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Astronomy 1 - 4
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Essay of 12 pages for the course science at AQA (Astronomy 1 - 4)
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Unit 16 - D1 - Principles of Star CreationD1 – Principles of the Star Creation
Key points:
- Giant molecular clouds (nebulae), gravitational collapse, fragmentation
(Jean’s mass)
- Internal temperature rise, initial nuclear reactions – lithium, deuterium.
- Equilibrium: outward radiation pressure balances inward gravitational
force. Protester.
- Slower evolution to main sequence.
Nebulae
A nebula is an enormous cloud of dust and gas occupying the space between
stars and acting as a nursery for new stars. Nebulae are made up of dust, basic
elements such as hydrogen and other ionized gases. Clouds of gas are common
in our galaxy and in other galaxies like ours. These clouds are called nebulae. A
typical nebula is many light – years across and contains enough mass to make
several thousand stars the size of our sun.
Gravitational Collapse (Accretion)
Gradually, at first, the mutual gravitational attraction between all the particles
and molecules in the nebula causes the cloud to collapse inwards. This process
is called accretion. The temperature of the nebula increases as it collapses. As
the cloud shrinks, its gravitational potential energy is converted to the kinetic
energy of individual gas particles falling inward. This flattening is a natural
consequence of collisions between particles in a spinning cloud.
, Jeans’ Instability
In Astrophysics, the Jeans’ instability causes the collapse of interstellar gas
clouds and subsequent star formation, named after James Jeans (British
Astrophysics). It occurs when the international gas pressure is not strong
enough to prevent gravitational collapse of a region filled with matter. If the
mass of a nebula is greater than the Jeans’ mass (mj) then a nebula will
collapse.
Fragmentation
The collapsing cloud will break up into tens.
Hundreds, or thousands of fragments. Each
fragment continues to collapse under its
own gravity. The temperature within each
fragment rises further as the gravitational
energy is converted to kinetic energy of the particles.
Protostar
A protostar is a very young star that is still gathering mass from its parent
molecular cloud. The protostar phase is the earliest one in the process of
stellar evolution. For a low-mass star (that of the Sun or lower), it lasts about
500,000 years. Within its deep interior, the protostar has lower temperature
than an ordinary star. At its centre, Hydrogen-1 is not yet fusing with itself.
Theory predicts, however, that the hydrogen isotope Deuterium fises with
Hydrogen-1, creating helium 3.
Equilibrium in a Protostar
1) Gravity pulls gas and dust inward toward the core.
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