Star Formation

In an attempt to consolidate my revision I will now describe the formation of a star (possibly my favourite part of this unit at the moment) without looking - corrections I make after will be made in red.... Here I go!

Stellar Nursery in the Rosette Nebula

So we start off with a stellar nebula which is a dense cloud of gas. The gas particles are attracted by gravitational forces. As they accelerate towards each other they collide and the temperature rises. The gases cluster and fragment. This is a Protostar

Eventually the cluster and fragmentation is enough for the ignition temperature to be reached and fusion can begin. If this is never reached then it is just a protostar.

The Structure of the Sun

In the main sequence a star has a core in which fusion of Hydrogen takes place (proton proton chain), a radiation layer in which x-rays and gamma rays carry energy, followed by a convection zone where plasma something something carries energy to the surface. The bigger a star is the more power it generates and the quicker it burns out.

From now on larger mass stars and slightly smaller stars like our Sun have different life cycles. I will do the smaller star life cycle first (although technically you might argue it isn't a cycle at all...)

Eventually the star will run out of Hydrogen and fusion will stop slow down. Without energy being produced, the core contracts. Now pressure in the core is more dense has increased and it's temperature has risen enough for the fusion of Helium which then causes the core to expand again creating a Red Giant.

Ancient White Dwarf Stars
in the Milky Way 

something something The Helium fusion causes larger elements but the temperatures are not high enough for these to fuse so the star collapses to form a White Dwarf

Fusion no longer takes place but it is still dectable visible at optical wavelengths for 10 to the power of 9 years, this is called a Black something Dwarf

So a larger star will form a Giant Red Super Giant (that name must be totally wrong.. It was!) which is bigger than a normal Red Giant.

Once the Helium runs out the core will collapse and the temperatures will become high enough to fuse Silicon to form Iron. The core will become too heavy to support itself and here is where something really cool happens. The core contracts so it is really really dense and then the rest of the star collapses in extremely fast. It rushes in and rebounds off of the dense core creating temperatures high enough to fuse very large elements and make elements such as gold. There is a supernova shock wave which ejects 95% of the mass. This is a supernova type two  (I have no idea what a type one is?! oh there are actually 3 types of type 1, type 1a, 1b and 1c) and as Brian would say 'it is the brightest event in the cosmos' (he likes using that word but I don't actually know exactly what it means? It means the universe!)

Pulsar Animation

What is left is an extremely dense neutron star made up of protons and electrons (rather ironically not neutrons??) Which emits radiation form its magnetic poles and if the neutron star spins it is called a pulsar which creates a lighthouse effect so our detects receive signals on and off depending on when a pole is facing us.

After time the neutron star collapses into and the continued collapse of matter a black hole is formed which is a singularity of infinite density (which is a concept I REALLY struggle with even if I do try to think of it in terms of marshmallows...). The exit velocity is the same or larger than the speed of light and since nothing can travel faster than the speed of light nothing can escape. The star is surrounded by an event horizon beyond which we cannot see anything.

And that is everything I know! After seeing a few science blogs over the last couple of days I feel slightly embarrassed by my lack of knowledge and depth. I know there must be a whole lot more - I look forward to learning it one day! I got all of my pictures from the NASA website.