High Mass Stars and then Stellar Graveyard 7/16/09 Astronomy 101
Astronomy Picture of the Day Astronomy 101
Something Cool Betelgeuse Astronomy 101
Outline for Today Astronomy Picture of the Day Something Cool Business Return Lab 6 Q&A session High Mass Star Evolution White Dwarfs, Neutron Stars, & Black Holes Minute Writing Break Lab 8 Astronomy 101
Questions for Today What happens to massive stars when they run out of Hydrogen? What happens when a star goes supernova? What supports white dwarfs and neutron stars? How do neutron stars pulse? What makes something a back hole? Astronomy 101
The evolutionary track of a 1M, star Fades Cools
Hydrogen Fusion Core Collapse, Hydrogen Shell Burning Onion Layer Shell Burning Helium Core Burning, Hydrogen Shell Burning Hydrogen and Helium Shell Burning, Carbon Core Outer layers Ejected Planetary Nebula White Dwarf Iron Core Supernova (type II) Neutron Star Black Holes
Hydrogen Fusion Core Collapse, Hydrogen Shell Burning Onion Layer Shell Burning Helium Core Burning, Hydrogen Shell Burning Hydrogen and Helium Shell Burning, Carbon Core Outer layers Ejected Planetary Nebula White Dwarf Iron Core Supernova (type II) Neutron Star Black Holes
When Hydrogen Runs Out... Core contracts and heats Helium fusion immediately sparked Hydrogen fusion continues in shell Star gets bigger H H He
When Helium Runs Out... Core contracts and heats Carbon fusion immediately sparked Helium and Hydrogen fusion continues in shell Star gets bigger H H He H HeC
Onion Layer Burning
Like all desperate measures, each fix is less successful than the first Core is hotter and hotter each time. Burn rate is faster and faster but less and less energy is released per fusion reaction (i.e. energy difference between H and He is particularly large). Each Cycle is shorter than the one before!
Like all desperate measures, each fix is less successful than the first Core is hotter and hotter each time. Burn rate is faster and faster but less and less energy is released per fusion reaction (i.e. energy difference between H and He is particularly large). Each Cycle is shorter than the one before!
For a massive star H-burning: 7 million years (107 K) He-burning: 500,000 years (109 K) C-burning: 600 years (1011 K) Ne-burning: 1 year (1012 K) O-burning: 6 months (1013 K) Si-burning: 1 day! (1014 K)
What would happen if carbon had the smallest mass per nuclear particle? A) Supernovae would be more common B) Supernovae would never occur C) High-mass stars would have hotter cores D) Iron would be more abundant
What would happen if carbon had the smallest mass per nuclear particle? A) Supernovae would be more common B) Supernovae would never occur C) High-mass stars would have hotter cores D) Iron would be more abundant
Hydrogen Fusion Core Collapse, Hydrogen Shell Burning Onion Layer Shell Burning Helium Core Burning, Hydrogen Shell Burning Hydrogen and Helium Shell Burning, Carbon Core Outer layers Ejected Planetary Nebula White Dwarf Iron Core Supernova (type II) Neutron Star Black Holes
Hydrogen Fusion Core Collapse, Hydrogen Shell Burning Onion Layer Shell Burning Helium Core Burning, Hydrogen Shell Burning Hydrogen and Helium Shell Burning, Carbon Core Outer layers Ejected Planetary Nebula White Dwarf Iron Core Supernova (type II) Neutron Star Black Holes
Iron has the least mass per nuclear particle. END OF THE LINE!
Hydrogen Fusion Core Collapse, Hydrogen Shell Burning Onion Layer Shell Burning Helium Core Burning, Hydrogen Shell Burning Hydrogen and Helium Shell Burning, Carbon Core Outer layers Ejected Planetary Nebula White Dwarf Iron Core Supernova (type II) Neutron Star Black Holes
Hydrogen Fusion Core Collapse, Hydrogen Shell Burning Onion Layer Shell Burning Helium Core Burning, Hydrogen Shell Burning Hydrogen and Helium Shell Burning, Carbon Core Outer layers Ejected Planetary Nebula White Dwarf Iron Core Supernova (type II) Neutron Star Black Holes
The Death Throes of a High Mass Star It really really really runs out of fuel. Low mass stars run out because they don t get hot enough to burn what they have left. High mass stars run out because they ve burned everything! everything Can t burn iron!
When fusion stops: Core cools. Pressure drops Star collapses! This releases a huge amount of the star s gravitational potential energy! Used to be Massive & Big! Now it s Massive & Tiny!
Uh oh Over a solar mass of fuel burns in less than a DAY! HUGE LUMINOSITY!
Supernovae in other galaxies can be as bright as the whole galaxy! Can see them at HUGE distances!
