Globular Cluster Messier 30

Messier 30
Messier 30: Image taken by Hubble Space Telescope from 2009 [262]


The globular cluster M 30 was discovered by Charles Messier in August 1764. He described it as «a nebula ... difficult to see in an ordinary 3.5-foot telescope ... It's round and I didn't see a star here, observed with a good Gregorian telescope at 104x.» It was probably Wilhelm Herschel who was able to resolve the globular cluster into single stars for the first time in 1783. He described it as follows: «Brilliant ... with two rows of stars, 4 or 5 in a line, which probably belong to them.» [4] These two rows of stars can be seen nicely on the photo from the Hubble Space Telescope in Fig. 1.

Physical Properties

On Simbad one finds a distance measurement of 7000 pc (22'800 light years) and a radial speed of 185 km/s in our direction. The cluster consists of several hundred thousand stars and measures about 90 light years in diameter. [145, 262]

Blue Stragglers
Blue Stragglers: Different birth processes. by star collision (above) and by «vampirism» (below) [262]

Stars in globular clusters are usually very old, around 12-13 billion years. However, some stars in a globular cluster are much younger than the average and seem to have been left behind by the other stars, which followed the course of stellar evolution and became red giants, so-called «blue stragglers». Such stars have been known since the 1950s, but the history of their formation remained unclear for a long time.

Francesco Ferraro from the University of Bologna published a study in 2009 [263] in which 44 high-resolution photos were examined with the Hubble space telescope. According to this study, the «blue stragglers» came about through star collisions or through a process sometimes called «vampirism». The newly formed stars are heavier than the others and are concentrated in the center of the globular cluster.

It is believed that M 30 went through a major «star collapse» a billion or two years ago, in which stars were thrown towards the center, which led to a rapid increase in star density. On the one hand, this led to an increase in star collisions and, on the other hand, favored the formation of binary systems in which one star practically sucked the other away. [262]

«Revised New General Catalogue and Index Catalogue» Dr. Wolfgang Steinicke, 2021 [277]
DesignationNGC 7099
TypeGCL (V)
Right Ascension21h 40m 22.0s
Declination-23° 10' 43"
Diameter12.00 arcmin
Visual magnitude6.9 mag
Dreyer Description!, globular, B, L, lE, gpmbM, st 12…16
IdentificationM 30, GCL 122, ESO 531-SC21

Finder Chart

The globular cluster M 30 is located in the constellation Capricornus, only 23 arc minutes from the 5.2 mag bright star 41 Capricorni. The best observation time is July to October. Then the constellation is highest above the southern horizon at night.

Chart Messier 30
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]


4«Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System» by Robert Burnham; Dover Publications, Inc.; Voume I: ISBN 0-486-23567-X; Volume II: ISBN 0-486-23568-8; Volume III: ISBN 0-486-23673-0
145SIMBAD astronomical database;
149SkySafari 6 Pro, Simulation Curriculum;
160The STScI Digitized Sky Survey;
262Vampires and collisions rejuvenate stars; (2021-02-08)
263«Two distinct sequences of blue straggler stars in the globular cluster M30» F. R. Ferraro, G. Beccari, E. Dalessandro, B. Lanzoni, A. Sills, R. T. Rood, F. Fusi Pecci, A. I. Karakas, P. Miocchi, S. Bovinelli; Published on the 24th December 2009 issue of Nature; arXiv:1001.1096; DOI:10.1038/nature08607
277«Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; (2021-02-17)