AY-101-Dean Townsley-Exam 3

Luminosity

total energy output, electromagnetic radiation (Sun: 4x10^26 W). It is related to apparent brightness by distance.

Temperature

surface energy output per surface area, spectrum

Mass

Total material in star, primary parameter for stellar life

composition

amount of elements heavier than helium, how many "ancestors" stars had

Age

Is hard to measure, but critical to appearance of stars

True or false: Among two stars of the luminosity one that is dimmer is further away

true

Parallax

The angle that a star appears to move as the Earth moves around the sun

Parsec

1 parsec= 3.26 light-years

"Giant" Stars (high-mass giants)

Rigel: 17 solar masses, lifetime- 10 million years, age- around 5 million years, about 800 light years.

Betelgeuse: 23 solar masses, lifetime- 10 million years, age- 10 million years, distance- 400 light years

'Giant" Stars (low-mass giants)

Arcturus: 1.1 solar masses, lifetime: about 8 billion years, age 7.5 billion years, distance 37 light years

Sirius

(Brightest star) birth mass: 2 solar masses, lifetime: 1 billion years, age:1/4 billion years, distance: 8 light years

Transition to Giant

Stars become bigger when they run out of hydrogen in the center. Change from core hydrogen burning to shell hydrogen burning.

Open clusters

typically dissociated over time, mostly young.

Globular Clusters

More self-contained systems can be quite old (13 billion years)

Corona

Low-density, very hot gas around sun

Photosphere

"surface", source of light we see.

Convection Zone

Outer 1/3 beneath the photosphere. Vigorous "boiling due to heat movement.

Radiative zone

calm zone where high-intensity radiation moves heat outward

Core

inner 1/3, where energy is released by fusion; higher helium abundance

E=mc^2

E: energy

m= mass

c= speed of light

Magnetic field lines

Charged particles moving in a magnetic field feel force, which changes their paths. Crossing field lines creates as force that make particles spiral.

Solar Flares

Due to sudden rearrangements of magnetic field features, changes in magnetic field deposit lots of energy in the corona.

Stellar thermal equilibrium

Most objects: add energy= temperature increases

stars: add energy= temperature decreases

Density

same amount of stuff in a larger space= lower density

same amount of stuff in a smaller space= higher density

Star Formation

molecular clouds, gravitational collapse, mass distribution of stars, protostars, brown dwarfs

Stages of star formation

1. collapse of a fragment of a gas cloud

2. formation of a protostar (disk, jets)

3. Contraction and core heating

4. Ignition of fusion

what causes a gravitational collapse?

high density and low temperature

what is gravitational potential energy?

an energy source during contraction

Ignition of fusion

Birth, eventually contractions heat the core enough to initiate fusion reactions.

What is Substellar objects?

Failed stars, somewhere between giant planets and stars.

Evolution of low mass stars

-how they change as they age

-difference between low and high mass stars

-phases of burning

-Shell-burning giant stars

- White dwarf formation

Low mass stars

- sun

-vega

-sirius

-arcturus

-sirius B

high mass stars

Rigil

Betelgeuse

Main sequence structure

- central hydrogen fusion burning

- longest-lived stage

Planetary Nebula

The end of low-mass stars like the sun, heatedradiation from hot, newborn white dwarf stars by ultraviolet (temperature near 40,000k)

Horizontal Branch- Core helium burning

-Horizontal branch stars have similar luminosities due to similar core properties

-Different temperatures due to various amounts of mass loss while red giant.

Helium flash

Helium burning it ignited in core, reuses ashes of previous burning, re-establishes core burning, reduces overall luminosity (not shell burning)

Red Giant Phase

- Giants can fill a significant portion of the solar system

- Grows larger as shell burning source produces energy at a higher rate due to contraction

Hydrogen exhaustion, Giant formation

- As hydrogen runs out core and contracts and heats

- Using up of hydrogen in core forms inert helium core

- Hydrogen shell burning around helium core

- Shell burning very hot, high fusion rate

- High luminosity causes expansion (more surface area)

- Large convection zone

High mass

- Form neutrons stars or black holes after supernova

- shorter lifetime

- more than about 8 solar masses

Low mass

form white dwarf stars, no supernova

How do stars make elements with more protons and neutrons?

- Higher charged nuclei repel more

- Fusion of heavier, higher-charge nuclei requires higher temperatures

Remember for a star

losing energy= raising core temperature

Shell formation cycle

- use up core fuel

- form the inert core

- change to shell burning

- growth and contraction of core (raising temperatures)

-ignition of new fuel in the core

- repeat

Iron

Has the lowest mass (-energy) per nuclear particle

- No energy can be released by rearranging nucleons into some other nucleus

Core collapse supernova

Remove electrons= collapse

- Release of gravitational energy in collapse ejects most of stars

Wavelengths of light

Radio

Infrared

Visible Light

Ultra Violet

X-Rays

Gamma Rays

White dwarf stars

- cooling from being the hot core of a star

- higher mass star is smaller size

- held up by electron degeneracy pressure

-millions of times more dense than water teaspoon of white dwarf core = 100 tons

- low mass star

Degeneracy

particles that electrons are not allowed to occupy the same energy level

Pulsars

Neutron star, named after pulses we detected.

- Causes by radiation beamed from magnetic poles

- Born rapidly rotating as the core of stars collapses in a supernova.

Black holes

Speeds to hold up the neutron star

-Happens above about 3M sun, exact value uncertain.

Heaviest elements

Collision and destruction of a neutron star

- capture of neutrons (no charge= no repulsion!)

- This produces elements like Uranium and Plutonium.

Neutron capture

It occurs in a burning shell in giant stars to form uranium- like elements.