Matthew’s Blog

December 3, 2008

History of the Universe 4 - Formation of the Galaxies.

Filed under: astronomy — Tags: , , , — admin @ 12:31 pm

HISTORY OF THE UNIVERSE 4 - FORMATION OF THE GALAXIES.

The first generations of stars formed in clusters of a few million stars. By the time the universe was a billion years old gravity was pulling these clusters together forming larger groups of billions of stars. The first galaxies were born.

The universe was a fraction of it’s present size, so the forming galaxies collided more often than they do today. Small clusters merged forming larger collections of stars. Black holes formed in the centre of the clusters occasionally exploding into activity during a merger or collission. Huge amounts of energy were released producing what we know today as quasars.

The early universe was dynamic and chaotic. Collisions, explosions, new stars forming at a far greater rate than they do today. Through it all, stars were making heavy elements out of Hydrogen and then exploding. The concentration of the all important heavy elements continued to increase.

The expansion continued and by the time the universe was three billion years old things had settled down. The galaxies had grown, now containing hundreds of billions of stars. The expansion had caused galaxies to move further apart so mergers and collisions were less frequent. The universe had outgrown it’s tempestuous youth and was taking on the more mature form that we are familiar with today.

The gravitational attraction between the galaxies was trying to draw them together but the expansion of the universe was tending to pull them apart. A tug-of-war developed between the two forces resulting in a slow down of the expansion. The slow down was such that the universe might eventually stop expanding and collapse in on itself. While this process might take hundreds of billions of years it seemed that the fate of the universe was sealed.

The universe was not going give up. It would not return to the nothingness from which it came. It was about to play it’s trump card, hidden within the very fabric of space itself was a mysterious force which was about to be unleashed. This force would completely change the future of the universe.

To be continued. Check back in a few days or better still, subscribe to the RSS feed and have new posts delivered to your desktop.

© Matthew Wallace 2008

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November 6, 2008

Square Kilometre Array 2 - Major Science Goals.

Filed under: astronomy — Tags: , , , , — admin @ 1:04 pm

THE SQUARE KILOMETRE ARRAY 2 - MAJOR SCIENCE GOALS.

The sensitivity and wavelength range of the SKA are ideal to investigate the vast clouds of hydrogen that filled the universe in the darkness between the fading of the big bang fireball and the formation of the first stars.

Virtually nothing is known about this mysterious era because the hydrogen clouds emitted no light. The processes that formed the first stars can only be guessed at. The SKA however does not work with light but with radio waves and as it happens the clouds of Hydrogen emitted radio waves of known wavelength. Although the radio waves are unbelievably weak, having traveled over 13 billion light years, the SKA is powerful enough to receive and monitor the movement of these clouds.

The SKA should tell us about the currents and winds of the dark ages of the universe and how these forces produced the first stars and how the universe of stars and planets came to be.

Was Einstein right? So far the General Theory of Relativity has passed all tests with flying colours but will it continue to be accurate in the extreme environments of pulsars and black holes? We don’t know. The SKA will be able to tune in on these environments and measure accurately what is happening possibly opening up a new world of physical phenomena.

Galaxies are not distributed evenly through space but are arranged in a pattern – called the “large scale structure” - consisting of a network of knots, walls, and filaments. This pattern gives a lot of information about the structure and makeup of the universe. In it’s first year of operation SKA will map the Hydrogen in a billion galaxies, some of which are so distant that the light from them has taken over 9 billion years to reach us. The information gained will increase our understanding of how the present structure of the universe came to be and should give an insight into the workings of the recently discovered Dark Energy which is causing the rate of expansion of the universe to increase.

Magnetic fields are everywhere. The Earth has a magnetic field, so does the Sun and many of the planets. Galaxies, giant gas clouds, stars and many other astronomical objects have magnetic fields. Magnetism even exists between the galaxies. Because magnetism exists throughout the universe it has an important effect on the way astronomical objects form and evolve. Because of it’s amazing sensitivity the SKA will be able to map these fields and for the first time answer many questions about cosmic magnetism.

Are we alone in the universe? The SKA will be able to detect radar signals from civilisations 900 light years away, an area encompassing thousands of stars. If the SKA picks up a signal then the question of other intelligent life in the universe will be answered. If not, it may require a rethink of the whole question. Either way the SKA will address the matter in a way impossible previously.

The most exciting questions will be those we haven’t thought of yet. Radio astronomy has many fundamental discoveries to it’s credit and no doubt the SKA will add to that proud tradition. With this in mind the SKA’s versatile multi-purpose design will have the flexibility to undertake many different types of observations.

To be continued. Check back in a few days or better still, subscribe to the RSS feed and have new posts delivered to your desktop.

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October 25, 2008

Monsters in the sky - Black Holes

Filed under: astronomy — Tags: , , — admin @ 2:28 pm

A Black Hole is formed when a star larger than about 3 times the mass of the Sun runs out of fuel.

