| The birth of the Sun and the solar system |
|
 |
The Sun is a rather ordinary star, and it was born in the same way as stars are born around in the nebulas as happens even today.
|
|
|
| |
| How are stars formed? |
Stars arise from gigantic dust and gas clouds in the interstellar space. These may have diameters of more than one hundred light years.
The gas in the clouds is extremely thin with a mass of density around
10-23 g/cm3
Or 0.000 000 000 000 000 000 000 01 gram per cubic centimetre.
This is for us an incredibly low density. It is a vacuum much better than anything we may be able to produce here on the Earth.
What processes may be able to compress this gas to a density of mass of at least 1 g/cm3 such as we find it in the stars?
The gravitational forces between the particles would at best have taken hundreds of millions or billions of years to make stars from these clouds. Fortunately, some local condensations occur inside the large cloud. These so-called globules are dense enough for the gravitational forces to begin getting hold of them. |
| |
The innermost part of the condensations collapses during some million years to become dense objects that are called prototype stars. These yield potential gravitational energy by tightening slowly. When the gas becomes dense, the radiation is not able to pass through it.
It is as if the fog has settled down. If it is in the middle of the day, there is light everywhere, but we cannot see the Sun’s disc that gives all the light.
When the gas and the radiation start interacting in this way in the prototype star, the gas stops falling freely.
From now on things happen more slowly and the temperature and consequently also the pressure start increasing. Round this prototype star gas and dust continue to circle towards the centre in a whirl disc (also called accretion disc) and fall down on the prototype star. The mass of the prototype star therefore continues to increase. |
| |
The dust particles consist of carbon, ice, silicon compounds, iron and others. They are about 0.1 micrometer or 0.0001 millimetres large. A typical grain of dust weighs probably 10-18 kg, or 0.000 000 000 000 000 001 kg.
After further thousands, or millions of years (dependent on the mass), the centre of the prototype star has become so hot that the first nuclear reaction starts producing energy. The contraction stops rather rapidly, the surface temperature becomes relatively high and both whirl disc and the rest of the cloud of gas outside this will be blown away again. With the space telescope one has been able to take instantaneous images of such events. |
| |
|
Orion’s cloud.
Photo: NASA/STScI. |
|
Usually many stars are born from one large cloud of gas, such as Orion’s cloud.
Gradually they blow away the clouds around them, and the intense radiation makes the tiny little particles of dust evaporate. This is very clearly seen in images taken by the space telescope of the Eagle’s Cloud.
In the Eagle’s Cloud, also called M16, stars and planets are born. The dark structures in this image are gas and dust becoming stars. On the top of each of the small pillars, of which we may vaguely see rather a lot, a solar system is being born. The tip of each of these tops is larger than our solar system (measured up to and including the planet Pluto)! In addition, there are certainly hundreds of such births of stars hidden deep inside the dark fog.
|
| |
|
| The Eagle’s Cloud, M16. |
|
Certain parts of the clouds of gas and dust become so dense that they collapse. This may take several million years, but finally there is a rather dense object in the middle absorbing gas and dust from the surroundings by means of its gravitational force getting stronger and stronger.
What is absorbed moves spirally towards the prototype star in the middle. This spiral is like a rotating discus. The space telescope Hubble has for the first time made it possible to see how this takes place.
In these images we see two such whirl discs from the inside. In the middle of each one of them a star starts shining - but it is not yet a “proper” star. If instead we had seen the whirl discs from above, they would have looked like a dark discus with a shining spot in the middle. |
| |
|
| Photo: NASA/STScI. |
|
If we see the whirl discs round the future stars from above, they look like the image to the left. The dark gas and the dust move in a spiral towards the dense and constantly hotter lump in the middle.
Here we have 4 different incidents. They have not got equally far in their development. The one to the bottom left has got farther – it is soon to be a proper star.
The dark whirl disc may also make planets! It was probably from such a disc that the Earth and the other planets in the solar system came into existence. |
|
|
|
|
| |
|
|
| |
|
