G1

G1, also known as Mayall II, orbits the Andromeda galaxy (M31), the nearest major spiral galaxy to our Milky Way. Located 170,000 light-years from Andromeda's nucleus, G1 is the brightest globular cluster in the Local Group of galaxies. At a distance of 2.9 million light years, it shines at 13.7 mag visual magnitude, and is thus visible as tiny patch in large amateur telescopes. The cluster is also known as SKHB 1 (for Sargent W.L.W., Kowal, C.T., Hartwick, F.D.A., Van Den Bergh, S., who named it G1; Sargent et.al. (1977)), and HBK 0-1 (for Huchra, J.P., Brodie, J.P., Kent, S.M.; Huchra et.al. (1991)).

The crisp image is comparable to ground-based telescope views of similar clusters orbiting the Milky Way. The Andromeda cluster, however, is nearly 100 times farther away (and thus 10,000 times fainter).

A glimpse into the cluster's finer details allow astronomers to see its fainter helium-burning stars whose temperatures and brightnesses show that this cluster in Andromeda and the oldest Milky Way clusters have approximately the same age. These clusters probably were formed shortly after the beginning of the universe, providing astronomers with a record of the earliest era of galaxy formation.

During the next two years, astronomers will use Hubble to study about 20 more globular clusters in Andromeda.

The color picture was assembled from separate images taken in visible and near-infrared wavelengths taken in July of 1994.

Credit: Image and parts of text: Michael Rich, Kenneth Mighell, and James D. Neill (Columbia University), and Wendy Freedman (Carnegie Observatories), and NASA. Data and informations: Leos Ondra

Of this image, high resolution (300 dpi) JPEG images are available in color [722k] and black&white [552 k].

NED data for G1

References:

• John P. Huchra, Jean P. Brodie and Stephen M. Kent, 1991. Extragalactic globular clusters. II - The M31 globular cluster system. Astrophysical Journal, Part 1, Vol. 370, pp. 495-504 (April 1, 1991) [ADS: 1991ApJ...370..495H]
• N.U. Mayall and O.J. Eggen, 1953. Four Nebulous Objects in the Outer Parts of the Andromeda Nebula. Publications of the Astronomical Society of the Pacific, Vol. 65, No. 382, pp. 24-29 (02/1953) [ADS: 1953PASP...65...24M]
• W.L.W. Sargent, C.T. Kowal, F.D.A. Hartwick and S. van den Bergh, 1977. Search for globular clusters in M31. I - The disk and the minor axis. Astronomical Journal, Vol. 82, pp. 947-953 (December 1977) [ADS: 1977AJ.....82..947S]

---

More HST images of M31:

• M31 Core Discovery Panel
• A magnification of the double nucleus of M31.

---

Hartmut Frommert
Christine Kronberg
[contact]

Last Modification: July 3, 1999