| rdfs:comment | - The life of a brown dwarf can be separated into 4 different stages: 1 - formation (M class) Brown dwarfs might form in a similar way stars are created: from a cloud of gas and dust. Only that the cloud is too small. Some of them orbit around a host star, so they were created like planets. In either ways, when matter collided, it should have generated enough heat to start a nuclear reaction. If the initial temperature was high enough, it could be sufficient to start fusing hydrogen into helium. If that is the case, the brown dwarf will increase size, so that pressure and temperature will decrease below hydrogen fusing, then it will slowly contract. In this phase, the dwarf might look and behave like very dim M - type stars, they might even have flares.
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| abstract | - The life of a brown dwarf can be separated into 4 different stages: 1 - formation (M class) Brown dwarfs might form in a similar way stars are created: from a cloud of gas and dust. Only that the cloud is too small. Some of them orbit around a host star, so they were created like planets. In either ways, when matter collided, it should have generated enough heat to start a nuclear reaction. If the initial temperature was high enough, it could be sufficient to start fusing hydrogen into helium. If that is the case, the brown dwarf will increase size, so that pressure and temperature will decrease below hydrogen fusing, then it will slowly contract. In this phase, the dwarf might look and behave like very dim M - type stars, they might even have flares. 2 - deuterium fuse (L class) In this phase, a brown dwarf creates a limited amount of heat by fusing deuterium. The process does not generate too much energy. Deuterium is an isotope of hydrogen, with one proton and one neutron. Since deuterium is found more rare, it will be exhausted fast. Depending on mass, some brown dwarfs might not be able to use all their deuterium. If they are too small, internal pressures will drop fast enough, so that up to 70% of deuterium will remain unused. Larger brown dwarfs will use all (or almost all) their fuel. 3 - methane (T class) When nuclear reactions are no longer taking place, the brown dwarf is cooling gradually. As the internal heat is diminishing, surface temperature is also decreasing. At some point, temperature drops below 1000 K and methane starts to get formed in the upper atmosphere. The brown dwarf still emits a dim red light, but its spectra contains some blue, from heated methane. 4 - black object (Y class) At some point, a brown dwarf is so cold that it no longer emits visible light. It becomes like a planet, like a giant Jupiter, with a similar diameter, but with much higher mass. A brown dwarf can be directly created into M - class. However, if accretion process is slow enough and matter has time to cool itself, it might simply result a lower-class dwarf. Sub - brown dwarf is an object that has not enough mass to fuse deuterium, but looks similar. In theory, when it was created, internal temperature could be enough to sustain deuterium fusion, but pressure was not enough to maintain the process.
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