A star gets its energy by turning Hydrogen into Helium and heavier elements by a process called nuclear fusion. If you are not familiar with fusion see the short article here >>>


The energy produced by fusion creates light and heat but also creates an outward pressure which holds the star up against it’s gravity which tries to make the star collapse. It is much like the pressure of air in a balloon prevents it from collapsing. When the hydrogen in the centre of the star runs out the fusion reaction ceases as does the outward pressure caused by the reaction. There is now nothing to hold the star up and so it collapses in on itself.



As the star collapses, the density of the star increases because the same amount of matter is being squeezed into a smaller volume. This causes the gravity to increase which increases the rate of collapse. This in turn increases the density which increases the gravity which increases the rate of collapse which increases the density and so on. There is nothing to stop this process and the star virtually collapses to a point of unimaginable density called a singularity. The singularity produces intense gravitational field, so strong in fact, that nothing, not even light can escape. A black hole has formed.

If you are far enough away from the singularity it presents no danger. However as you get closer the gravity starts to draw you in. Up to a point you can simply fire your rockets and move away. But if you get too close the gravity is too strong and even an infinite amount of energy is not enough to enable you to move away. This point of no return is called the event horizon and marks the surface of the black hole. If you cross the event horizon you will be sucked into the singularity and nothing can save you. Even light would be drawn in.

To be continued. Check back in a few days or better still, subscribe to the RSS feed and have new posts delivered to your desktop.

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September 5, 2008

History of the Universe 3 - The First Stars

Filed under: astronomy — Tags: , , — 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.

 

© Matthew Wallace 2008

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September 1, 2008

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

Filed under: astronomy — Tags: , , — 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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August 27, 2008

A Little About Atoms - 6

Filed under: physics — Tags: , , , , — admin @ 11:17 am

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A LITTLE ABOUT ATOMS - 6

1. Introduction.
2. Types of Atoms.
3. Charged Atoms.
4. Plasma.
5. Nuclear Reactions - Fission.
6. Nuclear Reactions - Fusion.

NUCLEAR REACTIONS - FUSION

If Hydrogen atoms are placed under conditions of extreme pressure and very high temperature they can be forced together to produce Helium atoms.

In a practical reaction an atom of the Hydrogen isotope Deuterium and one of the Hydrogen isotope Tritium fuse to produce one atom of Helium and a neutron. Because the total mass of the Helium atom and the neutron is less than the total mass of the two Hydrogen atoms the missing mass is converted into energy.

Nuclear fusion

To date because of the high temperature and pressure involved it has not been possible to harness this reaction for the production of energy. A lot of research is being conducted and it is hoped that one day our energy needs might be met using nuclear fusion. The fuels required can be obtained from sea water and there is no radioactive waste.

Nuclear fusion also takes place in a hydrogen bomb. The energy is released in a short time resulting in a massive explosion.

Stars (including the Sun) are powered by fusion although the reactions are different to the one discussed.

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A Little About Atoms - 5

Filed under: physics — Tags: , , — admin @ 11:17 am

A LITTLE ABOUT ATOMS - 5

1. Introduction.
2. Types of Atoms.
3. Charged Atoms.
4. Plasma.
5. Nuclear Reactions - Fission.
6. Nuclear Reactions - Fusion.

NUCLEAR REACTIONS - FISSION

Atoms such as Uranium and Plutonium have large numbers of protons and neutrons in their nuclei. This makes the nucleus unstable. A small disturbance to the nucleus such as the addition of an extra neutron causes the nucleus to vibrate and break apart. This is called nuclear fission.

If you were to note the mass of the original nucleus before fission and then add up the masses of all the pieces after fission you would find that the total mass after fission is less than the total mass before fission. This missing mass is turned into large amounts of energy. This is the energy that powers nuclear reactors and atom bombs.

Splitting a Uranium atom

Assume we have an atom of Uranium 235, that is it has 92 protons and 143 neutrons in the nucleus. If we add an extra neutron we create Uranium 236 which is unstable. The nucleus vibrates and splits in two creating two new nuclei of approximately equal mass. In addition three neutrons are also produced. As mentioned before the total mass of the final products is less than the mass of the U235 and the initial neutron resulting in release of energy.

You will notice that the reaction was started with one neutron and three neutrons were produced in the reaction. Each of these resulting neutrons can split another nucleus. One nucleus can split three nuclei which can split nine nuclei which can split 27 and so on. In a very short time large numbers of nuclei become involved releasing huge amounts of energy. This is called a chain reaction.

Depending on how the reaction is set up the reaction can be made to proceed quickly with a rapid, explosive release of energy as in an atom bomb or the reaction can proceed much more slowly as in a nuclear reactor resulting in the energy being released over a longer period of time in a controlled fashion.

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A Little About Atoms - 4

Filed under: physics — Tags: , , , — admin @ 11:17 am

A LITTLE ABOUT ATOMS - 4

1. Introdution.
2. Types of Atoms.
3. Charged Atoms.
4. Plasma.
5. Nuclear Reactions - Fission.
6. Nuclear Reactions - Fusion.

