Subanã marrom

Comparação dos tamanhos do Sol, uma subanã marrom jovem, e Júpiter. Na medida em que aumenta a idade da subanã marrom, diminui seu tamanho e temperatura.

Uma subanã marrom é um objeto de massa planetária que não orbita uma estrela, mas não chega a ser considerado uma anã marrom devido ao fato de sua massa ser menor que 13 massas de Júpiter - critério que qualifica uma anã marrom.[1]

Anãs marrons fracassadas

As subanãs marrons são formadas pelo mesmo processo pelo qual passam as estrelas ordinárias, através do colapso de uma nuvem de gás (talvez com a ajuda da fotoerosão), e não através da acreção ou colapso do núcleo de um disco circum-estelar. Não há consenso acerca dessa distinção na formação de uma subanã marrom da formação planetária; os astrônomos se dividem entre aqueles que consideram o processo de formação parte de sua divisão na classificação, e aqueles que discordam dessa distinção.[2] Uma razão para essa discordância é o fato de que muitas vezes não é possível determinar o processo de formação: por exemplo, um planeta formado através da acreção ao redor de uma estrela pode ser ejetado para fora do sistema, passando a vagar livremente pelo espaço, e da mesma forma uma subanã marrom formada a partir do colapso de uma nebulosa vagando pelo espaço pode ser capturada por uma estrela, passando a orbitá-la.

Limite da massa mínima

A menor massa de uma nuvem de gás que poderia entrar em colapso formando uma subanã marrom é de aproximadamente 1 MJ.[3] Isso se deve ao fato de o colapso por contração gravitacional demandar perda de energia irradiada na forma de calor, processo limitado pela opacidade do gás.[4] Uma candidata a subanã marrom de 3 MJ foi descrita no artigo Dusty Disks at Bottom of IMF.

Lista de candidatas a subanãs marrons

Ver também

Referências

  1. ↑ Working Group on Extrasolar Planets - Definition of a "Planet" POSITION STATEMENT ON THE DEFINITION OF A "PLANET" (IAU)
  2. ↑ What is a Planet? Debate Forces New Definition, de Robert Roy Britt, 02 de novembro de 2000
  3. ↑ Nomenclature: Brown Dwarfs, Gas Giant Planets, and?, Brown Dwarfs, Proceedings of IAU Symposium #211, ocorrido em 20–24 de maio de 2002 na Universidade do Hawaii, Honolulu, Boss, A. P., Basri, G., Kumar, S. S., Liebert, J., Martín, E. L., Reipurth, B
  4. ↑ SUBSTELLAR OBJECTS IN NEARBY YOUNG CLUSTERS (SONYC): THE BOTTOM OF THE INITIAL MASS FUNCTION IN NGC 1333, Alexander Scholz, Vincent Geers, Ray Jayawardhana, Laura Fissel, Eve Lee, David Lafreni`ere, Motohide Tamura
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