Seven Wonders of the UniverseA look at the Seven Wonders of the Universe, from the Big Bang to Superdense Stars we check out the wonders of the universe.
Who needs pyramids and hanging gardens when you can have quasars and supernovae? When it comes to wonders, the Universe holds the aces.
Spanning 30 billion light years, the Universe is amazingly big. That's not all it has got going for it. Long before the seven wonders of the ancient world had been constructed, the cosmos forged its own set of wonders, which will still be here long after humankind.
The Big Bang
The first of the seven wonders of the Universe is the birth of the Universe itself. Our cosmos emerged from a superheated cloud of subatomic particles 15 billion years ago.
The greatest explosion in cosmic history marked the Universe's birth. Before the Big Bang, there used to be nothing, completely nothing. No space, no time. That all changed about 15 billion years ago when something took place that made the three dimensions of space and one of the times that we see these days spring into existence whilst also giving rise to all the matter in the Universe.
The Death of a Star
When a star reaches the end of its existence, the result is a impressive explosion known as a supernova. When stars are involved, the bigger they are, the harder they fall. Stars are huge spheres of gas which convert hydrogen fuel into helium using nuclear fusion reactions in their cores. When the nuclear fuel ultimately dries up, the star dies. The demise of a star is a violent event, and the result is frequently a supernova, exploding so intensely that the light from the blast can be seen from Earth during the day and temporarily outshines the combined light from a whole galaxy.
Supernovae leave behind a remnant object - a neutron star, a pulsar, or a black hole. The Crab Nebula in the constellation of Taurus is the debris from a supernova which was once recorded in 1054 by Chinese astronomers. In 1987, astronomers saw a supernova explode in the Large Magellanic Cloud, a small galaxy orbiting our Milky Way. It was the first supernova visible to the naked eye since 1604. Now, with the aid of powerful telescopes, astronomers are seeing supernovae in galaxies as far away as nine billion light years, which went off when the Universe was less than half its present age.
Black Holes
If a star of sufficient mass dies, the star cools and contracts. As the star contracts, it gets increasingly dense. As the density increases, so does the gravitational attraction. When a black hole forms, the gravity is so strong that even light cannot escape its pull.
The first black hole was discovered in the early 1970s and is known as Cygnus X-1. Because black holes are black, you can't see them directly. But if a black hole orbits around another star, its strong gravity will pull material from the star and heat it to such high temperatures that it emits X-rays, which can be detected.
Great Spiral Galaxies
One hundred thousand light-years across and only a thousand light-years thick, spiral galaxies comprise hundreds of billions of stars. Our own Milky Way is a spiral galaxy in which the Sun lies about two-thirds of the way out from the centre. Just as the planets orbit the Solar System, the Sun orbits around our galaxy once every 225 million years.
Spiral arms are vast shock waves that sweep around the galaxy roughly once every two billion years, as in the case of the Milky Way. The waves squash clouds of gas and dust lying in the place of the galaxy disk, causing them to fragment and collapse into new stars. The light from every new generation of stars illuminates the waves, forming the galaxy's attractive spiral pattern. Because the spiral arms revolve much slower than the stars in the galaxy's central disk, the Sun passes through one every hundred million years or so. Some scientists have suggested that these passages could explain some of the mass extinctions of life on the Earth that punctuate the fossil record.
Gamma-Ray Bursts
Gamma-ray bursts are the biggest bangs since the Big Bang. Gamma-ray bursts (GRBs) pack as much as 100 times the blast energy of a supernova and come from galaxies at the edge of the Universe 12 billion light years away.
A single ray of gamma radiation carries 100 million times the energy of a ray of visible light. A GRB emits billions upon billions of gamma rays every second, and roughly one GRB goes off daily.
Despite their high energies, gamma rays can't penetrate our planet's atmosphere because of their chemical makeup. Consequently, GRBs were not detected until humankind ventured into space. The first burst was seen by a group of satellites jointly known as Vela, designed as watchdogs for the tell-tale gamma rays from clandestine nuclear weapons tests. In 1973, after analysing just about ten years of satellite data, a group of scientists at Los Alamos National Laboratory found that most of the bursts detected hadn't come from Earth but from outer space. The race was then on to find out what they had been.
Quasars
Quasars are the brightest objects in the Universe and emit the equivalent output of 1000 normal galaxies from an area just one millionth the size of our own Milky Way. Laying billions of light years from the Earth, they were the first objects to form in the Universe after the Big Bang.
In 1960, Jodrell Bank radio observatory detected a tiny distant radio source named simply 3C48. Later, astronomers using the five-metre optical telescope at Mount Palomar checked out 3C48, anticipating it to be a galaxy. Surprisingly, they discovered it appeared more like a star, earning it a quasi-stellar object, which later shrunk to just a quasar. Over the following years, another half dozen quasars have been detected.
Superdense Stars
Our final seven wonders items are superdense stars. When stars end their lives, they leave behind a remnant object, frequently so dense that just a teaspoon of its constituent material weighs as much as a mountain.
White dwarfs squeeze a solar mass of material into a sphere the size of the Earth. They are formed during the death of Sun-like stars, squashed to around a million times the density of water. They can be found at the centre of a planetary nebula.
Neutron stars, formed in supernovae are even denser. Made completely of neutrons, they also weigh about a solar mass but measure just 10 kilometres across. Neutron stars have been described as massive atomic nuclei because their density is analogous to the nucleus of an atom, a staggering million billion times that of water. Spinning neutron stars emit light beams from their poles, which swing around with the star as it rotates. If the Earth lies in the plane of the beams, we see the star flashing like a cosmic lighthouse, rapidly flicking on and off. We call these types of spinning neutron stars pulsars.
So that's our selection of the seven wonders of the Universe. What are your top selections for the wonders of the Universe?
