HIGH MASS STARS

HIGH MASS STARS

Stars greater than 8 solar masses can fuse heavier elements like C, Ne, O, and Si.

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These are very bright, blue, and short lived during its H fusion stage on the main sequence.

HIGH MASS STARS

For Example, a star only 10 times more massive than the Sun will be on the Main Sequence for about 20 million years. Compare this to the Sun’s expected life of about 11 billion years.

HIGH MASS STARS

As it fuses heavier elements it becomes a red super giant star; e.g. Betelgeuse.

As each successively heavier element begins to fuse on the core, the previous core-element forms a ring around the new core and continues to fuse there.

Its core resembles an onion with each layer fusing a different elements.

HIGH MASS STARS

The star runs through each new element faster than the previous one because the more intense pressure needed to fuse each heavier element drives the fusion process faster.

e.g. A star of ~20 solar masses will run through its:

1. H in ~1 million years,
2. He in ~10,000 years,
3. C in ~1,000 years,
4. Ne in ~1 year,
5. O in ~3 months,
6. and Si in ~1 day.

HIGH MASS STARS

Si fuses into Fe during its last day.

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Iron too begins to fuse, but rather than giving off energy Fe absorbs energy when it fuses.

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As it does the core shrinks and the pressure increases faster and faster.

HIGH MASS STARS

As the iron core builds, the star is robbed of more and more outward pressure and the entire star begins to collapse rapidly

Fe

HIGH MASS STARS

Additionally, the Fe “soaks up” free electrons. The repulsive force between these free electrons was the last thing helping to support the dying star. This further accelerates the core’s collapse.

The core collapses at nearly light speed. The core goes from thousands of km to ~20km in less than 1/1000 of a second.

HIGH MASS STARS

At this moment one of two things happen:

1. If the star was initially between 8 and 20 solar masses, the collapse stops at ~20km.�All of the electrons have been forced into the nucleus of all of the atoms. Combining a proton and an electron creates a neutron. This object is made entirely of neutrons and is called a Neutron Star. This Neutron Star will have a mass between 1.4 and 3 solar masses.

HIGH MASS STARS

At this moment one of two things happen:�

2. If the star’s initial mass was greater than 20 solar masses, nothing can stop the core’s collapse. It condenses to a mathematical point with infinite density. This is a black hole (more on this later).

HIGH MASS STARS

In either case the core gives off so many neutrinos with so much energy that the outer parts of the star are blown away in a supernova (Type II, more on this later).

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In less than 1 second these neutrinos carry as much energy as our sun will produce over its 11 billion year life.

HIGH MASS STARS

A supernova is so large that it can be seen half way across the universe. It briefly outshines its entire parent galaxy.

HIGH MASS STARS

Supernovae create all of the elements heavier than Fe.

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These elements spread out, eventually intermingling with nebulae where new stars are born.

HIGH MASS STARS

For example, all of the gold, silver, lead, mercury, etc. on Earth was created in a supernova over 5 billion years ago.

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All of the iron in your blood right now was once in the core of a massive star and ultimately caused it to explode.