These are organized by a classification scheme developed exclusively for Cosma. More…
star : a self-luminous gaseous spheroidal celestial body of great mass which produces energy by means of nuclear fusion reactions — Webster
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
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.
Challenging existing models of black holes
on January 19, 2018 at 1:59 pm
A new study expands the scientific community's understanding of black holes in our galaxy and the magnetic fields that surround them. […]
Neutron-star merger yields new puzzle for...
on January 18, 2018 at 7:26 pm
The afterglow from the distant neutron-star merger detected last August has continued to brighten - much to the surprise of astrophysicists studying the aftermath of the massive collision that took place about 138 million light years away and sent gravitational waves rippling through the universe. New observations indicate that the gamma ray burst unleashed by the collision is more complex than scientists initially imagined. […]
Odd behavior of star reveals lonely black hole...
on January 17, 2018 at 1:56 pm
Astronomers using ESO's MUSE instrument on the Very Large Telescope in Chile have discovered a star in the cluster NGC 3201 that is behaving very strangely. It appears to be orbiting an invisible black hole with about four times the mass of the sun -- the first such inactive stellar-mass black hole found in a globular cluster and the first found by directly detecting its gravitational pull. […]
How massive can neutron stars be?
on January 16, 2018 at 2:36 pm
Astrophysicists set a new limit for the maximum mass of neutron stars: It cannot exceed 2.16 solar masses. […]
Archeology of our Milky Way's ancient hub
on January 11, 2018 at 9:29 pm
A new analysis of about 10,000 normal Sun-like stars in the Milky Way's bulge reveals that our galaxy’s hub is a dynamic environment of variously aged stars zipping around at different speeds. […]