Star

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star : a self-luminous gaseous spheroidal celestial body of great mass which produces energy by means of nuclear fusion reactions — Webster

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Staris a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, the brightest of which gained proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the stars in the Universe, including all stars outside our galaxy, the Milky Way, are invisible to the naked eye from Earth. Indeed, most are invisible from Earth even through the most powerful telescopes.

For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen into helium in its core, releasing energy that traverses the star’s interior and then radiates into outer space. Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the star’s lifetime, and for some stars by supernova nucleosynthesis when it explodes. Near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity (chemical composition), and many other properties of a star by observing its motion through space, its luminosity, and spectrum respectively. The total mass of a star is the main factor that determines its evolution and eventual fate. Other characteristics of a star, including diameter and temperature, change over its life, while the star’s environment affects its rotation and movement. A plot of the temperature of many stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram (H–R diagram). Plotting a particular star on that diagram allows the age and evolutionary state of that star to be determined.

A star’s life begins with the gravitational collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. When the stellar core is sufficiently dense, hydrogen becomes steadily converted into helium through nuclear fusion, releasing energy in the process. The remainder of the star’s interior carries energy away from the core through a combination of radiative and convective heat transfer processes. The star’s internal pressure prevents it from collapsing further under its own gravity. A star with mass greater than 0.4 times the Sun’s will expand to become a red giant when the hydrogen fuel in its core is exhausted. In some cases, it will fuse heavier elements at the core or in shells around the core. As the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars. Meanwhile, the core becomes a stellar remnant: a white dwarf, a neutron star, or if it is sufficiently massive a black hole.

Binary and multi-star systems consist of two or more stars that are gravitationally bound and generally move around each other in stable orbits. When two such stars have a relatively close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, such as a star cluster or a galaxy. — Wikipedia

David Darling’s Internet Encyclopedia of Science, Britannica, Columbia (Infoplease)

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Stars News -- ScienceDaily News about Stars. Read science articles and see images on the birth of monstrous stars, brown dwarfs and red giants. Consider stellar evolution and more.

  • Vast stellar nursery of Lagoon Nebula
    on April 19, 2018 at 5:09 pm

    This colorful cloud of glowing interstellar gas is just a tiny part of the Lagoon Nebula, a vast stellar nursery. This nebula is a region full of intense activity, with fierce winds from hot stars, swirling chimneys of gas, and energetic star formation all embedded within a hazy labyrinth of gas and dust. […]

  • Black hole and stellar winds form giant...
    on April 18, 2018 at 6:15 pm

    Researchers have completed an unprecedented 'dissection' of twin galaxies in the final stages of merging. The new study explores a galaxy called NGC 6240. While most galaxies in the universe hold only one supermassive black hole at their center, NGC 6240 contains two -- and they're circling each other in the last steps before crashing together. […]

  • 340,000 stars' 'DNA' interrogated in search for...
    on April 18, 2018 at 1:20 pm

    Astronomers have revealed the 'DNA' of more than 340,000 stars in the Milky Way, which should help them find the siblings of the sun, now scattered across the sky. This is the first major announcement of an ambitious survey as part of a quest to uncover the formulation and evolution of galaxies -- after the Australian-led Galactic Archaeology survey, called GALAH, commenced three years ago. […]

  • Looking for extrasolar planets: DARKNESS lights...
    on April 16, 2018 at 10:56 pm

    An international team of scientists has developed a new instrument to detect planets around the nearest stars. It is the world's largest and most advanced superconducting camera. […]

  • Once upon a time, an exoplanet was discovered
    on April 16, 2018 at 4:16 pm

    In recent history, a very important achievement was the discovery, in 1995, of 51 Pegasi b, the first extrasolar planet ever found around a normal star other than the Sun. […]