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Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae [1] and, as such, form part of the Hubble sequence. Most spiral galaxies consist of a flat, rotating disk containing stars , gas and dust , and a central concentration of stars known as the bulge .
Therefore, later generations of stars formed in this spiral disk. Most younger stars, including the Sun, are observed to be in the disk. [251] [252] Since the first stars began to form, the Milky Way has grown through both galaxy mergers (particularly early in the Milky Way's growth) and accretion of gas directly from the Galactic halo. [252]
On the right of the Hubble sequence diagram are two parallel branches encompassing the spiral galaxies. A spiral galaxy consists of a flattened disk, with stars forming a (usually two-armed) spiral structure, and a central concentration of stars known as the bulge. Roughly half of all spirals are also observed to have a bar-like structure, with ...
Named after Hindu deities, the star streams appear to be the remnants of two galaxies that merged with an early version of the Milky Way between 12 billion and 13 billion years ago when the first ...
When a galaxy forms, it has a disk shape and is called a spiral galaxy due to spiral-like "arm" structures located on the disk. There are different theories on how these disk-like distributions of stars develop from a cloud of matter: however, at present, none of them exactly predicts the results of observation.
Spiral galaxies like the Milky Way contain stars, stellar remnants, and a diffuse interstellar medium (ISM) of gas and dust. The interstellar medium consists of 10 4 to 10 6 particles per cm 3, and is typically composed of roughly 70% hydrogen, 28% helium, and 1.5% heavier elements by mass.
NGC 1300, viewed nearly face-on; Hubble Space Telescope image. A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. [1] Bars are found in about two thirds of all spiral galaxies in the local universe, [2] and generally affect both the motions of stars and interstellar gas within spiral galaxies and can affect spiral arms as well.
The most powerful telescope to be launched into space has made history by detecting a record number of new stars in a distant galaxy. NASA's James Webb Space Telescope, history's largest and most ...