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Strange matter (also known as quark matter) is an ultra-dense phase of matter that is theorized to form inside particularly massive neutron stars (which are then known as "strange stars" or "quark stars"). It's theorized that neutronium is put under sufficient pressure due to the gravitation of a large neutron star, the individual neutrons break down and their constituent quarks form strange matter. Strange matter is composed of strange quarks bound to each other directly, in a similar manner to how neutronium is composed of neutrons; a strange star is essentially a single gigantic nucleon. A strange star lies between neutron stars and black holes in terms of both mass and density, and if sufficient additional matter is added to a strange star it will collapse into a black hole as well.

Some theories suggest that strange matter, unlike neutronium, may be stable outside of the intense pressure that produced it; if this is so, then small substellar pieces of strange stars (sometimes called "strangelets") may exist in space. There is some concern that ordinary matter, upon contacting a strangelet, would be compressed into additional strange matter by its gravity; strangelets would therefore be able to "eat" any ordinary matter it came into contact with, such as planets or stars. This is thought to be highly unlikely by mainstream physicists, however.

Strangelets are thought to have a net positive charge, which is neutralized by the presence of degenerate electrons extending slightly beyond the edge of the strangelet, a kind of electron "atmosphere." If a normal matter atomic nucleus encounters a strangelet, it will approach until it reaches this atmosphere at which point it will start to see the a positive electrical potential and be repelled from the strangelet. Sufficiently energetic nuclei, or neutrons (which are unaffected by electrical charges), can reach the strangelet and be absorbed; the up/down/strange quark ratio would then readjust by beta decay.

Strange matter is largely theoretical at this point, but observations released by the Chandra X-Ray Observatory on April 10 2002 detected two candidate strange stars, designated RXJ1856 and 3C58, which had previously been thought to be neutron stars. Based on the known laws of physics, the former appeared much smaller and the latter much colder than they should, suggesting that they are composed of material denser than neutronium. There has also been some evidence that quark matter may have been produced in particle accelerators at CERN in 2000.

External links:

• http://www1.msfc.nasa.gov/NEWSROOM/news/releases/2002/02-082.html
• http://press.web.cern.ch/CERN/Announcements/2000/NewStateMatter/story.html