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September 5, 2008

History of the Universe 3 - The First Stars

Filed under: astronomy — Tags: core, heavy elements, supernova — admin @ 3:23 pm

HISTORY OF THE UNIVERSE 3 - THE FIRST STARS.

After 200 million years of total darkness light returned to the universe. One by one the first generation of stars began to shine and light up the cosmos.

These were not like the stars we are familiar with, these stars were large, 100 or more times the size of the Sun. They burnt furiously turning Hydrogen into Helium in their cores releasing huge amounts of energy.

In time the Hydrogen in the core was depleted leaving behind a core rich in Helium. Such were the conditions in the core that Helium atoms began to fuse creating atoms such as Boron and Berylium. The fusion of Hydrogen continued in a layer just outside the core. While Helium was fusing to Boron and Berylium in the core, Hydrogen was being made into Helium in the layer next to the core.

Eventually the Helium was used up in the core leaving Boron and Berylium. The Hydrogen in the next layer was turned into Helium leaving a Helium rich layer. The atoms in the core started to fuse creating Carbon, Nitrogen, Oxygen, and other atoms of similar weight. The Helium in the next layer fused into Boron and Berylium and the next layer began to fuse Hydrogen into Helium. This process continued building up sucessively heavier atoms in the core with many layers of of lighter elements. The first heavy elements in the universe were being formed.

Finally Iron began to build up in the core. Unlike the elements before it, Iron atoms do not produce energy when fused – they absorb it. Iron building up in the core was like water on a fire, the energy flowing from the core stopped, the core went dead. With no more nuclear fire the core collapsed generating a shockwave that travelled out through the star and when it reached the surface it tore the star apart in a titanic explosion called a supernova. The material of the star, including the heavy elements made in the fusion reactions, was scattered throughout the universe. As more stars exploded the concentration of heavy material increased.

While the first generation of stars were dying a new generation was forming from the clouds of Hydrogen that were left over from the first generation. This new generation was different. Unlike the first it contained heavy material which affected the way these new stars developed. They were not as large as the first generation and burnt more slowly. Like the generation before them these stars turned Hydrogen into heavy elements. Eventually they too exploded increasing the concentration of heavy material.

A third generation formed and then a fourth. The concentration of elments like Carbon, Nitrogen, Oxygen and many others was building up. The universe was preparing itself for the next big step – the universe was preparing itself for life.

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September 1, 2008

The Square Kilometre Array 1 - The world’s largest telescope.

Filed under: astronomy — Tags: interferometer, radio telescope, square kilometre array — admin @ 10:41 am

THE SQUARE KILOMETRE ARRAY 1 - THE WORLD’S LARGEST TELESCOPE

The largest telescope ever built, the Square Kilometre Array (SKA), will look into the dark age of the universe, that time between the fading of the big bang fireball and the first stars.

The “Square Kilometre Array” (SKA) will be an international radio telescope with a collecting area of one million square metres - equivalent to 200 football fields - making SKA the largest radio telescope ever constructed.

The final decision on the home of the SKA is expected in 2011. Only two countries are on the short list, South Africa and Australia. Only these countries have areas that are remote yet have access to necessary services like roads and electricity. The remoteness is needed to escape the radio interference that pervades modern society which could make the SKA useless.

Such a telescope would be so sensitive that it could detect TV broadcasts coming from the nearest stars.

The SKA will use many antennas in various configurations, combining them electronically to simulate one large antenna. One configuration will be equivalent to an antenna 3000 kilometres across. It will produce the sharpest pictures of astronomical objects of any telescope.

IMAGE CREDIT : SKA COMMUNITY.

The heart of the telescope will consist of a central core of antennas with other antennas spread out over hundreds of kilometres. A few antennas will be up to 3000 kilometres away from the central core.

NOT YOUR ORDINARY TELESCOPE.
Unlike the telescopes most people are used to the SKA is not an optical telescope, that is one that works with light, but a radio telescope, one that uses radio waves.

Because the wavelength of radio waves is much longer than the wavelength of light waves, a radio telescope has to be much larger than an optical telescope.

The SKA is a special type of radio telescope called an interferometer. It electronically combines the signals from a number of antennas spread over a large area to create the effect of a radio telescope thousands of kilometres wide.

An interferometer like the SKA can see more detail than the largest optical telescope. The Square Kilometre Array will be the most advanced telescope in the world. With its huge collecting area and computer controlled electronics it will be 50 times more sensitive than any other radio telescope.

The signals from separate antennas when combined digitally by sophisticated computers will give an extremely sharp image, producing images more detailed than any possible with modern telescopes.

The computer control will make it possible for the array to look in a number of directions at once allowing for many teams of astronomers to observe at the same time

The ability of the SKA to pick up such weak signals and to produce sharp images makes it ideal for state-of-the-art investigations to answer fundamental questions about our universe and its origin.

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