The globular cluster Messier 5, shown here in this NASA/ESA Hubble Space Telescope image, is one of the oldest belonging to the Milky Way. The majority of its stars formed more than 12 billion years ago, but there are some unexpected newcomers on the scene, adding some vitality to this aging population. Stars in globular clusters form in the same stellar nursery and grow old together. The most massive stars age quickly, exhausting their fuel supply in less than a million years, and end their lives in spectacular supernovae explosions. This process should have left the ancient cluster Messier 5 with only old, low-mass stars, which, as they have aged and cooled, have become red giants, while the oldest stars have evolved even further into blue horizontal branch stars. Yet astronomers have spotted many young, blue stars in this cluster, hiding amongst the much more luminous ancient stars. Astronomers think that these laggard youngsters, called blue stragglers, were created either by stellar collisions or by the transfer of mass between binary stars. Such events are easy to imagine in densely populated globular clusters, in which up to a few million stars are tightly packed together. Messier 5 lies at a distance of about 25 000 light-years in the constellation of Serpens (The Snake). This image was taken with Wide Field Channel of Hubble’s Advanced Camera for Surveys. The picture was created from images taken through a blue filter (F435W, coloured blue), a red filter (F625W, coloured green) and a near-infrared filter (F814W, coloured red). The total exposure times per filter were 750 s, 400 s and 567 s, respectively. The field of view is about 2.6 arcminutes across.

Hubble visita a Messier 5

«Descubierta una hermosa nebulosa entre la Balanza (Libra) y la Serpiente…». Así comienza la descripción de la quinta entrada del famoso catálogo de nebulosas y cúmulos estelares del astrónomo del siglo XVIII Charles Messier. A Messier le parecía difusa, redonda y sin estrellas, pero hoy en día se sabe que Messier 5 (M5) es un cúmulo globular de 100.000 estrellas o más unidas por la gravedad y agrupadas en una región de unos 165 años luz de diámetro. Se encuentra a unos 25.000 años luz de distancia. Vagando por el halo de nuestra galaxia, los cúmulos estelares globulares son antiguos miembros de la Vía Láctea. M5 es uno de los más antiguos; se estima que sus estrellas tienen unos 13 mil millones de años.
El atractivo cúmulo estelar es un popular objetivo de los telescopios terrestres. El Telescopio Espacial Hubble, instalado en una órbita baja de la Tierra el 25 de abril de 1990, también captó este impresionante primer plano que abarca unos 20 años luz cerca de la región central. En la nítida fotografía, cerca del denso núcleo (a la izquierda) las envejecidas estrellas gigantes rojas y azules así como las rejuvenecidas azules más distantes destacan en tonos amarillos y azules.

Crédito de la imagen: HST, ESA, NASA

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