Globular Clusters
Read More
M68, Globular Cluster in Hydra
21 May, 2015.
Plane Wave 12.5" CDK, FLI Proline16803, AP900GTO
Exposure was 1.3 hours through Astronomik RGB filters.
Field of View: 36' x 36'
Processed in PixInsight.
M68 is a medium sized globular cluster located in eastern Hydra. It is easily visible with 7x50 or 10x50 binoculars and appears obviously non-stellar. The age of the cluster is estimated at around 11.2 billion years, so that it began forming just 2.5 billion years after the Big Bang.
NGC2802, a Globular Cluster in Carina
19 March, 2015.
Plane Wave 12.5" CDK, FLI Proline16803, AP900GTO
Exposure was 1.8 hours through Astronomik RGB filters.
Field of View: 22' x 22'
Processed in PixInsight.
It had been thought that NGC 2808, like typical globular clusters, contains only one generation of stars formed simultaneously from the same material. In 2007, a team of astronomers led by Giampaolo Piotto of the University of Padua in Italy investigated Hubble Space Telescope images of NGC 2808 taken in 2005 and 2006 with Hubble's Advanced Camera for Surveys. Unexpectedly, they found that this cluster is composed of three generations of stars, all born within 200 million years of the formation of the cluster.
Astronomers have argued that globular clusters can produce only one generation of stars, because the radiation from first generation stars would drive the residual gas not consumed in the first star generation phase out of the cluster. However, the great mass of a cluster such as NGC 2808 may suffice to gravitationally counteract the loss of gaseous matter. Thus, a second and a third generation of stars may form.
An alternative explanation for the three star generations of NGC 2808 is that it may actually be the remnant of a dwarf galaxy that collided with the Milky Way.
Messier 22 in Sagittarius
This is an unguided image of M22, one of the nearer globular clusters to Earth at a distance of about 10,600 light-years away. Its angular size of 32' translates to a spatial diameter of about 100 light years.
M22 is very unusual in that it is one of only four globular clusters that are known to contain a planetary nebula, the others being M15, NGC 6441 and Palomar 6. It was discovered using the IRAS satellite by Fred Gillett et al in 1986 as a pointlike source and subsequently identified as a planetary nebula in 1989.
Messier 55
13 September, 2015.
Plane Wave 12.5" CDK, FLI Proline16803, AP900GTO
Exposure was 1.2 hours through Astronomik RGB filters.
Field of View: 49' x 49'
Processed in PixInsight.
Messier 55 , a globular cluster in Sagittarius, was discovered by Nicolas Louis de Lacaille in June 16, 1752 while observing from South Africa. Starting in 1754, Charles Messier made several attempts to find this object from Paris, France, but the low declination meant it never rose sufficiently far above the horizon to allow for easy observation. He finally observed and catalogued it in 1778.
M55 is 17,600 light-years away. It has a mass of about 269,000 Suns. As with other Milky Way globular clusters, it has a low abundance of elements other than hydrogen and helium compared to the Sun. The proportion of these elements is about 1.1% compared to that of the Sun.