PX158 - J2 - types of galaxies

• there are three main types of galaxies

spiral galaxies

• contain a central region (bulge), and spiral 'arms'
• often contain young (blue) stars
• eg: milky way, $M31$

elliptical galaxies

• stars in an elliptical orbit around the centre
• extremely large
• contain old (red) stars
• potentially formed from the merger of spiral galaxies

irregular galaxies

• indistinct shape
• normally, small