Our Galaxy, the Milky Way Galaxy

Milky Way Galaxy is a disc galaxy (aka spiral)

It has a bulge and a disc. Most of the stars in the galaxy are in the disc. Sun is 25-30 thousand light years away (about halfway) from the center. Disc has spiral arms, like a pinwheel. Stars in the center of the galaxy are moving faster than the star near the ends of the arms. Spiral arms are continually created and destroyed as the galaxy rotates. Takes a few 100 million years to rotate. Is about 5 billion years old. Our solar system rotated 20-25 times around the center of the galaxy since it's creation.

Our solar system orbits the galaxy

It takes 200-250 million years to orbit the galaxy

MACHOS

Massive Astrophysical Compact Halo Objects -Dark matter is made up of very faint normal matter (like brown dwarfs or M Main Sequence Stars) -Probably not a correct theory because the amount of Brown Dwarfs would emit some infrared and we cannot detect anything

Diffuse Nebula

More DENSE area of ISM surrounded by a less dense area of ISM Called diffuse nebula because it is diffuse by human standards Stars are born in here (in the spiral arms of the disc in the Milky Way Galaxy) Nebula are many light years across 100s of stars can be born in the solar nebula 3 categories (Categorized on how it deals with visible light (aka photons)): Absorption Nebula, Emission Nebula, and Reflection Nebula The further away a star is, the greater the errors can be when calculating their temperature/color because of the ISM interference The further away a star is, the more reddening occurs

binary star systems

Most star systems in the Milky Way Galaxy are binary star systems

Globular (Cluster of population II stars - All stars outside the Milky Way Galaxy)

Old (via Main Sequence Turnoff is late) As old as 10 billion years Some are the oldest things in the Universe Dust poor Gas poor Aspherically shaped Hundreds of thousands of stars to million of stars Spherically shaped, gigantic circular orbits Low Metallicity visible light cannot get through, but photons can Outside of the plain of the Milky Way Galaxy Has no O, B, A, F, and G stars in here Formed first

Outer Space

Outer space is not a perfect vacuum, that is a common misconception that it is.

Emission Nebula

Prefers long wavelengths Emits red light Sunrise and sunset skies are red because of this Reddening (blue light has been removed, red light has not been added)

Reflection Nebula

Prefers short wavelengths Reflects/scatters all light Emits blue light Daytime sky is blue because of this

Bubble

Region around O and B stars that have less ISM (and therefore density) around them because the stars are pushing the ISM away via radiation pressure

Shape of the Milky Way Galaxy

Shaped somewhat like a pin wheel with spiral arms, and our solar system is in one of these spiral arms roughly half way from the center of the Milky Way Galaxy. roughly 25,000 light years away.

Super Massive Black Hole Origins

We do not know where the Super Massive Black Hole came from, which is a couple of million solar masses. One theory is that it eats things around it and grows larger and larger. The Details are not yet understood.

WIMPS

Weakly Interacting Massive Particles -Dark matter is made up of Susy particles -All theory. No one has detected Susy particles -A selectron, glueinos, weenoes, zeenoes, squark, gravatinoes and other particle that has not been proven yet

MOND (Modified Newtonian Dynamics)

Some people say that there is no Dark Matter, but there is just another theory of gravity (Newtonian gravity is too weak)

Star cluster

Star cluster - Collection of hundreds (maybe thousands) of stars

Rotation Curve

Stars near the edges of galaxies move at the same speed as the stars near the center. -Flat, the laws of gravity and physics can be used to figure out why -Creating a massive halo that emits no light

Galactic Dynamics

Study of the shape of galaxies and how they change (by studying the orbits of the individual stars)

Observational Galactic Dynamicists

Take photographs of galaxies and study their shapes and also study how the stars rotate in a galaxy

Dark Matter Halo

The Milky Way Galaxy is surrounded by a Dark Matter Halo, and this is what holds the galaxy together. We have no clue what it's made up of because it doesn't radiate any sort of light (visible or otherwise)

Thickness of the Milky Way Galaxy

1,000 light years thick

Dark Matter

90% of all galaxies and the Universe are made up of Dark Matter

Absorption Nebula

Absorbs all light Looks black

Redding

All galaxies are moving away from us and look red because of this

Super Bubbles

Around O/B associations About as thick as the Milky Way Galaxy itself! Super bubbles will grow (and move more ISM) when the O and B stars go supernova Remember, the gas is still moving around randomly!

We don't know why galaxies have arms

The computer simulations tell us this

ISM

InterStellar Medium Radiation pressure is pushing ISM away from O and B stars The ISM is frothy (some parts are thicker/denser than others via randomness) We cannot see past a few thousand light years in the PLANE of the Milky Way Galaxy because of ISM

The rotation of the Milky Way Galaxy

Is slow, the galaxy has rotated about 40-50 times since it's creation

Size of Milky Way Galaxy in light years

100,000 light years across

Black holes do not hold galaxies together

Black holes are light compared to the rest of the galaxy (1%)

O/B associations

Clusters of O and B stars

Galaxy

Collection of stars, dust and planets and anything else

Machos or Wimps

Dark Matter could be made up of Machos or Wimps

Gas

Gas permeates the entire Milky Way Galaxy (and any other galaxy). 75% atomic hydrogen (just hydrogen atoms) and 25% helium Gas does not even feel gravity (because it is so diffuse) Gas is moving around randomly because of this

21cm Photons

Hydrogen - Proton with an electron "orbiting" it and spinning on its own axis Second most common photon in the Universe Photons spit out when the spins start out aligned and go anti-aligned Easily able to traverse the plain of the Milky Way Galaxy which is how we figured out the shape of the Milky Way Galaxy The wavelength of the photon is 21cm Not a visible light photon (microwave or infrared) constructed a map

Super Massive Black Hole

There is a super massive black hole at the center of our (and every other) galaxy that is maybe a billion solar masses

Theoretical Galactic Dynamicists

Write computer simulations to show how a galaxy changes. Most powerful computers can only do simulations with millions of stars.

Open (Cluster of population I stars - All stars inside the Milky Way Galaxy)

Young (via Main Sequence Turnoff is early) Dust rich Gas Rich Hundreds to a thousand of stars Irregularly shaped In the plain of the Milky Way Galaxy Sun is in here High Metallicity

Milky Way Galaxy

made up of roughly 100 billion star systems that are shaped like a flat disk