Types of Star

The Sun in the center of our solar system is a Yellow Dwarf, these are stars that have between 0.8 to 1.2 the mass of our own sun. The name Yellow Dwarf is rather misleading, firstly our sun only appears yellow due to the light interacting with Earth’s atmosphere, it is in fact white as is the case with the majority of Yellow Dwarfs. Secondly even though our sun is referred to as a ‘dwarf’ it is in fact larger in mass that the vast majority of stars in our galaxy. The lifespan of a Yellow Dwarf in its main sequence is around 10 billion years.

These are by far the most common type of star in our galaxy. Red Dwarfs have less than 50% the mass of our own Sun, as a result they are much cooler and emit far less energy. As Red Dwarfs burn their fuel at a very slow rate their lifespan is much greater than a Yellow Dwarf, existing for hundreds of billions of years and possibly even trillions of years.

Blue Stars which are still in their main sequence have up to 20 times the mass of our sun with surface temperatures more than four times that of our Sun, they can also be up to 10,000 times more bright. Blue stars burn through their fuel at a far quicker rate than smaller stars meaning they have a lifespan of only a few million years.

Death of a Star

Stars create energy by fusing hydrogen atoms into helium in their core, at some point though the hydrogen will eventually run out signaling the beginning of the end for any star. A Yellow Dwarf such as our sun has enough hydrogen to last 10 to 12 billion years, after this point when the star has no more fuel to burn it will collapse leaving only the core remaining. At this point the star is thrown a lifeline, as the core warms up due to the pressure of its collapse it generates enough heat to begin fusing helium. The star will begin expanding to hundreds of times larger than its original size turning itself into a Red Giant. Unfortunately for the star this reprieve doesn’t last long as the helium fuel will only last around 100 million years, after this point the star will lose it’s outer layers until only the core remains. At this stage the star is now a White Dwarf (picture left), the burning embers of a dead star around the size of the Earth. It will exist in this state for billions of years until it eventually cools down.

Larger stars have a very different fate to Yellow Dwarfs, the death of these stars results in some of the largest explosions in the Universe called Supernovas (picture left). When a very large star exhausts its supply of hydrogen and helium it has enough power to continue to fuse elements in its core, so helium will be fused into carbon and oxygen, carbon and oxygen into magnesium and neon and so on through the common elements. As a result of this process the star will create layers of elements with an outer shell of hydrogen, below that helium, then carbon and so on. The star will continue this process until it creates iron in its core, as the star is unable to fuse iron it becomes unstable and collapses. The iron core will collapse from the size of Earth to only around 10 miles in diameter, the energy then rebounds causing a massive explosion that rips the star apart. In the few seconds after the supernova enough heat is generated to create even heavier elements than iron such as uranium and plutonium.

The elements thrown off by these explosions form into nebulas which are clouds of gas and other materials that go on to form more stars, planets, moons and even life itself. We ourselves are made from these elements, the iron in our blood, the calcium in our bones, we were all at one point part of star.

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Neutron Stars & Black Holes

After a Supernova the core of the star is left intact, what happens to the core all depends on how large the star was. A star with a mass of between 1.5 and 5 times larger than the Sun will form into a neutron star. As the core collapses it combines electrons with protons to form neutrons allowing gravity to force the core to become even smaller. Some neutron stars can be as small as 10 miles (16 km) in diameter and are incredibly dense, one teaspoonful of a neutron star would weigh hundreds of millions of tonnes.

Neutron Stars spin incredibly quickly, they can make hundreds of rotations per second, combine this with their intense magnetic field and neutron stars sometimes produce a beam of light. The light is caused by charged particles streaming along the axis of the magnetic field, theses types of Neutron Stars are called Pulsars.

Another type of Neutron Star is a Magnetar. These stars possess a magnetic field which is one thousand times stronger than a normal Neutron Star’s and one thousand trillion times stronger than Earth’s. The field is so strong it heats up the stars surface to 10 million C (18 million F), the temperature on the surface of the sun is only 5,500 C (10,000F).

Stars that have a mass of at least 10 times the mass of the sun do not turn into Neutron Stars, the force of the collapse of these large stars is just too great and nothing can stop gravity crushing the core into an object of infinite density and zero volume, these are known as Black Holes. The gravitational force of a Black Hole is so strong that not even light can escape from it. The point of no return for any object that strays too close to a Black Hole is called the Event Horizon, past this point any object will be pulled inside and ripped apart.

Images & Video

Pleiades or Seven Sisters star cluster

Eruptions on the surface of a star, our Sun

The red supergiant Betelgeuse (Hubble image)

Posters From Solar System Quick