Presentation on theme: "Apparent Brightness α Luminosity/Distance^2"— Presentation transcript:
1 Apparent Brightness α Luminosity/Distance^2 What two things does the apparent (or perceived) brightness of an object depend on?How can this relationship be used to determine distances?Apparent Brightness α Luminosity/Distance^2
2 Creating the Heavy Elements How are the lives and deaths of stars related to the creation (and distribution) of the heavy elements?What is the heaviest element that can be created in the core of a star?
3 Stellar Deaths and the Creation of Heavier Elements A star will fuse heavier and heavier elements until:1) It can no longer achieve the core temperature needed to fuse heavier elements (low mass stars)or2) Iron is created in the core (highest mass stars)What is left behind when a low mass star dies?Red Supergiant
5 Stellar LifetimesIs the lifetime of a high mass star shorter or longer than that of a lower mass star?
6 Evolution of Stars > 8 MSun Eventual state of > 8 MSun starHigher mass stars evolve more rapidly (=> shorter lifetimes).Heaviest element made is iron.Products of outer layers become fuel for inner layers
7 NovaeWhat conditions are required for a nova to occur?
8 Stellar Explosions Novae Accreting white dwarf in a binary systemHow is this process related to a carbon-detonation supernova?What is the Chandrasekhar limit?
9 A Carbon-Detonation Supernova Despite novae, mass continues to build up on white dwarf (WD).If mass grows to 1.4 MSun (the "Chandrasekhar limit"), gravity overwhelms the Pauli exclusion pressure supporting the WD.This starts carbon fusion everywhere at once.Tremendous energy makes star explode. No core remnant.
10 Death of a Very High-Mass Star M > 8 MSunIron core at T ~ 1010 K radiation photodisintegrates iron nuclei into protons and neutrons.Absorbs enormous amount of energy => core collapses in < 1 sec.Result is a Core-collapse SupernovaWhat is left behind?
11 Testing our TheoriesWhy are star clusters useful for stellar evolution studies?1) All stars in a cluster formed at about same time (so all have the same age)2) All stars are at about the same distance3) All stars have same chemical compositionThe only variable property among stars in a cluster is mass!
12 Final States of a Star 1. White Dwarf If initial star mass < 8 MSun or so. (Low Mass)2. Neutron StarIf initial mass > 8 MSun and < 25 MSun . (Intermediate Mass)3. Black HoleIf initial mass > 25 MSun . (High Mass)
13 A neutron star over the Sandias? Neutron StarsConservation of Angular Momentum => Fast Rotation rate: few to many times per second.Huge Magnetic field: x Earth's!What type of object can these conditions produce?A neutron star over the Sandias?
15 Black Hole Geometry What is the “surface” of a black hole called? What physical property determines it's size?
16 Event horizon Schwarzschild Radius Event horizon: imaginary sphere around object with radius equal to Schwarzschild radius (determined by mass). “Surface” of black hole.Event horizonSchwarzschild Radius
17 According to Einstein's General Relativity, all masses curve space. How does this changeour understanding of thegravitational force?
18 Black HolesWhat are some of the strange phenomena we might encounter if we fell into a black hole?
19 Effects around Black Holes Near event horizon:1) Enormous tidal forces.2) Bending of light.2) Gravitational redshift.3) Time dilation.
20 The Equivalence Principle What two phenomenon did Einstein show produce effects that are indistinguishable from one another?
21 Einstein's Principle of Equivalence According to Einstein, the effects of gravity and acceleration are indistinguishable from one another!The laws of physics in a gravitational field and in a uniformly accelerating frame of reference are identical.