Our Galaxy Lecture Notes

Flashcards about the Milky Way Galaxy.

Milky Way Features

The primary features of our galaxy are the disk, bulge, halo, and globular clusters.

Distance to Galactic Bulge

There are 27,000 light-years between the Sun and the galaxy’s bulge.

100,000 light-years

The approximate span of the Milky Way galaxy.

Orbit of Disk Stars

Stars in the disk all orbit in the same direction with a little up-and-down motion.

Orbit of Halo and Bulge Stars

Orbits of stars in the bulge and halo have random orientations above and below the disk.

Reason for Bulge Star Motion

Gravity of disk stars pulls them toward the disk.

Likelihood of Stellar Collisions

It is unlikely due to the vast distances between stars compared to their sizes.

v in Orbital Velocity Law

Orbital speed

r in Orbital Velocity Law

Radius

M in Orbital Velocity Law

Mass within an orbit

What determines mass within an orbit?

The orbital speed and radius of an object on a circular orbit around the galaxy.

Structure of our Galaxy

Our galaxy consists of a disk of stars and gas, with a bulge of stars at the center of the disk, surrounded by a large spherical halo.

Star-Gas-Star Cycle

Gas from old stars is recycled into new star systems.

Molecular Cloud Formation

Gas in the disk gradually cools and forms molecules.

Element Creation in Stars

Fusion in the cores of stars makes new elements from hydrogen.

Gas Return to Interstellar Space

Supernovae and stellar winds return gas and new elements to interstellar space.

Formation of Atomic Hydrogen Clouds

Returning gas cools and then blends into atomic hydrogen clouds.

Stellar Winds from High-Mass Stars

High-mass stars have strong stellar winds that blow bubbles of hot gas in the interstellar medium.

Gas Return from Low-Mass Stars

Lower-mass stars return gas to interstellar space through stellar winds and planetary nebulae.

X-rays from Supernova Remnants

X-rays from hot gas in supernova remnants reveal newly made heavy elements.

Element Mixing in Interstellar Medium

New elements made by a supernova mix into the interstellar medium.

Radio Emission from Supernova Remnants

Radio emission in supernova remnants is from particles accelerated to near light speed.

Superbubbles

Multiple supernovae explosions in a young star cluster create huge hot bubbles.

Gas Cooling in the Halo

Hot gas in the halo cools & forms clouds that can rain back down on the disk.

Atomic Hydrogen Formation

Atomic hydrogen gas forms as hot gas cools, allowing electrons to join with protons.

Molecular Cloud Formation Process

Molecular clouds form after gas cools enough to allow atoms to combine into molecules.

Star Formation in Molecular Clouds

Gravity forms stars out of the gas in molecular clouds.

Element Creation by Stars

Stars make new elements by fusion.

Expulsion by Dying Stars

Dying stars expel gas and new elements, producing hot bubbles.

Hot Gas Cooling

Hot gas cools, allowing atomic hydrogen clouds to form.

Molecular Cloud Formation

Further cooling permits molecules to form, making molecular clouds.

Star and Planet Formation

Gravity forms new stars (and planets) in molecular clouds.

Where will the galaxy’s gas be in 1 trillion years?

Locked into white dwarfs and low-mass stars.

Dust Cloud Effect

Dusty clouds in the disk block much of our galaxy’s visible starlight.

21-cm Radio Waves

Radio waves emitted by atomic hydrogen show where gas has cooled and settled into the disk.

CO Radio Waves

Radio waves from carbon monoxide (CO) show locations of molecular clouds.

Infrared Emission

Long-wavelength infrared emission shows where young stars are heating dust grains.

Infrared Light Use

Infrared light reveals stars whose visible light is blocked by gas clouds.

X-rays from Hot Gas

X-rays are observed from hot gas above and below the Milky Way’s disk.

Gamma Rays

Gamma rays show where cosmic rays from supernovae collide with atomic nuclei in gas clouds.

Ionization Nebulae

Ionization nebulae are found around short-lived, high-mass stars, signifying star formation!

Reflection Nebulae

Reflection nebulae scatter the light from stars.

Squeezing of Gas Clouds

Gas clouds get squeezed as they move into spiral arms.

Halo Star Formation

Halo stars formed first, then stopped.

Star Streams

Streams of stars show smaller galaxies being incorporated into the Milky Way galaxy.

Average separations of galaxies in the past compared to today

They were smaller.

Galaxy Formation

Our galaxy is formed from a cloud of intergalactic gas.

Mass at Galactic Center

Orbits of stars indicate a mass of about 4 million MSun.

X-Ray Flares

An x-ray flares from a galactic center suggest that tidal forces of the black hole occasionally tear apart chunks of matter about to fall in, rather than a smooth infall of material.

What orbits the center of our galaxy

Stars appear to be orbiting something massive but invisible… a black hole?