Looking back to the beginning and beyond
Immediately after the Big Bang the temperature of the universe was hundreds of billions of degrees, so hot that any structure other than the simplest of particles could not remain intact. As soon as the particles began to combine to form atoms, the enormous temperatures would rip them apart.
A charged particle is called an ion. One second after the Big Bang the universe was filled with a ‘‘hot soup’’ of particles; protons, neutrons, electrons and photons.
Hydrogen ions are protons and have an electrical charge of +1. Electrons have an electrical charge of -1. A key property of photons of light is that they collide with and are scattered by charged particles but not by electrically neutral particles.
The vast numbers of photons in the early, dense universe couldn’t travel far before they collided with and were scattered by these charged particles. This meant that hardly any photons escaped from the universe – it was opaque. As the universe cooled, the temperature lowered sufficiently for protons and neutrons to pair up then combine with electrons to form electrically neutral and stable atoms of hydrogen, deuterium (a form of hydrogen) and helium. Because these atoms were electrically neutral, the photons in the universe did not interact with them and travelled unimpeded.
For the first time, about 380,000 years after the Big Bang, the universe shone, it went from being concealed in a fog of ions to being bright and transparent.
The gravitational force between these electrically neutral atoms, drew them together in clumps; about 150 million years after the Big Bang the temperature generated by the gravitational squeezing of these atoms within these clumps was high enough to initiate nuclear reactions and the first stars were born.
Many of these early stars ended their lives in supernova explosions. The high density of the early universe combined with the intense energy from these violent explosions blasted the electrons from the hydrogen, deuterium and helium atoms in the universe turning them back into ions. The process is called reionization. The universe was again plunged into a fog of ions.
Subsequently, new stars began to accumulate into groups, pulled by their mutual gravitational forces, to form the first galaxies. The huge number of ions in space scattered the photons emitted by these early galaxies which meant the universe remained opaque and these early galaxies were obscured.
Theory and observation show that space expands causing the galaxies to move away from each other, cooling the universe. Gradually electrons began to recombine with ions to form atoms and about one billion years after the Big Bang the ion fog fully lifted.
As a galaxy moves away, the wavelength of the light emitted becomes stretched and the further the galaxy is from us the more stretched the wavelength becomes.
The light from distant galaxies has been substantially stretched towards the red end of the spectrum, ‘‘red-shifted’’. This light can only be detected using a telescope with instrumentation sensitive to infra-red radiation.
In 2010 the European Space Agency (ESA) using its Very Large Telescope (VLT) managed to capture and analyse light from a galaxy so distant that the light had taken 13.1 billion years to reach us. At the time it was the most distant object ever detected, present just 600 million years after the Big Bang.
The galaxy detected by the VLT has the rather uninspiring name, UDFy-38135539 and is incredibly faint, it was the first observed galaxy that existed after the reionization period. Only the huge VLT and its highly sensitive instrumentation along with an exposure time of 16 hours was capable of obtaining enough light to do the measurements.
Early in 2019 the successor to the Hubble Space Telescope is due to be launched; it is called the James Webb Telescope (JWT). James Webb (1906-1992) was a visionary US government official who did much to promote space exploration.
The JWT is equipped with an extremely sensitive infra-red detector. The goal is to peer further back in time and analyse light from objects even closer to the time of the Big Bang, as part of the continuing effort to find out more about the Big Bang and perhaps learn what came before it.