The next
story, I want to tell is about the star….. Why suddenly I want to talk about
that bright shining things…. The reason is that I always thought that star are
cute little thing... but the real thing is that, A star is a massive, luminous
sphere of plasma held together by its own gravity. The nearest star to Earth is
the Sun, which is the source of most of the planet's energy. Some other stars
are visible from Earth during the night, appearing as a multitude of fixed
luminous points due to their immense distance. Historically, the most prominent
stars were grouped into constellations and asterisms, and the brightest stars
gained proper names. Extensive catalogues of stars have been assembled by
astronomers, which provide standardized star designations.
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. Once the hydrogen in the core of a star is
nearly exhausted, 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, luminosity, and spectrum respectively. The
total mass of a star is the principal determinant of 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,
known as a Hertzsprung–Russell diagram (H–R diagram), allows the age and evolutionary
state of a 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. Once 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 radioactive and convective processes. The star's
internal pressure prevents it from collapsing further under its own gravity.
Once the hydrogen fuel at the core is exhausted, a star with at least 0.4 times
the mass of the Sun expands to become a red giant, in some cases fusing heavier
elements at the core or in shells around the core. The star then evolves into a
degenerate form, recycling a portion of its matter into the interstellar
environment, where it will contribute to the formation of a new generation of
stars with a higher proportion of heavy elements. 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.
I still remember the lesson when I in form 3....
Well, this is credited to Wikipedia....
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