Cosmic origins final

Is the sun on fire?

No because fire is a chemical reaction and that would mean the sun would only last about 3,000 years

1853 JJ Waterston

Said that the sun was powered by meteoric infall

Meteoric infall

Converting kinetic energy to thermal energy

Problems with meteoric infall

1.) The sun would need a lot of meteors a day

2.) More meteors would hit the earth if that was the case

1862 Lord Kelvin and Herman von Helmoltz

Thought the sun was powered by gravitational contraction and meteoric infall and that the sun would be shrinking every day (would last 30mil years)

Sedimentation

Layered deposits can be used to determine age of the earth and geologist said that earth was 100mil years old

1911 Arthur Holmes

Calculated 370mil years old with radiometric dating

Radioactivity

Spontaneous emission of radiation (emits alpha particles and decays)

Marie, Piere, and Henry

Figured out the radiation that we use for half-life

Half-life

Time it takes for a radioactive sample to reduce its mass by half and emits radon in the process

Radio carbondating

Cosmic rays will be detected by water tanks when it hits nitrogen but Holmes used argon to calculate this number

Why was Arther Holmes so off?

We hadn’t discovered the neutron because he didn’t know there can be different isotopes, he did revise his number to 4.5 billion years

Makeup of an element

x=element symbol

z= atomic number (proton number) defines element

A= mass number (number of protons and neutrons)

What is the sun made up of?

74% hydrogen

24% helium

2% metals

What state of matter is the sun in?

Plasma (electrons jump up and separate because of heat)

What powers the sun?

Nuclear fusion

Nuclear fusion

Taking 2 small nuclei to make 1 large nuclei

Mass defect

Difference in the mass of the nucleons and the atom

Nuclear fission

Is a large atom that splits (ex: uranium 235)

E=mc²

E= energy

m= mass defect

c= speed of light

1916 Arthur Eddington

Observed variable stars (stars that get bigger/smaller) and disproves Kelvin/Helmholtz

1920 Eddington’s correct theory

Thinks the sun was powered by nuclear fusion

1939 Hans Bethe

Came up with the process called the proton-proton chain (and CNO cycle)

Proton-proton chain

Takes 4 protons to make helium

CNO Cycle

Not used as much, except for in stars that are greater than 1.3xs the mass of the sun (Ms)

Burning

Fusion

Nebula theory

Stars were thought to have been formed by a collapsing nebula (usually stellar, but ours was a solar nebula)

Nebulas

Are clouds in space that are mostly hydrogen and can form a star if they are triggered to collapse

What can cause a nebula to collapse?

Shockwave from supernova

Dwarf galexy passing by

Rogue passing star

Black hole passing by

Nebula collapse

Forms a protostar (collection of gas that cosplays a star)

Protostar vs Star

A star is an object large enough to sustain fusion

Structure of the sun

Core (fusion)

Radiative zone

Convection zone (photosphere=surface)-

Hydrostatic equilibrium

Stars are ballenced between thermal pressure (fusion) and gravity

Astronomical Units

The average distance from the earth to the sun

Lightyear

Distance light travels in one year

Paralax

Change in the position based on different view points

Stellar paralax

Apparent change in a star’s position against distant stars due to Earth’s movement around the sun

Distance and paralax

The farther the star, the less the paralax (limit = 100 parasecs = 326 light years)

Luminosity

Total power output of a star measure in watts (needs to account for dimness)

Brightness

Power per area in watts per square meter (is actually apparent brightness because light dims with distance)

Apparent magnitude

Same thing as apparent brightness in different units

Original magnitude scale

A scale created 129 BC by Hipparchus that goes from 1-6 (1=brightest) and was expanded to 25 with the telescope

Absolute Brightness/magnitude

How bright an object is at 10 parsec (doesn’t depend on distance)

Light

Electromagnetic wave on a spectrum (eye detects small visible spectrum)

Energy of light

Depends on frequency and is inversely proportional to the wave length (distance between trough/crest)

Max Planck

Discovered quantum mechanics

Atoms

Electrons have different energy level (orbitals)

Energy levels

Lowest= ground state

First excited state= n is 2

Second excited state= n is 3

How does an atom move up energy levels

Absorb light and then jumps back down to emit light (certain colors are different energy levels)

Spectral lines

See everything except what the atom absorbs (opposite for the emissions)

