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A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. [1] [2] The word is derived from the Greek galaxias (γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System.
The listed objects currently include most objects in the asteroid belt and moons of the giant planets in this size range, but many newly discovered objects in the outer Solar System are missing, such as those included in the following reference. [58]
Size (left) and distance (right) of a few well-known galaxies put to scale. The following is a list of notable galaxies.. There are about 51 galaxies in the Local Group (see list of nearest galaxies for a complete list), on the order of 100,000 in the Local Supercluster, and an estimated 100 billion in all of the observable universe.
More recently, in November 2020, over 300 million habitable exoplanets are estimated to exist in the Milky Way Galaxy. [172] When compared to other more distant galaxies in the universe, the Milky Way galaxy has a below average amount of neutrino luminosity making our galaxy a "neutrino desert". [173]
The observable universe contains as many as an estimated 2 trillion galaxies [36] [37] [38] and, overall, as many as an estimated 10 24 stars [39] [40] – more stars (and, potentially, Earth-like planets) than all the grains of beach sand on planet Earth. [41] [42] [43] Other estimates are in the hundreds of billions rather than trillions.
The find, announced Wednesday, can help explain how solar systems across the Milky Way galaxy came to be. A six-planet solar system in perfect synchrony has been found in the Milky Way Skip to ...
Compared to many extrasolar systems, the Solar System stands out in lacking planets interior to the orbit of Mercury. [ 70 ] [ 71 ] The known Solar System lacks super-Earths , planets between one and ten times as massive as the Earth, [ 70 ] although the hypothetical Planet Nine , if it does exist, could be a super-Earth orbiting in the edge of ...
Many of the stars in a galaxy have planets. At the largest scale, ... Comparison of the contents of the universe today to 380,000 years after the Big Bang, ...