Red Giants & Red Super Giants
Red Giants, and Red Super Giants are the two possible forms of a star after is has been deprived of hydrogen. They are large (red super giants being massive!), highly luminous and have a relatively cool surface, though have a large core temperature. They are of similar mass to our Sun, or slightly greater, and are swelling up towards the end of their lives. Our own Sun will eventually evolve into a red giant, billions of years from now. As the stars swell their surfaces cool to less than 4,000 degrees, giving rise to their red colour. They have much larger diameters than are sun too, 20 times that of ours sun. consequently, they are far more luminous, many hundreds of times that of the Sun. Super red giants are much the same as this, but on a far greater scale.
White dwarfs
White dwarfs have masses similar to that of the Sun, but diameters about as small as the Earth, so they have extremely high densities. Stars become white dwarfs after they have swollen up into red giants and lost their outer layers, forming planetary nebulae; the white dwarf is the exposed core of the star, now no longer producing energy by nuclear reactions. Although white dwarfs are very hot when they are first formed, with surface temperatures up to 100,000 degrees, being so small they are inevitably very faint. White dwarfs gradually cool and fade to a ‘black dwarf’ over the course of its life.
Black holes
Black Holes are hypothetical bodies with a gravitational field so strong that nothing, including electromagnetic radiation, can escape from it. The body is surrounded by a spherical boundary, called the ‘event horizon’, through which light can enter but not escape. As no light can escape, it appears totally black; thus it’s name. Such a gravitational field can belong to a high-density body, of relatively small mass - equal to the Sun's or less - that is compressed into a very small volume; or to a low-density body of very great mass, such as a collection of millions of stars at a galaxy's centre.
It is impossible for us to find out what there is behind the event horizon, but in some shape or form, we know that a singularity must exist. This is a point to which all of the star’s mass has collapsed which is infinitely dense and exceptionally small, this is according to relativity. An additional proposal is that the singularity causes a ‘tear’ in space-time, and so becomes a ‘bottomless pit’.
Comets, Meteors & Asteroids
Comets
At the very edge of the Solar System, in a region known as the ‘Oort Cloud’, are billions of comets. They are enormous balls of dust and ice. Most are the size of a town, but some are occasionally the size of a city. Intermittently, a comet is knocked off its course, which starts it on a journey round the Sun in a long, oval orbit.
There are three types of comet. Some travel around the Sun only once and are never seen again. Periodic comets follow the same paths again and again. There are short-period comets which orbit the Sun in less that 200years, and long-period comets which can take hundreds or thousands of years before they return.
A comet looks like a dirty snowball for most of it’s life. Though when it’s closest to the sun, it’s appearance changes. The sun’s heat turns the comet’s ice into gas and dust, which forms a tail.
Meteors & Meteorites
On its journey round the Sun, the Earth collides with millions of small fragments in space. Many of these are dust particles left behind comets. As the fragments plunge through the Earth’s atmosphere, friction makes them white hot. The result is a shooting-star, or meteor, a bright line of light that flashes for a moment across the sky. Most meteors burn up as the race towards the earth, but a few are large enough to reach the ground. These are called meteorites.
Asteroids
Asteroids are lumps of rock and metal whose paths round the Sun lie mainly between Mars and Jupiter in the ‘Asteroid Belt’.
The Big Bang, Red Shift and Universe Expansion
The Big Bang Theory is the dominant scientific theory about the origin of the universe. According to the big bang theory, the universe was created somewhere between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter in all directions…
This explosion is known as the Big Bang. At the point of this event all of the matter and energy of space was contained at one point. What existed prior to this event is completely unknown and is a matter of pure speculation. This occurance was not a conventional explosion but rather an event filling all of space with all of the particles of the embryonic universe rushing away from each other. The Big Bang actually consisted of an explosion of space within itself unlike an explosion of a bomb were fragments are thrown outward. The galaxies were not all clumped together, but rather the Big Bang lay the foundations for the universe.
The origin of the Big Bang theory can be credited to Edwin Hubble. Hubble made the observation that the universe is continuously expanding. He discovered that a galaxy’s velocity is proportional to its distance. Galaxies that are twice as far from us move twice as fast. Another consequence is that the universe is expanding in every direction. This observation means that it has taken every galaxy the same amount of time to move from a common starting position to its current position. Just as the Big Bang provided for the foundation of the universe, Hubble’s observations provided for the foundation of the Big Bang theory.
Since the Big Bang, the universe has been continuously expanding and, thus, there has been more and more distance between clusters of galaxies. This phenomenon of galaxies moving farther away from each other is known as the red shift. Red shift is the shortening of the wavelength of light waves travelling from each galaxy or star, towards the observer when the object is travelling away from the observer. This is explained that when the object moving away releases a photon, the next photon released, and the one after that will be further away than if the object was motionless. This results in an apparent decrease in the wavelength of the photons traveling towards the observer.
In addition to the understanding of the velocity of galaxies emanating from a single point, there is further evidence for the Big Bang. In 1964, two astronomers tried to detect microwaves from outer space, inadvertently discovered a noise of extraterrestrial origin. The noise did not seem to emanate from one location but instead, it came from all directions at once. It became obvious that what they heard was radiation from the farthest reaches of the universe which had been left over from the Big Bang. This discovery of the radioactive aftermath of the initial explosion lent much credence to the Big Bang theory.
Even more recently, a NASA satellite detected cosmic microwaves emanating from the outer reaches of the universe. These microwaves were remarkably uniform which illustrated the ‘homogeneity’ of the early stages of the universe. However, the satellite also discovered that as the universe began to cool and was still expanding, small fluctuations began to exist due to temperature differences. These changes verified prior calculations of the possible cooling and development of the universe just fractions of a second after its creation. These fluctuations in the universe provided a more detailed description of the first moments after the Big Bang.
The Big Bang theory provides a viable solution to one of the most pressing questions of all time. It is important to understand, however, that the theory itself is constantly being revised. As more observations are made and more research conducted, the Big Bang theory becomes more complete and our knowledge of the origins of the universe more substantial.
Although the Big Bang Theory is widely accepted, it probably will never be proved; consequentially, leaving a number of tough, unanswered questions.
’Whatever you wanted to know about the universe… nearly…’
includes: The life history of a star
Comets, meteors & asteroids
The big bang theory
Red shift & universe expansion
and much more…!
Ben Jones
Bibliography
Books
Our Universe
Comets, Asteroids and Meteors
Space
The Night Sky
Extra-terrestrial Phenomena
websites from:
www.google.co.uk
www.yahoo.co.uk
www.altavista.co.uk
