Agenda Types of star deaths Relativity Black holes Evidence for both Start registering your clickers. There’s a link from webct.

He core contracting H fusing Exterior expanding H runs out: star becomes a red giant

Mass alone determines death Small mass: White dwarf Med. Mass: Neutron star or pulsar Large mass: Black hole Determined by S. Chandreskhar

What type of death will our Sun die? What will happen to us?

Sun’s fate Diameter (times present value) Age (billions of years) Contraction First Red giant peak Now Leaves Main sequence White dwarf Orbits of: Mars Earth Venus Mercury Helium shell flashes

Sun’s fate Diameter (times present value) Age (billions of years) Contraction First Red giant peak Now Leaves Main sequence White dwarf Orbits of: Mars Earth Venus Mercury Helium shell flashes

Sun’s fate Diameter (times present value) Age (billions of years) Contraction First Red giant peak Now Leaves Main sequence White dwarf Orbits of: Mars Earth Venus Mercury Helium shell flashes

Death of a low mass star Red giant shrinks, becomes very hot Expands to become a red giant again Outer layers ejected into space.

Death of a low mass star Planetary nebulae are formed Eventually becomes a white dwarf

On the HR diagrams, white dwarf stars are A. On the upper right B. On the upper left C. On the lower right D. On the lower left

The Hertzsprung-Russell (HR) Diagram O B A F G K M Spectral Class Sun Main Sequence Stars White Dwarf Stars Red Giant Stars Hot, not too bright Absolute magnitude

Higher mass stars Fusion of heavier elements Contraction (increasing temperature) Cycle continues until core is made of Fe (iron)

Death of higher mass stars Explodes in a type II supernova Then becomes  a neutron star  or a black hole

Supernova 1987A (Type II) Gas from the explosion hitting cool ring of gas NASA

Neutron stars Fe core collapses Electrons enter nuclei, neutrons and neutrinos formed Carries energy outward, causing an explosion

Neutron star or black hole? If very massive it becomes a black hole Otherwise it the remaining core is called a neutron star  If this spins, we call it a pulsar Jocelyn Bell Burnell discovered pulsars!

What’s a theory? Start with an hypothesis  Must fit evidence  Testable  Falsifiable

Einstein’s theory of Relativity Fits evidence? Testable? Falsifiable?

Matter tells space-time how to curve Relativity in a nutshell Space-time tells matter how to move

Evidence – time dilation Viking Lander sent a signal to Earth Space was stretched, so time was too! Earth Viking Lander Sun

Evidence – GPS Many of us own GPS receivers. Uses time signals from satellites orbiting Earth. Does not work unless corrected for relativity! wikipedia; DoD

Evidence: Wobble of Mercury Cornell Shown by Einstein

Evidence: gravitational lensing Demo: bending light

Evidence: gravitational lensing

Demo: Lensing in water

When a star stops fusing If it has more than 25 X M sun  No outward force can resist gravity It will become a black hole Nothing on the surface can escape (including light)

What forces act between a black hole and a nearby object? Gravity is the only force acting!!!! Depends on:  Mass of objects  Distance between them If the sun turned into a black hole, what would happen to the Earth?

Can you get sucked into a black hole?

Escape velocity How fast does the shuttle have to go in order to leave Earth’s surface? 7 miles every second! (25,000 mph) The moon? 5320 mph The Sun? 1.38 million mph

Escape velocity Depends on the gravity between you and the object you want to escape! For a black hole, the escape velocity (inside the event horizon) is greater than the speed of light!

Do Black Holes Really Suck? event horizon Normal Weird Singularity The center of a black hole is a sphere (so is the event horizon)

Field trip to a black hole!! event horizon Normal Weird Singularity Volunteers?

At the event horizon Time slows waaaaayyy down Someone jumping in would die a nasty death Someone watching would see the person freeze in time

Finding black holes How can we see something that emits no light? Look for binary systems Make sure candidate is not a neutron star!

Finding black holes Matter near the black hole is traveling close to the speed of light When it rubs together, it gives off x rays we can see NASA/CXC

Summary Relativity tells us space and time can be stretched Escape velocity, event horizon Black holes can be found, but not directly seen