Andromeda Galaxy
· INTRODUCTION
The Andromeda galaxy (/ænˈdrɒmɪdə/), additionally called Messier thirty-one, M31, or NGC 224, may be a galaxy about 780 kiloparsecs (2.5 million light-years) from Earth, and therefore the nearest major galaxy to the Milky Way. Its name stems from the realm of the Earth's sky during which it seems, the constellation of Andromeda.
The virial mass of the Andromeda galaxy is of a similar order of magnitude as that of the Milky Way, at a trillion-star lots (1012M☉). The mass of either galaxy is tough to estimate with any accuracy, however it absolutely was long thought that the Andromeda galaxy is additional large than the Milky Way by a margin of some 25% to 50%. This has been known as into question by a 2018 study that cited a lower estimate on the mass of the Andromeda galaxy, combined with preliminary reports on a 2019 study estimating a higher mass of the Milky Way. The Andromeda Galaxy has a diameter of about 220,000 light-years, making it the largest member of the Local Group at least in terms of extension, if not mass.
The number of stars contained in the Andromeda Galaxy is estimated at one trillion (1×1012), or roughly twice the number estimated for the Milky Way.
The Milky Way and Andromeda galaxies area unit expected to collide in ~4.5 billion years, merging to create a large elliptical galaxy or an oversized disc galaxy. With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier objects making it visible to the naked eye from Earth on moonless nights, even when viewed from areas with moderate light pollution.
Around the year 964, the Persian stargazer Abd al-Rahman al-Sufi represented the Andromeda galaxy, in his Book of fastened Stars as a "nebulous smear".
Star charts of that amount tagged it because the very little Cloud. In 1612, the German urologist Simon Marius gave associate degree early description of the Andromeda galaxy supported telescopic observations. The German philosopher Immanuel Kant in 1755 in his work Universal Natural History and Theory of the Heavens conjectured that the blurry spot was an island universe. In 1764, Charles Messier cataloged Andromeda as object M31 and incorrectly attributable Marius because the discoverer despite it being visible to the optic. In 1785, the stargazer Herschel noted a faint red hue within the core region of Andromeda. He believed Andromeda to be the closest of all the "great nebulae", and based on the color and magnitude of the nebula, he incorrectly guessed that it is no more than two,000 times the distance of Sirius. In 1850, William Parsons, 3rd Earl of Roses, saw and made the first drawing of Andromeda's spiral structure.
· Structure
Based on its look in light, the Andromeda Galaxy is classified as an SA(s)b galaxy in the de Vaucouleurs–Standage extended classification system of spiral galaxies. However, data from the 2MASS survey showed that Andromeda is actually a barred spiral galaxy, like the Milky Way, with Andromeda's bar oriented along its long axis.
In 2005, astronomers used the Keck telescopes to indicate that the tenuous sprinkle of stars extending outward from the galaxy is truly a part of the most disk itself. this suggests that the spiral disk of stars within the Andromeda galaxy is thrice larger in diameter than antecedently calculable. This constitutes evidence that there is a vast, extended stellar disk that makes the galaxy more than 220,000 light-years (67,000 parsecs) in diameter. Previously, estimates of the Andromeda Galaxy's size ranged from 70,000 to 120,000 light-years (21,000 to 37,000 pc) across.
The galaxy is inclined associate degree calculable 77° relative to Earth (where associate degree angle of 90° would be viewed directly from the side). Analysis of the cross-sectional shape of the galaxy appears to demonstrate a pronounced, S-shaped warp, rather than just a flat disk. A possible cause of such a warp could be fundamental interaction with the satellite galaxies close to the Andromeda galaxy. The Galaxy M33 can be liable for some warp in Andromeda's arms, though more precise distances and radial velocities are required.
· Satellites
Like the Milky Way, the Andromeda Galaxy has satellite galaxies, consisting of 14 known dwarf galaxies. The best known and most pronto discovered satellite galaxies area unit M32 and M110. Based on current proof, it appears that M32 underwent a close encounter with the Andromeda Galaxy in the past. M32 might once are a bigger galaxy that had its stellar disk removed by M31, and underwent a sharp increase of star formation in the core region, which lasted until the relatively recent past.
M110 additionally seems to be interacting with the Andromeda galaxy, and astronomers have found in the halo of the latter a stream of metal-rich stars that appear to have been stripped from these satellite galaxies.M110 will contain a dirty lane, which can indicate recent or current star formation. M32 litter population also.
In 2006, it was discovered that nine of the satellite galaxies lie in a plane that intersects the core of the Andromeda Galaxy; they are not randomly arranged as would be expected from independent interactions. This may indicate a common tidal origin for the satellites.
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