More Fusion During Explosion We re made of all the elements created while powering desperate stars or during supernova explosions
Hydrogen Fusion Core Collapse, Hydrogen Shell Burning Onion Layer Shell Burning Helium Core Burning, Hydrogen Shell Burning Hydrogen and Helium Shell Burning, Carbon Core Outer layers Ejected Planetary Nebula White Dwarf Iron Core Supernova (type II) Neutron Star Black Holes
Hydrogen Fusion? Core Collapse, Hydrogen Shell Burning Onion Layer Shell Burning Helium Core Burning, Hydrogen Shell Burning Hydrogen and Helium Shell Burning, Carbon Core Outer layers Ejected Planetary Nebula White Dwarf Iron Core Supernova (type II) Neutron Star Black Holes
Hydrogen Fusion? Core Collapse, Hydrogen Shell Burning Onion Layer Shell Burning Helium Core Burning, Hydrogen Shell Burning Hydrogen and Helium Shell Burning, Carbon Core Outer layers Ejected Planetary Nebula White Dwarf Iron Core Supernova (type II) Neutron Star Black Holes
Neutron Stars and Black Holes Like White Dwarfs, Dwarfs dense, non-fusion remnants of stars
Hydrogen Fusion Core Collapse, Hydrogen Shell Burning Onion Layer Shell Burning Helium Core Burning, Hydrogen Shell Burning Hydrogen and Helium Shell Burning, Carbon Core Outer layers Ejected Planetary Nebula White Dwarf Iron Core Supernova (type II) Neutron Star Black Holes
Hydrogen Fusion Core Collapse, Hydrogen Shell Burning Onion Layer Shell Burning Helium Core Burning, Hydrogen Shell Burning Hydrogen and Helium Shell Burning, Carbon Core Outer layers Ejected Planetary Nebula White Dwarf Iron Core Supernova (type II) Neutron Star Black Holes
White Dwarfs Remnants of Low-Mass Stars (less than twice the mass of the Sun)
White Dwarfs are bizarre. They re really dense. Most of the mass of the star is now in a sphere the size of the Earth! ~2000 kg/cm3 or ~ton per teaspoon
How did they get so dense? 1.Fusion stopped 2.Temperature dropped 3.Pressure dropped 4.Gravity won! 5.Collapse! But what stopped the collapse? Normal gas pressure has failed, so it has to be something else.
Electron Degeneracy Pressure Gravity is trying to squish electrons into a small space. Quantum Mechanics says no two electrons can be in the same state (position and speed). Squishing electrons into a small space forces them to have the same position, so they must increase their speeds to have different states! This creates pressure! Note that this pressure does NOT depend on temperature!
White dwarfs collapse until they are dense enough that quantum mechanical pressure takes over! Nuclei Stationary Electrons Moving! Speeds set by quantum mechanics, not temperature! Only source of pressure!
Differences between thermal and degeneracy pressure Pressure Density Temperature Normal Gas: Pressure Density Temperature Degenerate Electron Gas: These cause white dwarfs to behave very differently than normal stars!
Size of a White Dwarf White dwarfs with same mass as Sun are about same size as Earth Higher mass white dwarfs are smaller White Dwarfs are Not Like Chocolate Cake
Which of these objects has the smallest radius? A) a 1.2 solar mass white dwarf B) a 0.6 solar mass white dwarf C) Jupiter D)a 1.2 solar mass main sequence star
Which of these objects has the smallest radius? A) a 1.2 solar mass white dwarf B) a 0.6 solar mass white dwarf C) Jupiter D)a 1.2 solar mass main sequence star
What happens as white dwarfs get more massive? More mass -> higher gravity Higher gravity -> more squished electrons Electrons move faster to get into different states. Electrons cannot move faster than light! White dwarfs have an upper mass limit: Chandrasekhar Mass ~ 1.4 M solar masses
How could white dwarf masses sometimes become higher than the 1.4M, Chandrasekhar mass??
What Happens if the Mass is Greater than 1.4 Solar Masses? Neutron Star, product of the death of a high mass star
What happens to the core or a high mass star when fusion stops: Core cools. Pressure drops Star collapses! It tries to support itself with electron degeneracy pressure But, M > 1.4Mp!!!! Collapses more! It s hot and dense But it can t detonate, since iron can t burn
Electrons just can t handle it! Electron degeneracy pressure fails. Lattice of nuclei breaks. Star compresses. Electrons and protons MERGE to form neutrons! Also forms neutrinos as a by-product.
The whole core becomes solid NEUTRONS!!! Dense as the nucleus of an atom! Held together by gravity NEUTRON STAR
Dying massive stars form neutron stars Neutron Star Tiny! 10-5 times smaller! Rotates several times a second! Core now held up by Neutron Degeneracy Pressure!
Observing Neutron Stars Found them by accident!!!! Jocelyn Bell noticed repeating pulses in her radio telescope Pulsar (Well, first called LGM)
Observing Neutron Stars
Pulsar at center of Crab Nebula pulses 30 times per second
X rays Visible light
Rotation was the only reasonable mechanism for producing these pulses Lighthouse model Only a neutron star could rotate that fast and not get ripped apart!
