La calma prima della tempesta
Questa magnifica immagine ritrae le galassie NGC 799 (sotto) e NGC 800 (sopra) nella costellazione di Cetus (La balena). Questa coppia di galassie è stata osservata per la prima volta dall'astronomo americano Lewis Swift nel 1885.
Situate a una distanza di circa 300 milioni di anni-luce, la nostra vista frontale ci permette di renderci conto chiaramente della loro forma. Come la Via Lattea - la nostra galassia - questi oggetti sono entrambi galassie spirali, con caratteristici lunghi bracci che si arrotolano verso un "bulge" centrale brillante. Nei bracci prominenti un gran numero di stelle giovani, caldissime e blu si stanno formando in ammassi (i piccoli punti blu dell'immagine) mentre nel "bulge" centrale un grande gruppo di vecchie stelle fredde e rosse si concentrano in una regione quasi sferica.
A prima vista queste galassie sembrano piuttosto simili, ma il diavolo si nasconde nei dettagli. A parte la differenza ovvia di dimensione, solo NGC 799 ha una struttura a barra che si estende dal "bulge" centrale e i suoi bracci spirali si sviluppano dalla fine della barra. Si pensa che le barre galattiche siano un meccanismo che permette al gas di fluire dai bracci spirali verso il centro, aumentando la formazione stellare. Una supernova è stata osservata in NGC 799 nel 2004 ed è stata chiamata SN2004dt.
Un'altra interessante differenza è il numero di bracci spirali. La piccola NGC 800 possiede tre bracci spirali brillanti e nodosi, mentre NGC 799 ne ha solo due relativamente deboli, ma larghi. Questi iniziano alla fine della barra e si arrotolano quasi completamente attorno alla galassia formando una struttura che assomiglia ad un anello.
A prima vista sembrerebbe che questa foto rappresenti due impressionanti galassie a spirale che coesistono pacificamente, ma niente è più lontano dalla verità. Potremmo essere testimoni della calma prima della tempesta. Non sappiamo esattamente cosa ci porterà il futuro, ma tipicamente due galassie che si trovano abbastanza vicine, interagiscono sull'arco di centinaia di milioni di anni attraverso la forza gravitazionale. In alcuni casi si tratta solo di interazioni minori che causano distorsioni di forma, ma qualche volta le galassie entrano in collisione e si fondono in un'unica nuova galassia più grande.
Quest'immagine è stata ottenuta con lo strumento FORS1 sul telescopio VLT di 8.2 metri di diametro dell'ESO in cima a Cerro Paranal. Essa include esposizioni attraverso tre filtri (B, V, R). Vi si possono riconoscere anche cinque asteroidi - Riuscite a trovarli tutti? Gli asteroidi si muovono tra le diverse esposizioni lasciando una striscia colorata nell'immagine.
Crediti:ESO
Riguardo l'immagine
| Identificazione: | potw1332a |
| Lingua: | it-ch |
| Tipo: | Osservazione |
| Data di rilascio: | Lunedì 12 Agosto 2013 10:00 |
| Grandezza: | 1980 x 1789 px |
Riguardo all'oggetto
| Nome: | NGC 799, NGC 800 |
| Tipo: | Local Universe : Galaxy : Type : Spiral |
| Distanza: | 300 Milione Anni luce |
| Constellation: | Cetus |
Formati delle immagini
Coordinate
| Position (RA): | 2 2 12.31 |
| Position (Dec): | 0° 6' 3.41" |
| Field of view: | 6.60 x 5.96 arcminutes |
| Orientazione: | Il Nord è a 180.0° a destra della verticale |
Colori e filtri
| Banda | Telescopio |
|---|---|
| Ottico B | Very Large Telescope FORS1 |
| Ottico V | Very Large Telescope FORS1 |
| Ottico R | Very Large Telescope FORS1 |
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