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Welcome to the presentation. BY M.H.MADAN. OUR UNIVERSE. STARS BIG BANG. STARS. A star is a massive, luminous ball of plasma . The nearest star to Earth is the Sun , which is the source of most of the energy on Earth.
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Welcome to the presentation BY M.H.MADAN
OUR UNIVERSE STARS BIG BANG
A star is a massive, luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth.
Stars spend about 90% of their lifetime fusing hydrogen to produce helium in high-temperature and high-pressure reactions near the core. Such stars are said to be on the main sequence and are called dwarf stars
After the star has consumed the helium at the core, fusion continues in a shell around a hot core of carbon and oxygen. The star then follows an evolutionary path that parallels the original red giant phase, but at a higher surface temperature. Massive stars
A star begins as a collapsing cloud of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. Once the stellar core is sufficiently dense, some of the hydrogen is steadily converted into helium through the process of nuclear fusion
Characteristics The Sun is the nearest star to Earth Almost everything about a star is determined by its initial mass, including essential characteristics such as luminosity and size, as well as the star's evolution, lifespan, and eventual fate.
Age Most stars are between 1 billion and 10 billion years old. Some stars may even be close to 13.7 billion years old—the observed age of the universe. The oldest star yet discovered, HE 1523-0901, is an estimated 13.2 billion years old.[54] The more massive the star, the shorter its lifespan, primarily because massive stars have greater pressure on their cores, causing them to burn hydrogen more rapidly. The most massive stars last an average of about one million years, while stars of minimum mass (red dwarfs) burn their fuel very slowly and last tens to hundreds of billions of years.[55][56]
According to the Big Bang model, the universe expanded from an extremely dense and hot state and continues to expand today. A common and useful analogy explains that space itself is expanding, carrying galaxies with it, like raisins in a rising loaf of bread. General relativistic cosmologies, however, do not actually ascribe any 'physicality' to space.
The term 'Big Bang' was apparently first coined by Fred Hoyle in a derisory statement seeking to belittle the credibility of the theory that he did not believe to be true.[2] Ironically, Hoyle helped considerably in the effort to figure out the nuclear pathway for building certain heavier elements from lighter ones. At any rate, after the discovery of the cosmic microwave background in 1964, and especially when its collective frequencies sketched out a blackbody curve, most scientists were fairly convinced by the evidence that some Big Bang scenario must have occurred.
History The Big Bang theory developed from observations of the structure of the universe and from theoretical considerations. In 1912 Vesto Slipher measured the first Doppler shift of a "spiral nebula" (spiral nebula is the obsolete term for spiral galaxies), and soon discovered that almost all such nebulae were receding from Earth. He did not grasp the cosmological implications of this fact, and indeed at the time it was highly controversial whether or not these nebulae were "island universes" outside our Milky Way.[3] Ten years later, Alexander Friedmann, a Russiancosmologist and mathematician, derived the Friedmann equations from Albert Einstein's equations of general relativity, showing that the universe might be expanding in contrast to the static universe model advocated by Einstein.
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