Pulsars
Which of the following is correct? A) All neutron stars are pulsars B) Pulsars can have different rotation speeds than pulsation times C) Some pulsars are not neutron stars D) Aliens on a different planet would identify different neutron stars as pulsars than we do
Which of the following is correct? A) All neutron stars are pulsars B) Pulsars can have different rotation speeds than pulsation times C) Some pulsars are not neutron stars D) Aliens on a different planet would identify different neutron stars as pulsars than we do
What happens if neutron degeneracy pressure can t support the core either? Collapses some more! (M > 3M or so?) Nothing (we know of) can stop it! BLACK HOLE! A black hole is black because light cannot escape from it
All objects have an Escape Velocity Escape Velocity = how fast something on the surface of an object has to go to escape the object s gravitational grip Depends on mass & size V = 2GM/R 2
Escape velocity depends on mass and size! Moon: 2 km/s Earth: 11 km/s Sun: 620 km/s White Dwarf: 7,600 km/s Neutron Star: 160,000 km/s When the escape velocity is larger than the speed of light, NOTHING CAN GET OUT! c 300,000 km/s V = 2GM/R 2
So how smooshed do you have to get to be a black hole? V = 2GM/R = c 2 2 2GM Rs = 2 c Rs = Schwarzschild Radius If an object s mass is compressed within Rs, the escape velocity is greater than the speed of light, nothing can get out, and it s a BLACK HOLE!
What s Your Schwarzschil d Radius? 2GM Rs = 2 c M ~ 70 kg G ~ 6.7 10-11 m3 kg-1 s-2 C ~ 3 108 m s-1
What s Your Schwarzschil d Radius? 2GM Rs = 2 c M ~ 70 kg Rs ~ 10-25 m! Smaller than a nucleus!
What about the Sun? 2GM Rs = 2 c M ~ 2x1030 kg G ~ 6.7 10-11 m3 kg-1 s-2 C ~ 3 108 m s-1
What about the Sun? 2GM Rs = 2 c M ~ 2x1030 kg Rs ~ 3 km! Still tiny! Smaller than a neutron star!
What does the Schwarzschild radius mean? If you re inside Rs, you can never leave! EVENT HORIZON Since not even light can get past the event horizon, there is no way of knowing what goes on inside.
What does the Schwarzschild radius mean? If you re well outside Rs, the black hole acts like any other mass.
What Would Happen to the Earth if the Sun were to Turn into a Black Hole? A) The Earth would spiral into the Sun B) The Earth would be sucked directly into the Sun C) The Earth would move away on a tangent to the orbit D) The Earth would continue in the same orbit
What Would Happen to the Earth if the Sun were to Turn into a Black Hole? A) The Earth would spiral into the Sun B) The Earth would be sucked directly into the Sun C) The Earth would move away on a tangent to the orbit D) The Earth would continue in the same orbit
A black hole s mass strongly warps space and time in vicinity of event horizon Event horizon
What Would Happen If You Fell Into a Black Hole?
Stars orbiting a black hole in X-ray source the center of the galaxy? Stars move so fast that there has to be a huge mass in a very small space! BH????
Something Cool Super-Massive Black Holes Astronomy 101
Summary of Star Death core Low-mass star rest High-mass star core rest Highest-mass star core rest white dwarf planetary nebula neutron star supernova remnant black hole supernova remnant
Type 1a Supernovas (White Dwarf Supernovas) From binary systems with one white dwarf
What are binary stars? The stars in the binary are born: At the same time From the same molecular cloud However, the stars in the binary can have: Different masses Different lifetimes
Binaries can change with time: 2 main sequence stars Higher mass star has evolved into a white dwarf If the two stars are close enough, matter can jump from the red giant onto the white dwarf! Lower mass star expands into a red giant
Before mass transfer Lattice of Helium & Carbon nuclei Electrons moving at the speed of light 1.4Mp white dwarf After mass transfer Electrons can t supply any more pressure Lattice breaks! Star collapses! >1.4M star formerly known as white dwarf
After mass transfer Electrons can t supply any more pressure Lattice breaks! Star collapses! Stuff falling in = hotter + denser Helium and/or Carbon nuclei can now fuse! fuse Star gets even hotter >1.4M star formally known as white dwarf
The star ignites! Helium and/or Carbon nuclei can now fuse! Star gets even hotter But, the star is still degenerate degenerate Pressure Density Temperature
If it weren t degenerate: Normal Star: If the Pressure Density Temperature temperature goes up: Pressure increases Star swells Star cools back down The rate of fusion drops back down The rate of fusion self-regulates
Degenerate Star: Normal Star: If the Pressure Density Temperature temperature goes up: Pressure doesn t change! The rate of fusion goes up! The temperature goes up more! The rate of fusion goes up more! Detonation
Minute Writing What ideas need reviewing before the test? Astronomy 101
Assignments No New Reading! No New Lab! No News Article Due! Look over the study handout and come with questions on it on Tuesday Astronomy 101