Lecture 28 Flashcards
How does the Hubble Tuning Fork hypothesise galaxy evolution?
Hubble proposed that galaxies evolved from early type elliptical galaxies to late type spiral galaxies
What is the approximate number of galaxies in the universe?
Approximately 70 billion
What does the galaxy stellar mass function show?
It shows that small galaxies are 100-1000x more common than massive galaxies
What do galaxies form from?
Giant gas clouds
What are the steps of galaxy formation?
- Gravitational stability
- Disk formation
- Hierarchical growth
4.
What is gravitational instability?
Gravity pulls mass together to form overdensities
What occurs during the disk formation step?
Angular momentum decides whether a galaxy will form a disk or spheroid shape
What occurs during hierarchical growth?
- multiple gas clouds collide to form larger galaxies from smaller ones
- old stars take random orbits in the halo
- as the galaxy grows older, new stars continue to form
- galactic cannibalism occurs: smaller galaxies and dust clouds are “eaten” by larger galaxies
What causes the arms within spiral galaxies?
The arms in spiral galaxies are spiral density waves. They are long lasting waves of molecular cloud and star collapse. They do not carry matter.
What causes the spiral structure within spiral galaxies?
Stars in galaxies move in elliptical orbits. The spiral arms are patterns within the galaxy, not physical structures. Stars move in and out of the arms.
What is the movement of gas and stars through the spiral arms?
- gas and dust clouds approach the arm
- gas clouds are compressed to form new stars
- young, blue stars eventually run out of energy and move out of the arm
- low mass stars are able to live long enough to move out of the arm
How can we observe the younger universe?
Since distance and time are intertwined, we can view very distant galaxies to view the early universe. This is as light travels at a finite speed.
(Imaging distant galaxies compresses information into 2D)
Why can the finite speed of light be used to view the distant past?
- photons transport information
- it takes time for the photons to reach us
- once the photons finally reach us they give us a snapshot of the past
When was the highest rate of galaxy formation in the universe?
The highest rate of galaxy formation occurred at around 3 billion years
What do galaxy collisions do to stars and gas?
They separate stars from gas and trigger new star formation from compressed gas clouds
