Long-term, careful observation of the rotation of galaxies confirmed that galaxies turned like a single giant wheel and not a complex collection of individual stars all in separatee free orbits around the centre of the galaxy. The only explanation is that there had to be a part of galaxy, sight unseen, that should constitute the total mass of the galaxy than just the observable shining stars.
Proving that Something Undetectable Exists
At present the distances to stars and galaxies can be calculated quite accurately and the relative positions of neighbouring galaxies can be described. A computerised calculation of stars' movements around the centre of the galaxy cannot predict the observed movements in the galaxy. This result confirms the presence of a force that has not been factored in. This dark, unseen matter must have sufficient mass to hold the stars in position, comprising the hub of a giant invisible wheel.
Predicting the Model of a Galaxy
At present it is possible to calculate the distances to stars and galaxies by analysing the spectra of their light, using Cepheid variable stars and other methods such as Fraunhofer lines. Repeated observations over time can reveal the changes in relative position of neighbouring galaxies to each other, just as the planets in our solar system were observed and predicted. A computer model of a galaxy could be constructed. A model of our solar system perfectly predicts the observed movements in the solar system. A model of a galaxy does not predict the observed movements in that galaxy. The only possible prediction is that there is unseen matter surrounding the galaxy, like an immense, invisible halo (pictured), so that, adding in the dark matter component allows the computer model to accurately predict the observed movements of that galaxy.
How can Dark Matter be Identified?
Astrophysicists commenced looking for MACHOs (Massive Astrophysical Compact Halo Objects) which had mass and could be affected by gravity. The MACHO men described how when dark matter would pass between a star and the observer on Earth, gravitational lensing would cause that star to shine twice as brightly and confirm the presence of dark matter.
Neutrinos and WIMPs
Neutrinos arise from every nuclear reaction in the universe so that they could explain some of the missing dark matter. WIMPs (Weakly Interacting Massive Particles) must be detected in deep mine shafts in order to reduce interference from other unknown particles. Spectra of light from stars compliment these particle detections and display a 3D picture of how stars and galaxies are moving in relation to each other in an observed galaxy.
The Universe Remains a Mystery
The Virgo Cluster of galaxies including our own Milky Way galaxy are rushing towards a central area which is caused by dark matter with the characteristics of WIMPs. This confirms that much of the universe is a mystery with cosmologists unable to solve all the convoluted mysteries of dark matter. Will the expansion of the universe continue for all of time? Will the universe collapse due to the vast volume of dark matter? The nature of dark matter is the key.
Sources
- Stephen Hawking's Universe, The Cosmos Explained by David Filkin, BBC Books, 1997
- Astronomy, A Beginner's Guide to the Sky at Night by Paul Sutherland, Igloo Books, 2010
Michael Manning - ' The best lack all conviction while the worst are full of passionate intensity' W.B.Yeats
