The NASA/ESA Hubble Space Telescope has captured an amazing new photo of the 8-billion-year-old globular cluster Messier 3.
This Hubble image shows the globular cluster Messier 3. The color image was made from separate exposures taken in the visible and ultraviolet regions of the spectrum with Hubble’s Wide Field Camera 3 (WFC3). Five filters were used to sample various wavelengths. The color results from assigning different hues to each monochromatic image associated with an individual filter. Image credit: NASA / ESA / Hubble / G. Piotto et al.
Messier 3 is located approximately 34,000 light-years from Earth in the constellation Canes Venatici.
Also known as M3, GCl 25 and NGC 5272, it has an apparent magnitude of 6.2 and can be spotted using a pair of binoculars.
This globular cluster was the first object in the Messier catalog to be discovered by the French astronomer Charles Messier himself.
Messier spotted the cluster on May 3, 1764, mistaking it for a nebula without any stars. This misunderstanding of Messier 3’s nature was corrected in 1784 when the British astronomer William Herschel was able to resolve the cluster’s individual stars.
Containing about 500,000 stars, Messier 3 is one of the largest and brightest globular clusters ever discovered.
However, what makes this cluster extra special is its unusually large population of variable stars.
New variable stars continue to be discovered in Messier 3 to this day, but so far we know of 274, the highest number found in any globular cluster by far.
At least 170 of these are of a special variety called RR Lyrae variables, which pulse with a period directly related to their intrinsic brightness.
Messier 3 also contains a relatively high number of so-called blue stragglers, which are shown quite clearly in this Hubble image.
These are blue main-sequence stars that appear to be young because they are bluer and more luminous than other stars in the cluster.
As all stars in globular clusters are believed to have formed together and thus be roughly the same age.
Only a difference in mass can give these stars a different color: a red, old star can appear bluer when it acquires more mass, for instance stripping it from a nearby star.
The extra mass changes it into a bluer star, which makes us think it is younger than it really is.
