- Attachment: Well, whoops I forgot this one.
- The brightest star in the night sky is “ Sirius”. It is only 8 lightyears away and it’s brightness is measured at - 1.46 Magnitude. Sirius is slightly blue in color and has a surface temperature of 9,400 Kelvin.
- Sirius is a binary star system. Called Sirius A and B. Sirius A is the “Dog Star” and Sirius B is called the “ Pup”.
- Sirius A is a 2 Solar Mass star with an expected lifetime of 1 billion years. For comparison, our Sun is 1 Solar Mass with an expected lifetime of 10 billion years.
- Sirius B is a White Dwarf star. It is much smaller, maybe only Earth-size. It is much hotter although it no longer produces nuclear fusion it is super hot and cooling off very slowly. A White Dwarf is the exposed core of a star that has died and its outer layers expanded into a planetary nebula. The core composition depends in the size and at what stage the star lost its nuclear fuel.
- A one Solar Mass White Dwarf will be mostly made of carbon because helium was the last element to fuse and it fuses into carbon. At that point gravity was not intense enough to continue nuclear fusion to heavier elements. Larger stars will fuse carbon into oxygen. Smaller stars will remain as helium White Dwarfs.
- If a star is too large it fuses all the way up to iron. Iron will not fuse and release energy or radiation. Unlike the lighter elements Iron absorbs energy when it fuses. This means the star has no radiation to hold it up against gravity. The star collapses into the core and bounces back out into a giant explosion, a supernova.
- The pressure that holds up a White Dwarf against gravity is called “electron degeneracy” . There is not nuclear fusion. It is simply that the electrons refuse to collapse into the nuclei. The material becomes very, very dense but electron pressure holds it up. If the mass is large enough and the gravity is great enough to overcome the electron’s pressure the atoms collapse into a Neutron Star or a Blackhole if the gravity is strong enough.
- The theoretical pressure that the electrons can stand is 1.4 Solar Mass. With gravity pressure greater than 1.4 Solar Mass the electrons will collapse into the protons and form a neutron core.
- Sirius B was discovered in 1844 because its orbit wobbled Sirius A indicating some mass was tugging at it in a recurring orbit. Sirius B remained unseen until 1862 when it was first spotted using a 18 ½ inch refractor telescope. It was not categorized as a White Dwarf until 1910.
- Sirius B is exactly one Solar Mass. In 2005 its diameter was measure to be 7,500 miles, slightly smaller than the Earth. Mass of the Sun, in the volume of the Earth. That makes its density 100,000 times denser than iron.
- Over 9,000 White Dwarfs have been identified. Most are smaller that one Solar Mass averaging 67% Solar Mass.
- Sirius A and B are in a 50 year orbit. We get to view their maximum separation from our point of view in 2022.
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