Spot the difference — Hubble spies another globular cluster, but with a secret

Thousands and thousands of brilliant stars make up this globular cluster, Messier 53, captured with crystal clarity in this image from the NASA/ESA Hubble Space Telescope. Bound tightly by gravity, the cluster is roughly spherical and becomes denser towards its heart.

These enormous sparkling spheres are by no means rare, and over 150 exist in the Milky Way alone, including Messier 53. It lies on the outer edges of the galaxy, where many other globular clusters are found, almost equally distant from both the centre of our galaxy and the Sun. Although they are relatively common, the famous astronomer William Herschel, not at all known for his poetic nature, once described a globular cluster as “one of the most beautiful objects I remember to have seen in the heavens”, and it is clear to see why.

Globular clusters are much older and larger than open clusters, meaning they are generally expected to contain more old red stars and fewer massive blue stars. But Messier 53 has surprised astronomers with its unusual number of a type of star called blue stragglers.

These youngsters are rebelling against the theory of stellar evolution. All the stars in a globular cluster are expected to form around the same time, so they are expected follow a specific trend set by the age of the cluster and based on their mass. But blue stragglers don’t follow that rule; they appear to be brighter and more youthful than they have any right to be. Although their precise nature remains mysterious these unusual objects are probably formed by close encounters, possibly collisions, between stars in the crowded centres of globular clusters.

This picture was put together from visible and infrared exposures taken with the Wide Field Channel of Hubble's Advanced Camera for Surveys.The field of view is approximately 3.4 arcminutes across.

Credit:

ESA/Hubble & NASA

About the Image

Id:potw1140a
Type:Observation
Release date:3 October 2011, 10:00
Size:4131 x 4252 px

About the Object

Name:NGC 5024
Type:• Milky Way : Star : Grouping : Cluster : Globular
• X - Star Clusters Images/Videos
Distance:60000 light years

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BandWavelengthTelescope
Optical
V
606 nm Hubble Space Telescope
ACS
Optical
Pseudogreen (V+I)
Hubble Space Telescope
ACS
Infrared
I
814 nm Hubble Space Telescope
ACS

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