The NASA Hubble Telescope made this beautiful picture of a cluster of stars, NGC 6441. It is located in our Galaxy, around 40,000 light years from Earth in the constellation Scorpio. The mass of this globular cluster is estimated to be around 1.6 million times that of the sun, which makes it one of the most massive and brightest globular clusters in the Milky Way. How many stars are part of the cluster is hard to estimate. The different colours of the stars in the cluster (yellow-red, white and blue) tell something about the temperature at their surface, and hence about their mass.
Interestingly, from the distribution of the individual stars in this system one can deduce that they all interact with each other by gravitational force (attraction). As we know from th spiral form of entire galaxies (which contain of course a much larger number of stars), there is usually a rotational component that results from the attracting gravitation (which is directed to the overall center of mass, sometimes in the form of a black hole) plus an initial tangential component of movement of the stars relative to each other. This is similar to what one can see on the rock’n roll dance floor, when two dancers quickly move towards each other, and then suddenly grab their hands firmly. As a result, they are unavoidibly forced into a quick spin around each other.
With the star cluster NGC 6441, however, there is no indication what so ever of an internal rotational movement. This means that all the stars of this system had no relativ movement, when they became part of the cluster. The most likely explanation is that they all developed at the same time, and soon after their birth became entrapped into the cluster. Although it appears that globular clusters indeed contain some of the oldest stars that were produced in the galaxy, their origin relative to the development steps of the universe after the big bang is still unclear.
Globular clusters are located in the so-called halo of our galaxy, i.e. a spherical area in which the disk of our home galaxy is embedded. Around 150 globular clusters are known in the Milky Way.
In many globular clusters, the stars all seem to have been created at the same time. Their state of development depends exclusively on their mass, since this ultimately decides how quickly a star develops. For astronomers, such clusters are therefore interesting as a laboratory for studying star development processes, but also for studying the mutual interactions of stars and their effects on their dynamics.
Unfortunately, there is a relatively low abundance of heavier elements in these star clusters. This means very little chance for the formation of planetary systems, let alone for habitable planets or even extraterrestrial life. As we all know, planets and living matter are all composed essentially on star dust, i.e. the byproducts of supernovae explosions when heavy stars are dying. Why this happens so rarely in star clusters such as NGC 6441 also remains an enigma.
Broken Radius 