PLASMA

Neutral Hydrogen atoms.

Imagine a cloud of Hydrogen gas. Further imagine that the Hydrogen atoms have been ionised, that is the electrons have been removed from their orbits around the nucleus ( a proton) and are moving through the cloud seperately from the protons. We have a mixture of independently moving protons and electrons. This is called a plasma.

Hydrogen plasma.

Because electrons are 2000 times less massive than protons it is easier to cause them to move through the plasma. Large clouds of electrons can be made to move in unison by electric or magnetic fields in the plasma. Such a coordinated movement of electrons constitutes an electric current. Unlike a gas, a plasma will readily conduct an electric current.
electrons flowing in unison through a plasma

Electrons flowing in unison through the plasma creating an electric current.

Plasmas are also affected by magnetic fields. The plasma will flow along magnetic field lines as illustrated by this image of a magnetic loop on the Sun.

plasma flowing along magnetic field lines on the Sun.

IMAGE CREDIT: TRACE TEAM, NASA.

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A Little About Atoms - 3

Filed under: physics — Tags: , , , , — admin @ 11:16 am

A LITTLE ABOUT ATOMS - 3

1. Introduction
2. Types of Atoms.
3. Charged Atoms.
4. Plasma.
5. Nuclear Reactions - Fission.
6. Nuclear Reactions - Fusion.

CHARGED ATOMS

Under conditions like we have on Earth it is usual for atoms not to have an electric charge. The number of positively charged protons equals the number of negatively charged electrons so the amount of positive charge is exactly balanced by the amount of negative charge. The positive and negative charges cancel out leaving the atom without a charge.
uncharged helium atom

Uncharged helium atom

Consider the Helium atom on the left. Two protons balance out the charge of the two electrons and the atom overall has no charge.
Assume that for some reason that one of the electrons is removed as shown on the next diagram down.
The atom now has two positive charges due to the two protons but only one negative charge because it now has only one electron. One positive charge is cancelled out by one negative charge but the other positive charge has no negative charge to cancel it so the atom has one overall positive charge. A charged atom is called an ion, in this case the atom is a positive ion as it has a positive charge.

charged helium atom

Charged helium atom

We can use the same reasoning in the case of a Hydrogen atom which gains an electron. In this case the atom has an overall negative charge because it has more electrons than protons, and is called a negative ion.
Material made up of charged atoms or ions is said to be ionised.

uncharged hydrogen atom

Uncharged hydrogen atom

charged hydrogen atom

Charged hydrogen atom

It is not only Hydrogen and Helium that can become ionised, any atom under the right conditions can gain or loose electrons and become charged.
On Earth charged atoms are not common but in most of the universe the majority of matter is ionised. Hydrogen between the stars, much of the material of stars and the upper atmosphere of planets (including the Earth) is ionised. The vast clouds of glowing gas seen in the photo of the Orion Nebula are clouds of Hydrogen ionised by ultra-violet radiation from new stars imbedded in the nebula.
cloud of ionised gas - orion nebula

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A Little About Atoms - 2

Filed under: physics — Tags: , , , — admin @ 11:16 am

A LITTLE ABOUT ATOMS - 2

1. Introduction.
2. Types of Atoms.
3. Charged Atoms.
4. Plasma.
5. Nuclear Reactions - Fission.
6. Nuclear Reactions - Fusion.

TYPES OF ATOMS

hydrogen atom

Hydrogen atom

The simplest atom is Hydrogen consisting of a proton in the nucleus and an electron orbiting it. It is also the most abundant atom in the universe making up some 75% of ordinary matter.
Next is another form of Hydrogen called Deuterium. It has one proton and one neutron. It is still Hydrogen because it has one proton, the number of protons determine which element it is, but the extra neutron makes it heavier than normal Hydrogen. For this reason it is sometimes called Heavy Hydrogen. Note that the charges of the electron and the proton balance each other out, the neutrons have no effect so the whole atom has no charge.

deuterium atom

Deuterium atom

Atoms with the same number of protons but a different number of neutrons are called isotopes. Deuterium then is an isotope of Hydrogen.

A third rare form of Hydrogen is Tritium one proton and two neutrons.

The next heaviest element Helium occurs naturally in two forms – Helium 3 with two protons and one neutron and Helium 4 with two protons and two neutrons. The two protons make it Helium and the different number of neutrons makes the different isotopes. Because Helium has two protons, that is two positive charges in the nucleus, it requires two electrons to balance out the positive charge so there are two electrons in orbit around the nucleus.

helium4 atom

Helium 4 atom

Other elements are made by adding more protons. Lithium has 3 protons, Berilium 4 protons, Boron 5 protons, Carbon 6 protons and so on. In each case for an uncharged atom, the number of electrons will equal the number of protons. The number of neutrons can vary giving different isotopes.

Under conditions that we have on Earth most atoms do not have a charge as the number of electrons equals the number of protons and the positive charges on the protons are balanced out by the negative charges on the electrons.

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