What defines a galaxy?

Answer 1

A century ago astronomers talked about only one galaxy, what they called the "Stellar System" or the Milky Way. The term "galaxy" was used almost synonymously with "universe," and when a distinction was drawn, the issue was mainly whether or not the universe had an extent beyond that of the stars. Twenty-five years later our galaxy was established as one of many and the study of what Edwin Hubble had first dubbed extragalactic nebulae was burgeoning. Astronomers had analyzed the light of other galaxies spectroscopically and determined that it was starlight. We still take this as one of the defining characteristics of a galaxy: its visible light comes primarily from stars. Today we are nearly overwhelmed with data on the immense diversity of galaxies, to the extent that it actually becomes difficult to write down a definition that distinguishes what is a galaxy from everything that is not.

Answer 2

Main Entry: gal·axy
Pronunciation: 'ga-l&k-sE
Function: noun
Inflected Form(s): plural -ax·ies
Etymology: Middle English galaxie, galaxias, from Late Latin galaxias, from Greek, from galakt-, gala milk; akin to Latin lac milk
1 a often capitalized : MILKY WAY GALAXY -- used with the b : any of the very large groups of stars and associated matter that are found throughout the universe
2 a : an assemblage of brilliant or notable persons or things b : WORLD 11

Answer 3

A short meaning dude:

--------> A bunch of stars together:

98% of a galaxy is vacuum

2% stars and other things
1.9% of that 2% are the SuperGiant Stars or Red Giants

the other 0.1% are the dwarf stars middle-size stars like our sun

In a galaxy scientists estimate that are 100 billion stars
and a HUGE BLACK HOLE IN ITS CENTER (including the Milky Way)

XOXO

Answer 4

I like this one:
a massive, gravitationally bound system consisting of stars, an interstellar medium of gas and dust, and dark matter.