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Unique Binary Globular Cluster, M53 and NGC5053
See the associated article here:
www.cloudynights.com/articles/cat/articles/unique-binary-...
M53 (NGC 5024) is a well organized globular cluster in Coma Berenices, discovered in 1775 by German astronomer Johann Bode, then independently discovered by Messier in 1777, and described as a "nebula". William Herschel was the first to resolve it into stars using a larger telescope. He documented it as, "...one of the most beautiful objects I remember to have seen in the heavens." With angular diameter of 13 arcmin, and integrated apparent magnitude of 8.3 (V), it is easily observed in small telescopes as an oval nebulosity, but requires larger apertures for resolution. Its brightest stars are listed as magnitude 13.8, and are predominantly population II red giants. Its lowest metallicity stars indicate the cluster started forming around 12.67 billion years ago. From its estimated mass of 826,000 solar, we can approximate its tidal diameter of nearly 1,600 light years, and well over a million member stars. In its central region, the stars are on average only 0.3 light years apart. The cluster lies at a heliocentric distance of 58,000 ly, and is approaching us at 63 km/s. Situated within the Sgr Dwarf stellar stream, about 60,000 ly above the Galactic plane, along with its binary companion NGC 5053, it is one of the more outlying globular clusters. Considering its well preserved structural coherence during a turbulent history, it is not unreasonable to hypothesize the presence of a central black hole population, or a dense subhalo envelope of dark matter.
NGC 5053 is a very peculiar globular cluster in Coma Berenices, first documented by W. Herschel in 1784. Visually, it is very faint, irregularly oval in shape, gradually brighter toward the center. Compared with its spectacular binary companion, M53, it has only modest stellar content, low luminosity of 40,000 solar, a relatively small physical diameter of 160 ly, and a smaller tidal diameter around 580 ly. Because of loose appearance, low stellar density, absence of a concentrated bright nucleus, and low stellar velocity dispersion, the nature of this cluster as a globular has been doubted for a long time. However, the color-magnitude diagram (CMD) and the HR diagram show a population of blue straggler stars, ten RR Lyrae "cluster variables", and a "knee" between the main sequence and the giant branch characteristic of globular clusters. Tidal disruptions, relatively low total mass, and absence of stabilizing black holes or a dark matter envelope might explain the cluster's peculiar morphological features. Its angular size is 10.5 arcmin, integrated apparent magnitude 9.96 (V), and estimated heliocentric distance 53,500 ly, receding at 43 km/sec. Its brightest red giant stars are of apparent magnitude 14, and horizontal-branch stars average around 16.7. While it is accessible to small apertures photographically, substantial telescopes are required for visual observation. The cluster is remarkable for its extremely low average spectroscopic metallicity of -2.45 dex, among the lowest for Galactic globular clusters. However, based on the age of its oldest individual stars, it seems to have started forming several hundred million years after M53, approximately 12.29 billion years ago.
Unique Binary Globular Cluster, M53 and NGC5053
See the associated article here:
www.cloudynights.com/articles/cat/articles/unique-binary-...
M53 (NGC 5024) is a well organized globular cluster in Coma Berenices, discovered in 1775 by German astronomer Johann Bode, then independently discovered by Messier in 1777, and described as a "nebula". William Herschel was the first to resolve it into stars using a larger telescope. He documented it as, "...one of the most beautiful objects I remember to have seen in the heavens." With angular diameter of 13 arcmin, and integrated apparent magnitude of 8.3 (V), it is easily observed in small telescopes as an oval nebulosity, but requires larger apertures for resolution. Its brightest stars are listed as magnitude 13.8, and are predominantly population II red giants. Its lowest metallicity stars indicate the cluster started forming around 12.67 billion years ago. From its estimated mass of 826,000 solar, we can approximate its tidal diameter of nearly 1,600 light years, and well over a million member stars. In its central region, the stars are on average only 0.3 light years apart. The cluster lies at a heliocentric distance of 58,000 ly, and is approaching us at 63 km/s. Situated within the Sgr Dwarf stellar stream, about 60,000 ly above the Galactic plane, along with its binary companion NGC 5053, it is one of the more outlying globular clusters. Considering its well preserved structural coherence during a turbulent history, it is not unreasonable to hypothesize the presence of a central black hole population, or a dense subhalo envelope of dark matter.
NGC 5053 is a very peculiar globular cluster in Coma Berenices, first documented by W. Herschel in 1784. Visually, it is very faint, irregularly oval in shape, gradually brighter toward the center. Compared with its spectacular binary companion, M53, it has only modest stellar content, low luminosity of 40,000 solar, a relatively small physical diameter of 160 ly, and a smaller tidal diameter around 580 ly. Because of loose appearance, low stellar density, absence of a concentrated bright nucleus, and low stellar velocity dispersion, the nature of this cluster as a globular has been doubted for a long time. However, the color-magnitude diagram (CMD) and the HR diagram show a population of blue straggler stars, ten RR Lyrae "cluster variables", and a "knee" between the main sequence and the giant branch characteristic of globular clusters. Tidal disruptions, relatively low total mass, and absence of stabilizing black holes or a dark matter envelope might explain the cluster's peculiar morphological features. Its angular size is 10.5 arcmin, integrated apparent magnitude 9.96 (V), and estimated heliocentric distance 53,500 ly, receding at 43 km/sec. Its brightest red giant stars are of apparent magnitude 14, and horizontal-branch stars average around 16.7. While it is accessible to small apertures photographically, substantial telescopes are required for visual observation. The cluster is remarkable for its extremely low average spectroscopic metallicity of -2.45 dex, among the lowest for Galactic globular clusters. However, based on the age of its oldest individual stars, it seems to have started forming several hundred million years after M53, approximately 12.29 billion years ago.