Life of a Star, Hr diagram and Speed of Galaxys

The Life cycle of a star:

The life cycle of a star starts with the smallest particles gravitating towards each other due to small gravitational pull (we learned that all objects that have mass have gravitational pull, even if its very small it will never be 0 if there is mass). This is known as a Stellar Nebulae. After awhile, more and more particles bind together and the pressure and temperatures increase enough for fusion to occur. The pressure and temperature increase due to the gravitational pull pulling all the particles inwards. As time goes on and Fusion increases, the forces balance creating the stable period. This will last for millions of years for stars with similar mass to our sun but for those with larger mass, it will be shorter. Over time, both stars will turn into red giants, or stars with more mass then our sun will turn into super red giants, as the lack of hydrogen present in the star is now depleted. This causes the star to compress due to the gravitational pull being the largest force, increasing in temperature and pressure rapidly, this causes fusion reactions to occur between the helium nuclei's that were created before hand. This creates more energy which create more push then pull and the star rapidly increases in size (triple of its original size). As it expands, however, the star cools and more of its light energy is given off - in return for heat. What happens next depends on the mass of the star.

For stars with similar mass to our sun, The star collapses again due to the helium nuclei's have fused together creating larger nuclei's. As it collapses it increase in temperature and pressure and is therefore able to fuse larger nuclei's. This is known as a white dwarf and they are very hot stars but lack in light. After all nuclei's are depleted, the star cools and becomes a black dwarf.

For stars with larger mass then our sun, the super red giant contracts and as it does so it becomes very unstable. This is where it becomes a super nova and explodes. As it explodes it throws dust and gas into space which will form super nebulae's in the future. Any matter remaining will form a very dense neutron star, if the neutron star has a mass approximately 3 times larger then that of our own suns then it will collapse further into a black whole.

HR Diagram Explained

To the right you can see what a HR Diagram looks like and what HR actually stands for. On the Y axis we have luminosity and on the X we have temperature. Labelled are all the stars that we have mentioned before in there stages. The basics are:

• Blue has more energy

• White

• Orange

• Red

And how the colour of the star reflects that of the surface temperatures. We can also see how the largest stars are the super giants and the smallest are the dwarfs. We can make a relative assumption that the smaller the star the more heat there is, however the less luminescent it is. What you need to remember is the general positions of each of the stars.

Calculating the Speed of the galaxies

To calculate the speed of the galaxies we use the formula below:

Change in wavelength/ relative wavelength = velocity of galaxy / speed of light

So to calculate the velocity of the galaxy we would do:

(Change in wavelength/ relative wavelength) x the speed of light

A couple of practice questions and examples are below:

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1. Example:

482 - 434 / 434 * 3*10^8 = 3317972.5 m/s or 3.32*10^7

Here to calculate the change in wavelength we must first find the difference in nanometres between our reference or the sun and the galaxy. In this case it is a simple 482 - 434 which is equal to 48. Next we divided that by the reference wave length and multiple that by the speed of light (which is constant)

The reason the answer is in m/s is because:

nm/nm * m/s cancels the nanometres out therefore all we have left is the speed of lights measurements.