AST 101 PLANETARY NEBULA Introduction to … 101 Introduction to Astronomy: Stars & Galaxies Life of...
Transcript of AST 101 PLANETARY NEBULA Introduction to … 101 Introduction to Astronomy: Stars & Galaxies Life of...
AST 101 Introduction to Astronomy:
Stars & Galaxies
Life of a Low-Mass Star REVIEW
END STATE: PLANETARY NEBULA + WHITE DWARF
Planetary Nebulae – White dwarfs WHAS IS A WHITE DWARF?
Exposed core of a low-mass star that has died
No fusion to maintain heat and pressure to balance gravity pull Electron degeneracy pressure balances inward crush of its own gravity
Mostly made of Carbon and Oxygen
Very high density and hence gravity
Maximum mass=1.4 Msun (Chandrasekar limit)
Size Of A White Dwarf Size of Earth
Funky properties of white dwarf material!
1 Kg chocolate cake!
2 Kg chocolate cake!
0.4 Msun white dwarf!0.8 Msun white dwarf!
• Hubble Space Telescope spies 12-13 billion year old white dwarfs – Formed less than
1 billion years after the creation of the universe
© HST and H. Richer (University of British Columbia)
Which is correct order for some stages of life in a low-mass star? A. protostar, main-sequence star, red giant,
planetary nebula, white dwarf B. protostar, main-sequence star, red giant,
supernova, neutron star 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,
planetary nebula, white dwarf
Clicker Question
Which is correct order for some stages of life in a low-mass star? A. protostar, main-sequence star, red giant,
planetary nebula, white dwarf B. protostar, main-sequence star, red giant,
supernova, neutron star 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,
planetary nebula, white dwarf
Clicker Question Time scales for Evolution of Sun-like Star
H core burning Main Sequence 1010 yr 10 billion years
Inactive He core, H shell burning Red Giant 108 yr 100 million years
He core burning (unstable), ” Helium Flash Hours He core burning (stable), ” Horizontal Branch 107 yr
10 million years C core, He + H shells burning Bright Red Giant 104 yr
10 thousand years Envelope ejected Planetary Nebula 105 yr
100 thousand years Cooling C/O core White Dwarf - Cold C/O core Black Dwarf ∞
Hubble image, visible light
Chandra image, X-ray light
Sirius A & B Main Sequence & White Dwarf
The Big Bang produced only hydrogen and helium. Suppose the universe contained
only low mass stars. Would elements heavier than Carbon and Oxygen exist?
A. Yes B. No
Clicker Question
The Big Bang produced only hydrogen and helium. Suppose the universe contained
only low mass stars. Would elements heavier than Carbon and Oxygen exist?
A. Yes B. No
Clicker Question Lives of Intermediate/High-Mass
Stars • Low mass: < 2 times the Sun
• Intermediate mass: 2-8 times the Sun
• High mass: > 8 times the Sun
General Principles Are the Same: Battle Between Pressure and Gravity
• Main sequence lifetimes are much shorter
• Early stages after
main sequence – Similar to a low mass
star, but happen much faster
• No helium flash
Intermediate-Mass Stars
• May burn up to carbon but do not have enough mass to get temperatures high enough to go any higher up the periodic table
• Degeneracy pressure stops the core from collapsing and heating enough: particles are squashed together as much as possible
• End their lives with planetary nebulae, white dwarfs, similarly to low-mass stars.
• Sequence of expansion/contraction repeats as higher and higher elements begin to fuse
• Each heavier element requires higher core temperatures to fuse
High-Mass Stars (M >8 MSUN)
• Core structure keeps on building successive shell - Like an onion • Lighter elements on the outside, heavier ones on the inside
• Most elements are formed via 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 Carbon (6), Oxygen (8), Neon (10)
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 )
• Iron does not release energy through fusion or fission – Remember: All
energy created by the loss of mass from the fusion or
the fission (E=mc2)
There Is No Way Iron Can Produce Any Energy to Push Back Against the Crush
of Gravity in the Star’s Core
The star is DOOMED!!!
What is the heaviest element that can be created through fusion?
A. Carbon B. Silicon C. Iron D. Uranium
Clicker Question
What is the heaviest element that can be created through fusion?
A. Carbon B. Silicon C. Iron D. Uranium
Clicker Question
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 red giant or supergiant: Fierce hot winds and pulsed ejecta
Hubble
Wildest of all ! ETA CARINAE Supermassive star (150 MSUN ) late in life, giant outburst 160 yr ago
Violent bipolar ejecta + disk at equator
Question: why do we see the glowing gas surrounding the star to grow in time?
Note: the star emitted a pulse of radiation some time ago.
Star V838 Monocerotis HST-ACS
`Light Echo� from pulse
Red Giant with intense brightening
• The core of a high mass star accumulates iron as the layers above it fuse
• Without any outward pressure, the core once again starts to contract.
• Electron degeneracy pressure supports the core for awhile until the mass of iron gets too heavy (how heavy?)
• When mass is too large (>1.4Msun), core collapses and iron atoms get compressed into pure neutrons
• protons + electrons ! neutrons + neutrinos – 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 on the core.
• Time for a demo…
Big and small balls Demo
• What do you think will happen?
A. The little ball will bounce up together with the others
B. The little ball will bounce higher than the others, but no higher than when the little ball is dropped alone
C. The little ball will bounce much higher than the 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!
The star�s former surface zooms outward ��� with a velocity of 10,000 km/s!