our sun and 10% the size of our sun. That still leaves between 40–80 billion stars much like the sun. If one in five of those has an Earth-like planet, that means there may be between eight and sixteen billion Earth-like planets in the Milky Way. Of course these numbers may be off. The number of sun-like stars may be lower, or higher. The number of Earth-like planets may be more, or less. We just can’t know, so far. Further, there is no reason to assume that only stars like our sun will have planets capable of supporting life. Or that only a planet will support life. There may be intelligent life on a large moon of a gas giant exoplanet in the “Goldilocks zone” of a red dwarf. There is also no way to know how typical the Sol system is with it’s eight planets, half of which are ice or gas giants, and half of which are small rocky planets like Earth. Most of the exoplanets we know about are gas giants like Jupiter, just because they are easier to detect. Remember, we haven’t actually “seen” any exoplanets. We only know they are there by the way their gravity affects their home stars, causing a wobble, or they are aligned with Earth such that the transit of the planet between Earth and its star causes the star to flicker. Small, rocky planets like Earth are just harder to find. So there may be lots of them, or not. We just don’t know, yet.
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This is completely correct. The Big Bang model suggests that all structures in the Colorado Broncos Rockies Avalanche Nuggets logo shirt, from super clusters down to dwarf galaxies are built bottom up, by the contestant merging of smaller clumps of stars, gas and dark matter. The statistics and nature of this merging process is at the heart of modern cosmology and can be used to discriminate against different types of dark matter and different idea about how galaxies form. The currently favored idea is that the smallest clump that can be made by direct collapse after the Big Bang is about the size of an earth – galaxies are built as clumps of this size merge to make bigger and bigger clumps. Some of these mergers are quite violent and stars can be flung to great distances like when an astroid strikes a planet- blobs of debris can be shot into outer space. Rogue stars are the galactic debris that’s wandering though space trying to get back to the galaxy that expelled it, but can’t (necessarily). The nature if the rogue star population depends on the merger history of the Milky Way. We don’t know this exactly but we can make some inferences. The Milky Way galaxy shows no real signature of a merger (like a bulge of stars). In fact it’s relatively thin disc can rule out a recent big merger. Thus the rogue stars that populate our “halo” would have to be old, dim red stars having formed along time ago. This is consistent with a lack of any strong UV emission (which comes from young hot stars) in the halo (although the brightness (or density) of these rogue stars is just barely detectable.)
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