Galactic surveys: Small galaxies are growing smaller
Abstract
Galaxies are not always giant collections of billions of stars. Since the 1930s, when Harlow Shapley discovered the first dwarf spheroidal galaxies, technology has allowed the detection of ever fainter galaxies in our immediate neighbourhood. Our galaxy is now known to have a whole retinue of very small satellite galaxies, the lowest luminosity examples of which can hardly outshine one massive star. Some galaxies appear to be getting physically smaller. Evidence for this is found in the streams of stars detected around our galaxy and elsewhere and in galaxies that appear to have had their outer regions truncated. Recent surveys of galaxy clusters have revealed another new class of object, the ultra-compact dwarfs. Though no less luminous than other dwarf galaxies, their physical sizes, of order 20 pc, are far below anything previously seen. They are reminiscent of the nuclei of dE,N type galaxies and may well be descended from them via some destructive processes within galaxy clusters.
- Publication:
-
Astronomy and Geophysics
- Pub Date:
- December 2004
- DOI:
- 10.1046/j.1468-4004.2003.45606.x
- Bibcode:
- 2004A&G....45f...6P