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  • Star clusters hang like sparkling firework displays in the sky

  • making them favourite observational targets for astronomers

  • Hubble has observed its fair share of these cosmic baubles,

  • imaging and studying them to explore their secrets.

  • This new image from Hubble shows a globular cluster known as Messier 15

  • As well as containing over 100 000 old stars, this cluster hosts something dark and mysterious at its heart.

  • Hubblecast 69: What has Hubble learned from star clusters?

  • Star clusters are some of the most beautiful objects in our skies

  • Hubble has viewed many of these over the yearsbut it is not all style over substance

  • These clusters are incredibly useful to the astronomers studying them

  • What can they tell us about our Universe?

  • There are two main types of star cluster:

  • Open,

  • and Globular.

  • Most stars, including the Sun, are thought to have formed within open star clusters

  • groups of thousands of stars loosely bound together by gravity

  • destined to be spread throughout their host galaxy once the cluster matures and most of its gas disperses.

  • Globular clusters are different; they are huge balls of old stars that orbit the centres of galaxies

  • Many of them were once little galaxies, cannibalised by their larger companions over the history of the Universe.

  • Hubble has explored many globular clusters

  • The Milky Way alone has over 150 of these starry satellites, and Hubble’s sharp vision can resolve the individual stars.

  • This has allowed Hubble to explore these star clusters in unprecedented detail.

  • Hubble has produced the deepest, most detailed images ever of a galaxy outside our own: the Andromeda galaxy,

  • spotting individual star clusters and even resolving their separate stars.

  • It has detected a population of white dwarfs within NGC 6397

  • These ancient, dying stars are the dimmest stars ever seen in any globular cluster.

  • They led to the first accurate measurements of cluster ages.

  • Hubble has also spotted the largest collection of globular clusters ever found,

  • a staggering 160 000, swarming around at the heart of the galaxy cluster Abell 1689.

  • It has probed the Milky Way’s clusters to understand how different stars age at different rates,

  • and investigated why some clusters seem to host multiple generations of stars while others contain stars of mostly the same age.

  • Now, Hubble has looked towards the globular cluster Messier 15,

  • one of the oldest globular clusters known in our galaxy, at around 12 billion years old.

  • This image of Messier 15 is reminiscent of a dazzling firework display, with golden and bright blue stars swarming together across the frame.

  • Messier 15 houses a planetary nebula known as Pease 1 — making it the first globular ever known to contain one of these objects

  • Even now, only three other similar clusters have been found to host such a planetary nebula.

  • However, all it not as it seems

  • this sparkling bauble has hidden secrets

  • Astronomers studying Messier 15 with Hubble in 2002 found there to be something dark and mysterious lurking at its heart.

  • There are two possible explanations for this intriguing finding

  • It could either be a collection of dark, incredibly dense neutron stars, or a rare and exotic intermediate-mass black hole

  • Studying these unusual black holes could tell us about how such objects grow and evolve within both star clusters and galaxies.

  • Hubblecast is produced by ESA/Hubble at the European Southern Observatory in Germany.

  • The Hubble mission is a project of international cooperation between NASA and the European Space Agency.

  • www.spacetelescope.org

  • Transcribed by ESA/Hubble. Translation --

Star clusters hang like sparkling firework displays in the sky

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