The Big Bang (the begining of every thing)

 

What is the milky way ? 

• The name "Milky Way" refers to how the galaxy (large group of stars bound together by gravity), which contains our Solar System, appears from Earth.  

The story of the milky way

• Soon after the Big Bang, one or more minor overdensities in the universe's mass distribution gave rise to the Milky Way. Some of these overdensities served as the precursors to the globular clusters that gave rise to the oldest still-existing stars in the Milky Way. The Milky Way may have received about half of its stuff from other far-off galaxies. Nevertheless, the stellar halo of the Milky Way is currently made up of these stars and clusters. The Milky Way's mass reached a critical mass after a few billion years of the formation of the first stars, at which point it began to spin very swiftly. This caused the gaseous interstellar medium, which had a roughly spheroidal form before, to collapse into a disc due to the conservation of angular momentum.Thus, in this spiral disc, stars of later generations evolved. The Sun and the majority of young stars are seen to be within the disc.
• The Milky Way has expanded since the first stars started to form as a result of both galaxy mergers (especially early in the Milky Way's evolution) and the direct accretion of gas from the Galactic halo.Through the Magellanic Stream, the Milky Way is actively absorbing matter from a number of tiny galaxies, including two of its largest satellite galaxies, the Large and Small Magellanic Clouds. High-velocity clouds like the Smith Cloud show direct gas accretion. The Milky Way hasn't merged with any massive galaxies in the past 10 billion years, according to stellar mass, angular momentum, and metallicity in its outermost regions. Its neighbour, the Andromeda Galaxy, appears to have a more typical history, formed by more recent mergers with comparably massive galaxies. This lack of recent major mergers is rare among similar spiral galaxies.
• Recent research indicates that the Milky Way and the Andromeda Galaxy are located in the "green valley," or region, of the galaxy color-magnitude map, which is filled with galaxies transitioning from the "blue cloud" (galaxies rapidly generating new stars) to the "red sequence" (galaxies that lack star formation). As interstellar star-forming gas becomes scarce in green valley galaxies, the rate of star formation slows. Even taking into consideration the anticipated, short-term rise in the rate of star formation caused by the collision between the Milky Way and the Andromeda Galaxy, star production will normally have been extinguished in simulated galaxies with similar features in around five billion years.The Milky Way is really among the reddest and brightest spiral galaxies that are still creating new stars, according to measurements of other galaxies that are similar to our own, and it is only somewhat bluer than the bluest red sequence galaxies. 

Age and cosmological history

• The Milky Way's oldest objects, globular clusters, provide a lower bound on how ancient the Milky Way is. Nucleocosmochronology is a method for determining the ages of individual stars in the Milky Way by measuring the amount of long-lived radioactive elements like thorium-232 and uranium-238 and comparing the results to predictions of their original abundance. For CS 31082-001 and BD +17° 3248, respectively, this result in values of around 12.5 + 3 billion years and 13.8 + 4 billion years. Once a white dwarf has created, radiative cooling starts, and the surface temperature gradually decreases. An age determination can be obtained by measuring the temperatures of the coolest of these white dwarfs and comparing them to their predicted beginning temperatures. The globular cluster M4's age was calculated using this method to be 12.7 + 0.7 billion years. The oldest of these clusters has an estimated age of 12.6 billion years, with a 95 percent confidence upper limit of 16 billion years, according to the best fit estimate.
• In the Milky Way's halo, a number of individual stars have been discovered with measured ages that are very close to the Universe's total age of 13.80 billion years. A galactic halo star named HE 1523-0901 was estimated to be 13.2 billion years old in 2007. This measurement set a lower bound on the age of the Milky Way because it was the oldest object in the Milky Way at the time. This estimate was established by measuring the relative intensities of spectral lines brought on by the existence of thorium and other elements produced by the R-process using the UV-Visual Echelle Spectrograph of the Very Large Telescope. Nucleocosmochronology can be used to determine the abundances of various elemental isotopes from the line strengths in order to determine the star's age. HD 140283 is a different star that is 14.5 + 0.7 billion years old.
•   Using nucleocosmochronology, the age of stars in the galaxy thin disc has also been calculated. According on measurements of thin disc stars, the thin disc is thought to have formed 8.8+1.7 billion years ago. These data imply that the thin disc and the galactic halo underwent a gap of almost 5 billion years. The chemical signatures of thousands of stars have recently been analysed, and the results indicate that stellar formation may have decreased by an order of magnitude during disc formation, between 10 and 8 billion years ago, when interstellar gas was too hot to continue producing stars at the same rate.
• The Milky Way's satellite galaxies are not randomly scattered; rather, it appears that they formed a ring structure 500,000 light years in diameter and 50,000 light years broad as a result of a larger system collapsing. Close encounters between galaxies, like as the one the Andromeda Galaxy is anticipated to have with another galaxy in 4 billion years, rip off enormous tails of gas that, over time, can consolidate to form dwarf galaxies in a ring at any angle to the main disc.

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