|
You are here:
BBC >
Science & Nature >
Space >
Deep Space >
Dark Matter
|
|
| WIMPs
MACHOs
Neutrinos
Highly Strung
Dark Energy
Does Dark Matter?
|
NEUTRINOS
 
Early last century, a physicist called Wolfgang Pauli invented a particle to help his sums balance. It was a tiny elementary particle, smaller than an atom with no electric charge and no mass. All this particle did was carry energy as it zipped along at the speed of light. The problem was that even if they existed, being so small and placid these particles would be very tricky to find. Pauli himself confessed, "I have done a terrible thing. I have postulated a particle that cannot be detected."
Although Pauli's particle was just made up, people took it seriously enough to integrate it into new theories in particle physics. Enrico Fermi called this enigmatic character the 'neutrino', meaning 'little neutron' in Italian. After this scientific baptism, the neutrino was accepted, even though it was still absent. The hunt was on. It took over 20 years before a particle with all the right features was spotted and the neutrino was declared alive and well.
A huge amount of neutrinos was created in the Big Bang. But they are still being created in the heart of the hottest, most energetic regions in the Universe, such as supernovae, gamma ray bursts, quasars and even stars like our Sun. They even filter down to the Earth - by the time you have read this sentence an estimated 10 million neutrinos born inside the Sun will have passed through your body. When you have finished this paragraph, the same neutrinos will already be further away than the Moon.
But what does this mean for dark matter, the missing mass of the Universe? Neutrinos can be considered missing because they're so difficult to detect, as they don't interact much with ordinary matter. But if they have no mass then how can they contribute to dark matter?
The dark matter mystery was uncovered in the same year as Pauli 'invented' neutrinos, and being mass-less they were quickly crossed off the list of potential candidates. But a groundbreaking discovery in a Japanese zinc mine in 1998 proved everyone wrong. The Super-Kamiokande project announced that they had found that a certain type of neutrino did actually have a mass, albeit a small one, placing the particle firmly in the running as a dark matter contender.
Neutrinos are known as 'hot dark matter' as they travel at the speed of light. However, they may be plentiful, but because of their extremely low mass it is estimated that only make up around 25% of the missing dark matter. So where's the rest? It's a contest between MACHOs and WIMPs.
|
|
|
|
