P3bL6 How it all began
Key Words
Big Bang - enormous explosion which produced the Universe
Gravity - an attractive force between large objects.
Hydrogen gas - a colourless gas that has very low density.
Milky Way galaxy - the galaxy of which the Solar System is a part.
Nebulae - clouds of gas and dust.
Planet - large object that orbits a star.
Protostar - a young star which has become very hot, but fusion has not yet started.
Solar system - a star and its orbiting planets
Star - a large very hot object which releases energy due to fusion reactions.
Grade E
The beginning is a very good place to start. The beginning of the Universe has been a subject of much debate by astronomers. Many of them now believe that the Universe started at a single tiny point. All the material of the Universe was concentrated at this one point. There was an enormous explosion of energy at stunningly high temperatures, which threw all the material that there is into space. This is the Big Bang. The phrase Big Bang was first used by Sir Fred Hoyle on a radio debate. He believed that the Universe was steady state; it had always been the way it is now, and will remain so the the rest of eternity. He was very dismissive of the theory and his use of Big Bang was scathing.
However there is much evidence that convinces scientists that that is what indeed happened (nobody saw it, and if they did, they would have ended up as pork scratchings). The Big Bang event is called a singularity, as it is an event in which the Laws of Physics do not apply.
- Immediately after the Big Bang, the universe consisted of sub-nuclear particles like quarks and leptons in a high temperature soup.
- Then nuclei formed.
- Then hydrogen atoms formed as a gas, spreading out as the Universe rapidly expanded.
Gravity started to act on the cloud of gas, pulling in hydrogen until it clumped together. As gravity pulled more hydrogen in, the atoms were squashed together. Their temperature rose to the levels that gave the nuclei enough energy to fuse together. Stars were made. Under gravity, the stars gathered in large clusters called galaxies.
Grade C
Stars are formed from clouds of gas called nebulae.
Particles of dust and molecules of gas come slowly together under the force of gravity.
The process takes many millions of years to happen, although the shock waves from the explosion of a supernova may help the process.
In the case of the Solar System, it is thought that the Sun and the planets formed from a slowly spinning disc of gas and dust.
Smaller amounts of dust collect together to form planet sized objects. If these are captured by the gravity of a star, they will orbit as a planet. Smaller masses of material may get captured by gravity to form satellites (moons).
If sufficient gas and dust collects in one place, it comes together under the force of gravity. The more mass there is, the stronger the gravity, therefore more material comes in. As it comes together, the whole thing starts to heat up. This is a protostar. At this time the star is only giving off radiation in the infra red and visible light regions. If there is not sufficient material, then the whole mass will cool down again.
If there is enough material, it will get hot enough for fusion to occur. The temperatures involved have to be around 15 million degrees Celsius. The star lights.
There are many solar systems in the Universe. Our solar system is on the outer arm of a spiral galaxy called the Milky Way. Like all galaxies, it is vast, consisting of hundred of millions of stars. In the middle is thought to be a super-massive black hole that gobbles up stars.
Grade A
Dust from earlier debris is attracted together by gravity, and swirls around the forming star. Heavy materials tend to form the inner planets, which makes them rocky. Lighter materials form the outer planets, which are gas giants.
Jupiter gives out quite a large amount of energy. Some scientists think it is a star that failed to light. Certainly strange things go on there. The core is thought to be hydrogen metal.
Beyond the gas giants, there is Pluto with its moon Charon. Scientists have never agreed on what should make the definition of a planet, but many argue that Pluto is too small to be a planet. They call it a planetoid.
Scientists also think that the Moon was not a separate planetoid captured by the Earth's gravity. Instead they think that the newly formed Earth collided with another planetoid, and was smashed to pieces. The rubble reformed into the planet Earth and its Moon.
Outside the Solar System is a belt of dust and ice from which comets come. This is the Oort Belt.