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Stages in Star and planet Formation |
From star-stuff, to stars to us. As the
saying goes,
‘We are all made from star-stuff,’but how did we get that way?
The universe is a vast and sparsely
populated place. Even within our galaxy things are spread out. The closest star
to us is over four light years away with little else occupying the space in
between. Yet that gap is not entirely empty the space between the stars, the
interstellar medium, is filled with gas and dust at densities lower than the
vacuums we can create on Earth. This gas and dust is mostly hydrogen and
helium, some of which was left over from the big bang, but it also contains
heavier elements like oxygen, carbon, and nitrogen, formed in ancient stars
then spread out across space in the explosive event of their death.
This gas and dust can come together under
its own gravity to for slightly denser regions called giant molecular clouds
that can be seen throughout our galaxy. You can even see some of them in the
night sky with the naked eye.
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Orion's sword |
Just below the
Belt of Orion on the left is Orion’s sword, where the central region is the
Orion nebula. This massive molecular cloud complex is the birthplace of stars
and future planetary systems and yet it is a trillion times less dense than our
own atmosphere and thinner than the wispiest clouds observed on the Earth.
These clouds are so cold, just 10 degrees
above absolute zero, allowing the atoms to clump together into molecules. Winds
and turbulence in the clouds can cause bigger clumps to form in knots. Due to
the low temperatures the clumps can grow and grow, and as they acquire more
mass they attract more and more clumps. This process can take around 10 million
years eventually forming a clump so large that the pressures at the center heat
it up forming a proto-star at the heart of the collapsing cloud. These regions
are dense enough to block any optical light; millimeter and sub-millimeter
observations have helped to reveal how this process occurs searching for the
emission from the in-falling material that makes up the proto-star.
The proto-star begins gathering more dust
and gas, spinning and collapsing further. After a few million years of accretion the central
mass becomes dense enough to ignite the core, fusing hydrogen into helium.
Strong stellar winds erupt from the poles; blasting away the gas and dust of
the surrounding cloud, halting the in fall of mass to the star.
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The rings of Saturn form distinct bands of material |
That stars fate is now sealed in the mass
it managed to accumulate and is at the start of its journey along the main
sequence. Surrounding the star is a disk of accreted matter that forms the
proto-planetary disk. It is here that a stellar system can form and our journey
from star-stuff to life can begin.
The gravity of the star pulls on the
particles in the disk. As they make their journey in towards the star they hit
each other and in some cases join together forming grains. Over several
thousand years they grow in size and mass turning into pebbles and rocks
orbiting in a plane around the central star. These clump into irregular objects
forming bands around the star. Much like the structures seen in the rings
orbiting Saturn.
It not until a series of violent mergers
and collisions between these rocks, over millions of years, that large
terrestrial worlds emerge capable of holding onto any gasses to form an
atmosphere. The final fate of these strange new worlds will depend upon the
temperature and type and quantity of material in the forming region.
In the last few decades our theory of
planet formation has been taken down and shook up. With the discovery of
extra-solar giant planets in places contrary to those in our own solar system
we have been forced back to the drawing board. Determining how the surrounding
environment during formation impacts the resultant system is a major topic in
astrophysics with many groups of scientists scratching their heads and
imagining anew.
WHAT’S NEXT?
There are some great links that I found
very useful so I have included them here for you to explore.
Whispers from the cosmos -http://archive.ncsa.illinois.edu/Cyberia/Expo/bima_nav.html
National Radio Astronomy Observatory –
University of Exeter - Astrophysics group -
star formation -
NASA astrophysics – Stars –