Henry Draper

Pioneer in astrophotography; has the oldest pic of the sun and took one of Vega too because he wanted to figure out why lines were missing (wife donated to Harvard)

Edwards Pickering

Director of Harvard Observatory who used the money to classify stars with the Harvard Computers

Harvard Computers

Women from Radcliffe College that were interested in astronomy

What was used to classify stars

Glass plates were used to classify stars

Antonia Maury

Pioneer in spectroscopic binary stars (published her own catologue)

Williamina Fleming

Pickering’s maid that was the first person in charge of classifying stars

Annie Jump Cannon

Was the fastest at classifying and came up with the spectral classes that we use today (OBFGKM)

Cecilia Payne

Used quantum mechanics to figure out the composition of the universe (rejected first) and figured out that Annie Jump Cannon ordered them by temperature (O=hotest)

1925

Cecilia Payne’s Disertation was on the composition of sun (mostly hydrogen and helium) and was the best one

Star’s color

Proportional to the surface temperature

What color is the sun?

Green (appears as white)

Blackbody

Idealized body that absorbs all radiation that falls on it and perfectly emits radiation

Wein’s Law

Alpha times the peak wavelength is equal to the constant b, over the temperature

Small wavelengths

The smaller the wavelength the hotter a star

Spectral Sequence

O→M were subdivided from 0-9 (hot to cool)

What spectral class is the sun?

G2V

Most common star

76% of stars are red dwarf stars (LTY on the spectrums)

Least common star

O stars are the least common because they burn through their fuel really fast (only last a few million years)

Brown Dwarfs

They can’t sustain fusion and are usually 13-18 MJ

What is lowest mass a star could be a brown dwarf

The lowest would is 80 MJ or 0.08 Ms

Stefan-Boltzmann Law

How we determine a star’s luminosity:

1.) Temperature (dominates)

2.) Radius

Hertsprung-Russle Diagram (H-R)

Main Sequence

A star that that is burning hydrogen in the core

Life of a star

Born→main sequence→death (runs out of hydrogen)

Mass

Tells you luminosity, lifespan, and temperature

Luminosity class

I.) Supergiant

II.) Bright giant

III.) Giant

IV.) Sub-giant

V.) Main sequence star (sun is a G2V)

Variable stars

Apparent magnitude of the star changes over time

Light Curve

Is a plot of the apparent magnitude over time

Extrensic Variable Stars

Exoplanet (exoplanet passes in front of the stars)

Eclipsing binary stars

Rotating variable stars (there are star spots)

Eruptive variable stars (large ejections of matter into space)

Intrensic Variable Stars

Star physically changes (pulsating variable star)

Instability Strip

Where most variable stars are

Henrietta Swan Leavitt

Investigated Variable Stars (cepheids)

Period

Time it takes a star to go from maxima to maxima (brightest back to brightest)

Period luminosity relationship

The brighter the star, the longer its period

Leavitts Law

Can use brightness of a cephid to measure the distance of stars

Limit of Leavitts Law

30million parsecs

Cepheids

Are important because they are bright and can be used to find the distance to other galaxies

Type 1 Cepheid

Are more luminous, massive, and have higher metallicity (is younger)

Type 2 Cepheid

Is the opposite of a type 1

Star’s mass at birth

Less than 2 Ms= low

2-8Ms= intermediate

8Ms+= high

Death process

1.) Inert helium core causes fusion to stop

2.) Initiates main sequence turn off (vertical)

3.) Outer layer eventually cools (moves right horizontally to the sub-giant branch)

4.) Hydrogen shell around the helim core causes burning and pushes outward (moves to red giant branch

Inert helium core

When hydrogen is exhausted

Main sequence turn off

Leaves the main sequence

Hydrogen shell

Surrounds the helium core and by proximity it ignites, causing an increase in luminosity and pushes outward to the red giant branch

What will happen to the sun when it is about to die?

It will eventually become 100x bigger and 1kxs more luminous (will only get up to luminosity class 3)

Dredge-up

During hydrogen shell burning CNO is brought to the surface and convection layer expands down to the hydrogen shell burning

Temperature to fuse helium

100 million kelvin

Tripple Alpha Process

3 Helium → 1 Carbon

Helium Flash

Runaway helium fusion event at the tip of the Red Giant Branch

Horizontal Branch

The distance it goes on this branch depends on how much mass is lost from burning (little mass lost= big dip) and has helium core burning (only one)