Monthly Archives: November 2015

It may have been too small but it can still go BANG

White dwarf stars like our sun do not have enough mass for a core to collapse and create a supernova. However many of these white dwarfs are circling other stars and when the companion star expels it’s outer layers as a red giant the white dwarf gets extra mass and when it has enough mass it briefly resumes the fusion process and eventually creates a white dwarf supernova. All of these supernovae are exactly the same due to the fact that they all occur when the white dwarf reaches the Chandrasekhar limit of EXACTLY 1.4 times the mass of the sun. This is very important because since we know exactly how much energy is being released when these are spotted in the universe we can determine the distance from the earth. We can tell the difference between a large supernova and a white dwarf supernova by looking at it spectrum. The spectrum will show the outer layers of the star and a large supernova will still have hydrogen as its outer layer but a white dwarf used fusion to create carbon and expelled the rest of its outer layer so we will only see mostly carbon in the spectrum.

(The Great Courses – The Life and Death of Stars)

A writer who did not know two of the greatest works of all time

The Dark Ages were known as as time before the Renaissance when Classical Works were ‘rediscovered’. This is somewhat simplistic since Alfred the Great and Charlemagne were both known to have collected as many Classical Works as they could find. But there were a large number of important works which did remain largely unknown in the Dark Ages. Jefferey Chaucer did not know about the ‘Iliad’ and the ‘Odyssey’  even though he was probably aware that there was someone named Homer.

(The Great Courses – The Medieval World)

Bigger than a planet but smaller than a star

During the formation of solar systems not all stars begin the fusion process turning hydrogen into helium. A star must have a mass of about 8% of our suns mass to be able to begin to shine. If they are smaller than that they are called brown stars but they can still have disks of matter to form planets. If a forming star has over 10 times the mass of Jupiter they can briefly fuse deuterium in helium but then they shut down. This ability to briefly fuse deuterium is what astronomers use to distinguish brown dwarfs from planets.

(The Great Courses – The Life and Death of Stars)

They beat Vasco da Gama by 2000 years

The ancient Greek historian Herodotus recorded a story that a ruler of Egypt who had some Phoenician sailors at his disposal told them to see if they could sail around Africa. The story was that they sailed south from the Red Sea and around Africa through the pillars of Hercules (straights of Gibraltar) and back to Egypt. The mission took 3 years and at one point they had to stop and grow food because they ran low on provisions. Herodotus says that he did not believe the story and one of the reasons he gave was that the people who were on this mission recorded that for a while on this mission when they were sailing west the sun was on their right side. This is exactly what would happen when they sailed south of the equator, so the reason Herodotus gives for not believing the story actually makes the story more plausible.

(The Great Courses – The Greek and Persian Wars)

A BIG bounce

When a large stars core finally collapses into a neutron star the event takes place in an instant. The core collapses and the outer layers of the star which were held in place due to the core now are pulled by gravity down where they will hit the core and bounce back up. This bouncing of the outer layers off the newly formed massive core are what cause a supernova. This process has only recently been able to be described in computer models by scientists.

(The Great Courses – The Life and Death of Stars)

Starting mass defines the entire life cycle

Our sun’s core is made up of hydrogen which is using fusion to create helium with an outer layer of hydrogen. This will continue for a total of about 10 billion years. When there is enough helium in the core the helium in the core will then start fusing into carbon but there will still be a layer of hydrogen fusing into helium above that and an outer layer of hydrogen. This faze will continue for another 1 billion years when the core will be completely carbon and the fusing will cease. In stars with 8 times the sun’s mass the fusing process can continue and the carbon core will fuse into oxygen. In large enough stars this process of fusing will continue with the oxygen fusing into neon, neon fusing into magnesium, magnesium into silicon and finally the silicon into iron which is the last element which can created by natural fusion. These large stars core will then collapse from gravity and the electrons and protons will combine and create neutrons with the result being an extremely dense neutron star since there is no electrical repulsion to keep the particles apart. Water has a density of about 1 gram per cubic centimeter but a neutron star has a density of about 100 trillion grams per cubic centimeter and has a size of about 10 kilometers in diameter.

(The Great Courses – The Life and Death of Stars)

We could learn something about building structures

The early South American civilizations learned how to build stone structures to survive earthquakes. In the Incan capitol of Cuzco there were buildings that the Spanish built facades over. When a major earthquake in 1650 occurred the Spanish facades all fell but the underlying Incan structures were still standing. After another major earthquake in 1950 the same thing happened. Modern buildings fell and all the ancient Incan structures survived.
(The Great Courses – Lost Worlds of South America)