Galaxies and the Universe Notes Galaxies and the Universe
The Milky Way Galaxy: a huge group of stars, gas, and dust held together by gravity. The Sun is part of the Milky Way galaxy.
The Milky Way Without a telescope, you only see nearby stars. Nearby stars are a tiny fraction of the several hundred billion in the galaxy.
The Milky Way The Milky Way is shaped like a disk with a bulge in the center. Because our view is from inside the galaxy, all we can see of the Milky Way is one arm of stars across the sky.
The Milky Way The Milky Way is more than 100,000 light years across. The Sun is about 28,000 light-years away from the center, which is a clump of densely packed stars.
The Milky Way In addition to stars, the Milky Way contains clouds of gas and dust called nebulae (plural for nebula). Heart nebula Orion nebula Carina nebula NGC 3603
The Milky Way The stars and nebulae orbit the center of the galaxy at high speeds. The Sun takes about 250 million years to orbit the Milky Way galaxy once.
Galaxies Galaxies range in size from a few hundred million stars to over a trillion stars. Galaxies also have different shapes.
Arms of stars, gas, and dust curve away from the center Disk-shaped with a central bulge Composed of both old and young stars Examples: Milky Way, Andromeda Spiral Galaxies
Andromeda Galaxy
Grand Design Galaxy
Southern Pinwheel Galaxy
Elliptical Galaxies Shaped like spheres or eggs. Very little dust and gas. Made entirely of old stars. Examples: IC 1101, M89
NGC 1132
M87
Irregular Galaxies Faint with no definite shape. Smaller than other types. Lots of gas and dust and many young stars. Examples: the large and small Magellanic Clouds
Large Magellanic Cloud
Small Magellanic Cloud
Centers of Galaxies Most large galaxies have supermassive black holes at the center. These black holes have masses millions or billions of times greater than the Sun.
Centers of Galaxies Supermassive black holes are so large that they often draw in huge whirlpools of gas from surrounding stars.
Centers of Galaxies If the center of a galaxy is bright, it may look like a star from very far away. Quasar: the bright center of a very distant galaxy. The galaxy surrounding a quasar is often hard to see because the quasar is so bright.
The Universe The Milky Way is one of at least 200 billion galaxies, though there are likely many more than that. Galaxies occur in groups called superclusters.
The Universe Between the superclusters are massive spaces of emptiness.
The Universe The elements found in our solar system and galaxy are found throughout the universe.
The Universe The same physical laws that govern our solar system and galaxy are also true throughout the universe.
Motion of Galaxies Have you ever noticed that the sound of a siren changes as it travels toward and then away from you? The pitch seems to get higher as it approaches, then drops as it moves away.
Motion of Galaxies This is the Doppler effect: a change in the observed frequency of a wave that occurs when the source of the wave or the observer is moving. https://www.youtube.com/wat ch?v=imoxDcn2Sgo
Motion of Galaxies The Doppler effect occurs with light as well as sound. Objects moving toward us have a “blue shift” because the light we are receiving is being compressed into shorter wavelengths.
Motion of Galaxies Objects moving away from us have a “red shift” because the light we are receiving is seemingly stretched into longer wavelengths.
Motion of Galaxies Most galaxies we observe from Earth have a red shift- meaning they are all moving away from us-and one another.
Motion of Galaxies This supports the idea that the universe is expanding.
Development of the Universe Because galaxies are moving apart, scientists concluded that there was a moment in time when the universe began to expand, which we call the big bang. This occurred around 13.7 billion years ago.
Development of the Universe After the big bang, the universe was extremely dense and hot. We still have a lot to learn about what the early universe was like. Stars began forming after about 1 billion years.