Lecture 27 Flashcards
What is a barred spiral galaxy?
A spiral galaxy with an elongated bulge
What are the key features of elliptical galaxies?
- few young stars
- very little cool gas/dust
- reddish colour due to old stars
- no disk, all bulge/halo
What are 3 theories for irregular galaxies?
- galaxies in formation
- galaxies in transition
- failed galaxies
What is a key feature of most irregular galaxies?
The have lots of star birth
What does Hubble’s Tuning Fork diagram try to relate?
It tries to relate galaxies to each other similar to how stars are related on an HR diagram
What are galaxies made of?
- mainly empty space
- cold gas and dust (10s of K)
- warm gas and dust (100-1000s of K)
- hot gas (10000K) near young stars
- superbubbles (10^5-10^7K)
- stellar black holes
- supermassive black holes
What are superbubbles?
- superbubbles are the combined effect of many massive stars’ wind and supernovae.
- they enrich the galactic gas with heavy elements
- they can blast hot gas out of the galaxy
What do the spectra at the centre of galaxies show?
They show gas rotating at high speeds; these rotational speeds can only be explained by a super-massive black hole
What is an active galactic nucleus?
- occurs when a SMBH is growing
- gas clouds fall into the core of a galaxy and produce an accretion disk (inner regions are hotter)
How is light emitted from an active galactic nucleus?
- it is emitted from the accretion disk outside the event horizon
- the more mass “eaten” the brighter
What are the main assumptions about quasars?
- very hot as they appear as extremely blue stars
- must be small due to rapid and dramatic variations in brightness
- extremely bright due to high redshifts (large distances)
What actually are quasars?
The most luminous active galactic nuclei
What do radio lobes show about quasars?
They show that there are huge amounts of energy present due to the lobes being many times larger than the galaxy
When were most quasars formed?
In the early universe less than 1 billion years after the big bang
What is the Small Magellanic Cloud?
A dwarf irregular galaxy with lots of star formation
