Life of a Low-Mass Star REVIEW
END STATE: AST 101 PLANETARY NEBULA Introduction to Astronomy: + Stars & Galaxies WHITE DWARF
Planetary Nebulae – White dwarfs WHAS IS A WHITE DWARF?
Exposed core of a low-mass star that has died
Mostly made of Carbon and Oxygen
No fusion to maintain heat and pressure to balance gravity pull Electron degeneracy pressure balances inward crush of its own gravity
Very high density and hence gravity
Maximum mass=1.4 Msun (Chandrasekar limit) Funky properties of white dwarf material! Size Of A White Dwarf
Size of Earth 1 Kg chocolate cake! 2 Kg chocolate cake!
0.8 Msun white dwarf! 0.4 Msun white dwarf!
Clicker Question Which is correct order for some
• Hubble Space stages of life in a low-mass star? Telescope spies A. protostar, main-sequence star, red giant, 12-13 billion year planetary nebula, white dwarf old white dwarfs – Formed less than B. protostar, main-sequence star, red giant, 1 billion years supernova, neutron star after the creation of the universe C. main-sequence star, white dwarf, red giant, planetary nebula, protostar D. protostar, main-sequence star, planetary nebula, red giant E. protostar, red giant, main-sequence star, © HST and H. Richer (University of British planetary nebula, white dwarf Columbia) Clicker Question Time scales for Evolution Which is correct order for some of Sun-like Star stages of life in a low-mass star? H core burning Main Sequence 1010 yr 10 billion years A. protostar, main-sequence star, red giant, Inactive He core, H shell burning Red Giant 108 yr planetary nebula, white dwarf 100 million years B. protostar, main-sequence star, red giant, He core burning (unstable), ” Helium Flash Hours supernova, neutron star He core burning (stable), ” Horizontal Branch 107 yr C. main-sequence star, white dwarf, red giant, 10 million years planetary nebula, protostar C core, He + H shells burning Bright Red Giant 104 yr D. protostar, main-sequence star, planetary 10 thousand years nebula, red giant Envelope ejected Planetary Nebula 105 yr E. protostar, red giant, main-sequence star, 100 thousand years planetary nebula, white dwarf Cooling C/O core White Dwarf - Cold C/O core Black Dwarf ∞
Sirius A & B Clicker Question Main Sequence & White Dwarf The Big Bang produced only hydrogen and
Chandra image, X-ray light helium. Suppose the universe contained only low mass stars. Would elements heavier than Carbon and Oxygen exist? A. Yes B. No
Hubble image, visible light Clicker Question Lives of Intermediate/High-Mass The Big Bang produced only hydrogen and Stars helium. Suppose the universe contained • Low mass: < 2 times the Sun only low mass stars. Would elements heavier than Carbon and Oxygen exist? • Intermediate mass: 2-8 times the Sun A. Yes B. No • High mass: > 8 times the Sun
General Principles Are the Same: Battle Between Pressure and Gravity Intermediate-Mass Stars
• Main sequence • May burn up to carbon but do not have enough mass lifetimes are much to get temperatures high enough to go any higher up shorter the periodic table
• Early stages after • Degeneracy pressure stops the core from collapsing main sequence and heating enough: particles are squashed together – Similar to a low mass as much as possible star, but happen much
faster • No helium flash • End their lives with planetary nebulae, white dwarfs, similarly to low-mass stars. High-Mass Stars (M >8 MSUN) • Most elements are formed via Helium Capture • Sequence of expansion/contraction – A helium (2 protons) nucleus is absorbed, energy is repeats as higher and higher released elements begin to fuse • The elements are created going up the periodic • Each heavier element requires table in steps of 2 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
Carbon (6), Oxygen (8), Neon (10) Other Reactions Magnesium (12)…. “WE ARE ALL STAR STUFF!” - Carl Sagan “We are all star-stuff” • All heavy elements are created and dispersed through the galaxy by stars
• Without high mass stars, no heavy elements
• 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
HIGH mass stars keep creating elements up the period table UNTIL…. IRON (Fe, 26 protons ) There Is No Way Iron Can Produce Any Energy to Push Back Against the Crush • Iron does not release energy of Gravity in the Star’s Core through fusion or fission The star is DOOMED!!! – Remember: All energy created by the loss of mass from the fusion or the fission (E=mc2) 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
Massive No significant changes red giant in luminosity or supergiant: Star travels back and forth on the HR diagram Fierce hot winds and In the most massive stars, changes happen so quickly pulsed ejecta that the outer layers do not have time to respond
Outer layers subject to strong winds Hubble Question: why do we see the glowing gas surrounding Wildest of all ! the star to grow in time?
ETA CARINAE
Supermassive star (150 MSUN ) 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
Red Giant • The core of a high with mass star accumulates intense iron as the layers brightening above it fuse
`Light Echo • Without any outward pressure, the core from pulse once again starts to contract.
• Electron degeneracy Star V838 pressure supports the Monocerotis core for awhile until the HST-ACS mass of iron gets too heavy (how heavy?) • When mass is too large Big and small balls Demo (>1.4Msun), core collapses and iron atoms get compressed into pure neutrons • What do you think will happen? • protons + electrons ! neutrons + neutrinos A. The little ball will bounce up together with the – This takes less than 0.01 seconds others • Electron degeneracy pressure - GONE! – Core collapses completely B. The little ball will bounce higher than the others, but no higher than when the little ball is dropped • Eventually neutron degeneracy pressure stops the alone collapse abruptly
• Infalling atmosphere impacts on the core. C. The little ball will bounce much higher than the • Time for a demo… other balls
Supernova!
• The lightweight atmosphere impacts on the heavy core and is “bounced” off in a huge explosion
• Plus huge energy release from neutrinos!
Te star s former surface zooms outward wit a velocit of 10,000 km/s!