happen so quickly that the outer layers do not have time to respond Outer layers subject to strong winds
Massive Massive red giant red giant or supergiant supergiant: : or Fierce hot Fierce hot winds and winds and pulsed ejecta ejecta pulsed Hubble Hubble
Wildest of all ! Wildest of all ! ETA CARINAE ETA CARINAE Supermassive Supermassive star (150 M SUN ) star (150 M SUN ) late in life, late in life, giant outburst giant outburst 160 yr ago 160 yr ago Violent bipolar Violent bipolar ejecta + disk + disk ejecta at equator at equator
Question: why do we see the glowing gas surrounding Question: the star to grow in time? Note: the star emitted a pulse of radiation some time ago.
Red Giant Red Giant with with intense intense brightening brightening `Light Echo’ ’ `Light Echo from pulse from pulse Star V838 Star V838 Monocerotis Monocerotis HST-ACS HST-ACS
• Most elements are formed via Helium Capture Helium Capture – A helium (2 protons) nucleus is absorbed, energy is released • The elements are created going up the periodic table in steps of 2
Other Reactions Other Reactions
Carbon (6), Oxygen (8), Neon (10) Carbon (6), Oxygen (8), Neon (10) Magnesium (12)… …. . Magnesium (12)
� E ARE STAR STUFF!! - Carl Sagan Sagan - Carl
“We are all star-stuff We are all star-stuff” ” - Carl - Carl Sagan Sagan “ • All All heavy elements are created and dispersed • through the galaxy by stars • Without high mass stars, very little very little heavier than carbon • Our atoms were once parts of stars 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 B. Silicon C. Iron D. Uranium
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 B. Silicon C. Iron D. Uranium
HIGH mass stars keep creating HIGH mass stars keep creating elements up the periodic table UNTIL… …. . elements up the periodic table UNTIL IRON (Fe, 26 protons ) (Fe, 26 protons ) IRON • Iron does not release energy through fusion or fission – Remember: Remember: All – energy created by the loss of mass from the fusion (E=mc E=mc 2 2 )
• The core of a high mass star accumulates accumulates iron as the layers iron above it fuse • Without any outward pressure, the core once again starts to contract. contract • Electron degeneracy pressure supports the core for awhile until the mass of iron gets too too heavy (how heavy?) heavy (how heavy?)
• When mass is too large (>1.4M sun ), core collapses and iron atoms get compressed into pure neutrons • protons + electrons � neutrons + neutrinos – This takes less than 0.01 seconds This takes less than 0.01 seconds – • Electron degeneracy pressure - GONE! – Core collapses completely •Eventually neutron degeneracy pressure stops the collapse abruptly •Infalling atmosphere impacts impacts on the core. •Time for a demo…
Clicker Question Clicker Question Basketball & Super ball Demo Basketball & Super ball Demo • What do you think will happen? A. The two balls will bounce up together The two balls will bounce up together A. B. The little ball will bounce higher than the The little ball will bounce higher than the B. basketball but no higher than when the little ball little ball basketball but no higher than when the is dropped alone is dropped alone C. The little ball will bounce much higher than the The little ball will bounce much higher than the C. basketball basketball
Supernova! Supernova! • The lightweight atmosphere impacts on the heavy core and is “ “bounced bounced” ” off in a huge explosion • Plus huge energy release from neutrinos! � e sta �� �� former surface zooms outwar � � former surface zooms outwar � � e sta � � i � a veloci � of 10,000 km/s! � i � a veloci � of 10,000 km/s!
“Massive Star SUPERNOVA Massive Star SUPERNOVA” ” “ • Exploding remnant Exploding remnant • of massive star massive star of disperses heavy disperses heavy elements through through elements the galaxy the galaxy • Inside may be a Inside may be a • neutron star – – a a neutron star remnant core of remnant core of pure neutrons! pure neutrons! Crab Nebula (M1), first seen as SUPERNOVA first seen as SUPERNOVA Crab Nebula (M1), on 4 July 1054 from China -- visible in daytime on 4 July 1054 from China -- visible in daytime
Was Crab SN recorded in Chaco? Was Crab SN recorded in Chaco? • Petroglyph from Chaco Canyon (New Mexico): – Correct configuration relative to the new moon for the Crab Supernovae – Of course it could also just be Venus with the moon! • Chinese records also report a “guest star” in the sky in 1054 A.D.
Observing Supernovae Observing Supernovae • About 1 per century per galaxy (none in Milky Way since (none in Milky Way since 1604) � 1604) • Bright explosions visible for weeks/months weeks/months – some visible in daytime! • Remnant visible for 100’s of thousands of years as huge bubbles and “veils”
Supernovae in Other Galaxies Supernovae in Other Galaxies • Bright enough to be seen as a sudden, bright point in other galaxies • Scores of amateur and pro astronomers monitor nearby galaxies nightly to catch them – (1 per 100 years per galaxy means that monitoring 100 galaxies will get you 1 supernova per year)
SN 1987A: Nearest One Since 1604 SN 1987A: Nearest One Since 1604 • Exploded in the Large Magellanic Cloud (companion dwarf galaxy to MW, 150,000 ly away) • Seen only from southern hemisphere – But neutrino detectors in Ohio, Japan, and Russia detected neutrinos from the explosion! • Ring structure: illuminated remnants of an earlier stellar wind or gas left over from star’s formation
Betelgeuse (In Orion) Is Currently Betelgeuse (In Orion) Is Currently In Its Red Supergiant Supergiant Phase Phase In Its Red might be next… only 1500 ly away.. would be very dramatic…
The ultimate fate of a The ultimate fate of a massive star massive star Core burns to Fe, Fe, leading to a core collapse leading to a core collapse Core burns to SUPERNOVA SUPERNOVA What happens to the Fe core? What happens to the Fe core? Neutron Star - for star masses < 30-40 M sun Neutron Star Black Hole - for star masses > 30-40 M sun Black Hole
The Stellar Graveyard The Stellar Graveyard
What’ ’s In The Stellar Graveyard? s In The Stellar Graveyard? What • Low mass stars � white dwarfs white dwarfs – Gravity vs. electron degeneracy pressure • High mass stars � neutron stars neutron stars – Gravity vs. neutron degeneracy pressure • Even more massive stars � black holes 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 B. A white dwarf C. A black hole D. A neutrino ball E. A red supergiant
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 B. A white dwarf C. A black hole D. A neutrino ball E. A red supergiant
Clicker Question Clicker Question Binary Systems: The Algol Algol Paradox Paradox Binary Systems: The • Algol Algol is a is a binary system binary system consisting of a 3.7 consisting of a 3.7 • solar mass main sequence star main sequence star and a 0.8 and a 0.8 solar mass solar mass red giant red giant. . Why is this strange? Why is this strange? solar mass • A. A. A 3.7 M Sun star should have become a red giant • before a 0.8 M Sun star • B. B. Binary stars usually have the same mass • • C. C. 0.8 M Sun stars usually never become red giants •
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