A calma antes da tempestade
Esta bela imagem mostra as galáxias NGC 799 (em baixo) e a NGC 800 (em cima) situadas na constelação da Baleia. Este par de galáxias foi observado pela primeira vez em 1885 pelo astrónomo americano Lewis Swift.
Situadas a cerca de 300 milhões de anos-luz de distância, e estando voltadas de face para nós, podemos apreciar as suas formas de maneira clara. Tal como a Via Láctea - a nossa Galáxia - estes objetos são ambos galáxias em espiral, com os característicos braços compridos que se enrolam em direção ao brilhante bojo central. Nos braços em espiral bastante proeminentes podemos observar um grande número de estrelas azuis, jovens e quentes que se formam em grupos (os pequeníssimos pontos azuis que se vêem na imagem), enquanto que no bojo central um enorme grupo de estrelas velhas, vermelhas e mais frias se amontoam numa região compacta quase esférica.
À primeira vista, estas galáxias parecem-se uma com a outra, mas na realidade há muitos detalhes diferentes. Exceptuando a diferença
óbvia em tamanho, apenas a NGC 799 tem uma estrutura em barra estendendo-se do bojo central, com os braços em espiral a sair das pontas da barra. Pensa-se que as barras galácticas actuem com um mecanismo que leva o gás dos braços em espiral ao centro, aumentando assim a formação estelar. Foi também observada uma supernova na NGC 799 em 2004, a SN2004dt.
Outra característica interessante que é diferente nas duas galáxias é o número de braços em espiral. A pequena NGC 800 tem três braços em espiral brilhantes e cheios de nodos, enquanto que a NGC 799 só apresenta dois relativamente ténues, mas largos, que começam no final da barra e se enrolam quase completamente em volta da galáxia, formando uma estrutura que lembra um anel.
Embora pela imagem pareça que estas duas galáxias coexistem em total harmonia próximo uma da outra, nada pode estar mais longe da verdade. Na realidade, podemos estar a observar a calma antes da tempestade. Embora não saibamos bem o que o futuro trará, o certo é que, normalmente, quando duas galáxias se encontram relativamente próximas uma da outra, interagem entre si durante centenas de milhões de anos por meio de distúrbios gravitacionais. Em alguns casos, apenas se dão interações menores, que provocam distorções na forma das galáxias, mas às vezes as galáxias colidem, fusionando-se e dando origem a uma única e enorme galáxia nova.
Esta imagem foi obtida com o instrumento FORS1, montado no Very Large Telescope de 8,2 metros, situado no Cerro Paranal, no Chile. A imagem é composta por várias exposições obtidas com três filtros diferentes (B, V, R).
Podemos também observar cinco asteróides - consegue encontrá-los? Os asteróides movimentaram-se entre as diferentes exposições, deixando traços coloridos na imagem.
ESO
Sobre a imagem
| Id: | potw1332a |
| Língua: | pt |
| Tipo: | Observação |
| Data de divulgação: | 12 de Agosto de 2013 às 10:00 |
| Tamanho: | 1980 x 1789 px |
Sobre o objeto
| Nome: | NGC 799, NGC 800 |
| Tipo: | Local Universe : Galaxy : Type : Spiral |
| Distância: | 300 milhão anos-luz |
| Constellation: | Cetus |
Formatos de imagens
Papéis de parede
Coordenadas
| Position (RA): | 2 2 12.31 |
| Position (Dec): | 0° 6' 3.41" |
| Field of view: | 6.60 x 5.96 arcminutes |
| Orientação: | O norte está a 180.0° à direita da vertical |
Cores e filtros
| Banda | Telescópio |
|---|---|
| Óptico B | Very Large Telescope FORS1 |
| Óptico V | Very Large Telescope FORS1 |
| Óptico R | Very Large Telescope FORS1 |
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