Our earth is a cosmic body. It is an insignificant
speck of dust in the universe. The universe itself is a vast infinite expanse
of space and matter. Mostly it is empty space or vacuum containing nothing
seemingly physical. In this space matter is only sparely dispersed in a fashion
and due to causes that are as yet beyond our complete understanding. The
so-called concentration of matter in space have been differentiated by the
scientists into nebulae, galaxies,
stars, planets, asteroids, comets and cosmic dusts and so on. Nebulae are
enormous masses of gaseous clouds
without any structural differentiation. Galaxies are assemblies or associations
of billions of stars in each case. All the stars in a galaxy are held together
by the force of gravitation. There are millions of galaxies each with billions of stars in our
universe. A single galaxy with its constituent stars makes a stellar system.
THE
STELLAR SYSTEM
A star system or a stellar system is a small number
of stars that orbit each other, bound by gravitational attraction. A large
number of stars bound by gravitational attraction is generally called a star
cloud or galaxy, although, broadly speaking , they are also star systems. Stars
systems are no to be confused with planetary systems, which include planets and
similar bodies. A star system of two stars is known as a binary star system .
If there are no tidal effects, no perturbation from other forces, and no
transfer of mass from one star to the other, such a system is stable, and both
stars will trace out an elliptical orbit around the center of mass of the
system indefinitely. Example of binary
system are SIRIUS, PROCYON and CYGNUS X-1, the last of which probably consists
of a star and a black hole.
A multiple star system consists of three or more
stars that appears from earth to be close to one another in the sky. This may
result from the stars actually being physically close and gravitationally bound
to each other, in which case it is a physical multiple star and this closeness
may be merely apparent in which case it is an optical multiple star(Meaning
that the stars may appear to be close to each other when viewed from planet
earth as they both seems to occupy the same point in the sky but in reality,
one star may be much farther from earth
and the other, which is not readily apparent unless one can view them from a
different angle.) Physical multiple stars are also commonly called multiple
stars or multiple star systems. Most multiple star systems are triple stars.
Systems with four or more components are less likely to occur. Multiple star
systems are triple, trinary if they contain three stars; quadruple or
quaternary if they contain four stars; quintuple or quintenary with five stars;
sextuple or sextenary with six stars; septuple or septenary with seven stars. These
systems are smaller than open star clusters, which have more complex dynamics
and typically have from 100 stars to 1000 stars. Most multiple stars systems
known are triple; for higher multiplicities, the number of known systems with
given multiplicity decreases exponentially with multiplicity. For example in the
1999 revision of TOKOVININ’S CATALOG OF
PHYSICAL MULTIPLE STARS, 551 out of 728 system described are triples. However,
because of selection effects knowledge of these statistics is very incomplete.
Multiple star systems can be divided in to two main
dynamical classes; hierarchical system which are stable and consistent
of nested orbits that don’t interact much and so each level of the hierarchy
can be treated as a two-body problem, or the trapezia, which have the
unstable strongly interacting orbits and are modeled as n-body problem,
exhibiting the chaotic behavior.
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