Nube sorpresa attorno ad una grandissima stella
Questa nuova immagine, ottenuta usando il Telescopio per Survey del VLT (VST) all'osservatorio del Paranal di ESO, mostra il notevole super ammasso di stelle Westerlund 1 (eso1034). Quest'ammasso eccezionalmente brillante si trova a 16'000 anni-luce dalla Terra, nella costellazione di Ara (L'altare), nell'emisfero sud. Esso contiene centinaia di stelle molto massicce e brillanti, tutte dell'età di solamente qualche milione di anni - delle neonate per gli standard stellari. La nostra visione di quest'ammasso è però ostacolata dal gas e dalla polvere che impedisce alla maggior parte della luce visibile proveniente dalle stelle dell'ammasso di arrivare sulla Terra.
Attualmente, gli astronomi che studiano le immagini di Westerlund 1 provenienti da una nuova survey del cielo australe [1] hanno notato qualche cosa di inaspettato in quest'ammasso. Attorno ad una di queste stelle - nota come W26, una supergigante rossa e possibilmente la più grande stella conosciuta - hanno scoperto delle nubi luminescenti di idrogeno gassoso, mostrate in verde in quest'immagine.
Tali nubi luminescenti attorno a stelle massiccio sono molto rare, e ancora di più lo sono attorno a supergiganti rosse - questo è il primo caso di nebulosa ionizzata scoperta attorno una tale stella. W26 stessa sarebbe troppo fredda per fare risplendere il gas; gli astronomi ipotizzano che la sorgente della radiazione ionizzante possa essere costituita o da stelle blu calde situate in qualche altra parte dell'ammasso, o, in alternativa, da una compagna di W26, più debole ma molto più calda.
W26 esploderà alla fine come una supernova. La nebulosa che la circonda è molto simile alla nebulosa attorno a SN1987A, i resti di una stella che divenne una supernova nel 1987 [2]. SN 1987A è la supernova più vicina alla Terra mai osservata dal 1604 e, in quanto tale, ha dato la possibilità agli astronomi di esplorare le proprietà di queste esplosioni. Lo studio di oggetti simili a questa nuova nebulosa attorno a W26 aiuterà gli astronomi a capire i processi di perdita di massa attorno alle stelle massicce, processi che portano alla loro esplosione finale.
Note
[1] Questa fotografia costituisce una parte di una dettagliata survey pubblica di una grande frazione della Via Lattea chiamata VPHAS+. Questa survey usa la potenza del VST per cercare nuovi oggetti come giovani stelle e nebulose planetarie. Una recente fotografia spettacolare della nebulosa del gambero è stata fatta usando osservazioni provenienti dalla stessa survey.
[2] Si pensa che questa nebulosa circondasse la stella progenitrice di SN1987A prima dell'esplosione.
Link
Fotografie del telescope VST per survey
Crediti:ESO/VPHAS+ Survey/N. Wright
A proposito dell'immagine
| Identificazione: | potw1341a |
| Lingua: | it |
| Tipo: | Osservazione |
| Data di pubblicazione: | Lunedì 14 Ottobre 2013 10:00 |
| Dimensione: | 4222 x 2703 px |
A proposito delll'oggetto
| Nome: | W26, Westerlund 1 |
| Tipo: | Local Universe : Star : Evolutionary Stage : Red Supergiant Local Universe : Star : Grouping : Cluster |
| Distanza: | 15000 Anni luce |
| Constellation: | Ara |
Formati delle immagini
Coordinate
| Position (RA): | 16 47 3.24 |
| Position (Dec): | -45° 50' 44.76" |
| Field of view: | 14.98 x 9.59 arcminutes |
| Orientazione: | Il Nord è a 0.3° a sinistra della verticale |
Colori e filtri
| Banda | Telescopio |
|---|---|
| Ottico G | VLT Survey Telescope OmegaCAM |
| Ottico H-alpha | VLT Survey Telescope OmegaCAM |
| Ottico R | VLT Survey Telescope OmegaCAM |
| Infrarosso I | VLT Survey Telescope OmegaCAM |
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