Our galaxy, the Milky Way is typical: it has hundreds of billions of stars, enough gas and dust to make billions more stars, and at least ten times as much dark matter as all the stars and gas put together. And it's all held together by gravity. There are approximately 170 billion galaxies in the observable universe. Most galaxies are 1,000 to 100,000 parses in diameter and usually separated by distances on the order of millions of parses ( or megaparsecs). The space between galaxies is filled with a tenuous gas with an average density less than one atom per cubic meter.