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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.
Comparison of the night sky with the night sky of a hypothetical planet within the Milky Way 10 billion years ago, at an age of about 3.6 billion years and 5 billion years before the Sun formed. [261] Globular clusters are among the oldest objects in the Milky Way, which thus set a lower limit on the age of the Milky Way.
The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31 , M31 , and NGC 224 . Andromeda has a D 25 isophotal diameter of about 46.56 kiloparsecs (152,000 light-years ) [ 8 ] and is approximately 765 kpc (2.5 million light-years ...
Interstellar space is the physical space outside of the bubbles of plasma known as astrospheres, formed by stellar winds originating from individual stars, or formed by solar wind emanating from the Sun. [132] It is the space between the stars or stellar systems within a nebula or galaxy. [133]
The Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. [ 1 ] [ 2 ] Its central massive object is a supermassive black hole of about 4 million solar masses , which is called Sagittarius A* , [ 3 ] [ 4 ] [ 5 ] a compact radio source which is almost exactly at the galactic rotational ...
The IAU definitions of planet and dwarf planet require that a Sun-orbiting astronomical body has undergone the rounding process to reach a roughly spherical shape, an achievement known as hydrostatic equilibrium. The same spheroidal shape can be seen on smaller rocky planets like Mars to gas giants like Jupiter.
Astronomers have discovered what they believe is the biggest known batch of planet-making ingredients swirling around a young star. The diameter of this colossal disk is roughly 3,300 times the ...
Smallest known galaxy Ursa Major III: Ursa Major: 3 parsecs (9.8 light-years) Half-light radius: A Milky Way satellite dwarf galaxy. [citation needed] Largest known galaxy ESO 383-76: Centaurus: 540.89 kiloparsecs (1,764,000 light-years) 90% total B-light: Central galaxy of Abell 3571 [citation needed] Largest spiral galaxy NGC 6872: Pavo