The Galactic Empire

[Argonavis (William)]

For those who like to collect lists and numbers, it appears that in addition to the known 13 satellite galaxies of the Milky Way:

http://www.astro.uu.se/~ns/mwsat.html

a further 2 have been detected in

Bootes

http://cul.arxiv.org/abs/astro-ph/0604355

and Canes Venatici

http://cul.arxiv.org/abs/astro-ph/0604354

[Greg Bryant]

I saw that in my inbox. Sloan has also uncovered a previously unknown stream of stars (as announced this week). We still don't have a full grasp of our galactic neighbourhood.

[vespine]

Newb alert:

Why is Andromeda not on that list? I thought that was a really close one too? It's a different category or something?

EDIT: ok, found it here http://anzwers.org/free/universe/localgr.html if you zoom out...

So what's the difference between LMC and Andromeda? I should probably just google it I'm guessing size? Is there something else?

[Volans]

G'day Vespine,

The LMC is known as a "dwarf irregular satellite galaxy". That just means it's small and lumpy in shape but the important bit is "satellite". The Milky Way being a rather large galaxy therefore has a fair amount of gravity. The LMC is gravitationaly bound to the Milky Way and is very very slowly colliding with us. The reason the LMC and the SMC are irregular in shape is because the Milky Way's gravity is distorting them.

The Andromeda Galaxy is a very large galaxy (bigger than us) and also a fair distance off compared to the LMC and SMC. The LMC/SMC are around 200,000 light years away whereas the Andromeda Galaxy is about 2.25 million light years away. So at that distance there is no way it could be a satellite galaxy to ours.

Peter.