A large number of variable stars in galaxies other than the Milky Way can usefully be observed by amateur astronomers. These are the objects on my observing program.
Historically, some star-like objects of varying brightness were catalogued as variable stars. BL Lac is a famous example; others include AP Lib and W Com. They were subsequently found not to be stars at all but the nuclei of galaxies. The optically varying component of the light from the nucleus comes from a relativistic jet of particles being expelled from the vicinity of a supermassive black hole. BL Lac is now catalogued as a blazar, as is Markarian 421 which appears below. Quasars form another species in the AGN (active galactic nuclei) zoo, of which 3C 271 is the brightest and best known.
|AE And||SDOR||15.1 – 17.6||In M31|
|AF And||SDOR||15.4 – 17.6||In M31|
|M31N 2008-12a||NR||18.0 – <23||In M31|
Active galactic nuclei
|Mrk 421||BLLAC||12.0 – 13.9||Markarian 421|