01Nov2012

More Questions I’ve Asked Myself

Its a  mysterious Universe and there are many questions we all have, none moreso than the more ‘simpler’ ones so let’s look at a few answers to some quetions I’ve pondered.

How Does a Star Die?Question: How Does a Star Die?

Answer: So a star has reached middle age by fusing hydrogen into helium. Then what happens? Once a star has run out of usable hydrogen that it can convert into helium, a star then takes one of several paths.

If the star is 0.5 solar masses (half the mass of our sun), electron degeneracy pressure will prevent the star from collapsing in upon itself. Due to the age of the universe, scientists can only use computer modeling to predict what will happen to such a star. Once it has finished its active phase (hydrogen to helium), it becomes a white dwarf.

A white dwarf can come about in one of two ways; first, if the star is very small, electron degeneracy pressure simply stops the collapse of the star, it is out of hydrogen, and it becomes a white dwarf. Secondly, and more commonly, the core of the star can still be surrounded by some layers of hydrogen, which continue to fuse and cause the star to expand, becoming a red giant.

A red giant is a star in the process of fusing helium to form carbon and oxygen. If there is insufficient energy to make this happen, the outer shell of the star will shed leaving behind an inert core or oxygen and carbon – a remnant white dwarf. If enough energy is involved in the casting off of stellar casings, a nebula can form. If said white dwarf is in a binary system, it could become a type 1A supernova, but this is very rare. Instead, it is thought that a white dwarf will eventually cool to become a black dwarf – in theory because there are no white dwarfs older than the universe, black dwarfs are theoretical only because there hasn’t been enough time for one to form.

If a star that has reached the end of its productive phase is below the Chandrasekhar Limit – 1.4 times the mass of our Sun – it will become a white dwarf; over this limit, it will become a neutron star. If a star is larger than about 5 times the mass of the sun, when the hydrogen fusing stops, a supernova will take place and the rest of the material will condense into a black hole.

How Does a Star Form? Question: How does a star form?

Answer: A star is formed out of cloud of cool, dense molecular gas. In order for it to become a potential star, the cloud needs to collapse and increase in density.

There are two common ways this can happen: it can either collide with another dense molecular cloud or it can be near enough to encounter the pressure caused by a giant supernova. Several stars can be born at once with the collision of two galaxies. In both cases, heat is needed to fuel this reaction, which comes from the mutual gravity pulling all the material inward.

What happens next is dependent upon the size of the newborn star; called a protostar. Small protostars will never have enough energy to become anything but a brown dwarf (think of a really massive Jupiter). A brown dwarf is sub-stellar object that cannot maintain high enough temperatures to perpetuate hydrogen fusion to helium. Some brown dwarfs can technically be called stars depending upon their chemical composition, but the end result is the same; it will cool slowly over billions of years to become the background temperature of the universe.

Medium to large protostars can take one of two paths depending upon their size: if they are smaller than the sun, they undergo a proton-proton chain reaction to convert hydrogen to helium. If they are larger than the Sun, they undergo a carbon-nitrogen-oxygen cycle to convert hydrogen to helium. The difference is the amount of heat involved. The CNO cycle happens at a much, much higher temperature than the p-p chain cycle.

Whatever the route… a new star has formed.

The life cycle of a star is dependent upon how quickly it consumes hydrogen. For example, small, red dwarf stars can last hundreds of billions of years, while large supergiants can consume most of their hydrogen with a comparably short few million years. Once the star has consumed most of its hydrogen, it has reached its mature state. This is how a star forms.

 Question: How did Saturn’s rings form?

Answer: What are Saturn's Rings Made Of? Saturn’s rings are made of ice chunks of various sizes surrounded by Saturn’s 60 moons and moonlets!

Some of the chunks of ice, ranging in size from mere microns to several meters have been in existence since the formation of Saturn itself; while others are continuously broken down and reformed by repeated collisions with each other.

Scientists have categorized several distinct rings based on size and composition and each ring is separated by a visible gap.

The way you learned your ABC’s in Kindergarten does not apply when describing Saturn’s rings. Beginning from the innermost ring and moving progressively outward, they are not in alphabetical order.

The faint innermost ring of Saturn is the D ring followed by the C ring. Both are faint and contain no moons (that have been discovered to date). The B ring is the largest and brightest of Saturn’s rings and contains several visible gaps. The Cassini Division is the large gap that separates the Saturn’s B ring from its A ring.

The Encke Gap is located within the A ring, which contains the moon Pan. Wobbles in the A ring are caused by resonance disruptions from other orbiting moons. Recently, scientists have discovered that new ring material may be generated from Saturn’s moons. Saturn’s A ring also contains the small moon Daphnis. Several other small moonlets have been discovered in the A ring, detectable only by the visible, v-shaped disruptions they cause.

Saturn’s F ring lies outside the A ring and contains the moons Prometheus and Pandora. Janus and Epimetheus are moons special enough to have their own ring designation. The particles in this ring are generated by meteoroids hitting the surface of these two moons.

The G ring is located between the F ring and the E ring. It is very faint and is acted upon by the orbit of Mimas (contained in the E ring)

Saturn’s E ring is its wide, outermost ring filled with very fine particles that are thought to be generated by the moon Enceladus. Mimas, Tethys and Dione are the other moons contained within the E ring.

Rhea, Titan, Hyperion and Iapetus are Saturn’s largest moons and orbit the planet outside the E ring.

Why is Mars Red? Question: Why is Mars Red?

Answer: Well, the short answer is that it isn’t. For most of the planet, the red layer only covers a couple of millimeters and at its deepest, two meters.

The red color comes from various oxides of iron (hematite mostly) in very, very fine particles, and trace amounts of other elements including titanium, chlorine and sulfur.

One possible way the dust was created was by harder basalt rocks, which contain more feldspar, grinding against the softer basalt to create fine dust particles.

All of that iron had to come from somewhere: volcanoes. The best information that we have is that the surface of Mars below the red layer is made up of hardened, low viscose lava: basalt. The concentration of iron in Mars’ basalt is higher than that of Earth, which is why Earth is much less red.

And that is why Mars appears red.

 What is the North Star? Question: What is the North Star?

Answer: Aside from knowing that it was an ancient tool that mariners used to find their way across the unknown seas and is well, in the North, I am left curious.

Firstly, you might expect one of the most famous stars in the night sky to be one of the brightest, but it isn’t; not by a long shot. That honor belongs to Sirius and many less bright stars besides. The North Star shines with a humble brightness that belies its navigational importance.

Polaris, or the North Star, sits almost directly above the North Pole; therefore, it is a reliable gauge of North if you find yourself lost on a clear night without a compass. Stars that sit directly above the Earth’s North or South Pole are called Pole Stars. Interestingly, the North Star hasn’t always been, nor will it always be the Pole Star because the Earth’s axis changes slightly over time, and stars move in relation to each other over time.

You can also approximate your latitude by measuring the angle of elevation between the horizon and the North Star. There is no equivalent star in the South Pole, but Sigma Octantis comes close. It isn’t very useful for navigational purposes as it isn’t very bright to the naked eye. Instead, navigators use two of the stars in the Southern Cross, Alpha and Gamma to determine due South.

The North Star is easy to find if you can first locate the Little Dipper. The North Star lies at the end of the handle in the Little Dipper (Ursa Minor). For a point of reference, The Big Dipper (Ursa Major) lies below the little dipper and their handles point in opposite directions. The two stars in the end of the ladle of The Big Dipper point to Polaris. Also, both The Big Dipper and The Little Dipper remain in the sky all night long, rotating in relation to the Earth’s axis.

Articles Provided by Universe Today  - Katrina Cain