Vai uma Via Láctea para o jantar?
Nesta Fotografia da Semana vemos o Yepun, o quarto Telescópio Principal do Very Large Telescope (VLT) do ESO, no Chile, contra o fundo colorido do plano galáctico da Via Láctea. Mas de que é constituída, de facto, a nossa Galáxia? Os ingredientes principais são estrelas, planetas, muito gás e poeira. Mistura-se tudo, liga-se com a gravidade, adiciona-se uma grande porção de matéria escura e pronto: temos uma galáxia!
Tal como as bolachas, as galáxias podem ser de todas as formas e tamanhos. A nossa Galáxia é de tamanho médio e tem a forma de um disco com braços em espiral e um halo exterior que a rodeia. Como o nosso Sistema Solar se encontra num dos braços espirais da Via Láctea, a cerca de 25 000 anos-luz de distância do centro, apenas conseguimos vemos uma pequena fração da Galáxia quando olhamos para o céu. O centro galáctico encontra-se envolvido por camadas espessas de poeira cósmica. Por detrás dessa poeira, esconde-se o buraco negro supermassivo Sagitário A*, do qual os cientistas obtiveram uma imagem pela primeira vez em 2022.
Os astrónomos estimam que a Via Láctea contenha entre 100 e 400 mil milhões de estrelas e, provavelmente, o mesmo número de planetas. Nas regiões interiores encontramos principalmente estrelas mais velhas, enquanto os braços espirais estão repletos de estrelas jovens, formadas a partir de nuvens gigantes de gás molecular e poeira situadas nestes braços. Mais para o exterior temos o halo galáctico, onde encontramos enxames globulares, compostos por estrelas velhas, bem como restos de pequenas galáxias satélite que foram desfeitas e atraídas pela força gravitacional da nossa Via Láctea.
Finalmente, há ainda um ingrediente vital que não conseguimos ver. As galáxias giram sobre si próprias tão depressa que as estrelas, o gás e a poeira, sozinhos, não as conseguem manter coesas. É aqui que entra um “ingrediente secreto”, que explica porque é que as galáxias não se desfazem: a matéria escura. Os cientistas pensam que a Via Láctea se encontra aninhada no seio de um halo gigante de matéria escura com, pelo menos, 10 vezes a massa de todas as suas estrelas. Apesar de invisível, telescópios como o VLT ajudam-nos a compreender melhor esta matéria escura, ao investigarem a forma como esta afeta a matéria cósmica que conseguimos ver.
Créditos:ESO/J. C. Muñoz-Mateos
Sobre a imagem
| Id: | potw2449a |
| Língua: | pt |
| Tipo: | Fotográfico |
| Data de divulgação: | 2 de Dezembro de 2024 às 06:00 |
| Tamanho: | 5472 x 3648 px |
Sobre o objeto
| Nome: | Milky Way, Very Large Telescope |
| Tipo: | Milky Way Unspecified : Technology : Observatory |
Formatos de imagens
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