Color-composite image of FSR 1735. The cluster is the circular regions of stars and enhanced brightness in the center of the image. North is up and East is to the left.
Credit: Henri Boffin, ESO
New telescope images reveal a previously unknown rich cluster of stars in the inner parts of the Milky Way.
This closely-packed star family, consisting of about 100,000 stars and located some 30,000 light-years away, was spotted with the European Southern Observatory's New Technology Telescope (NTT) at La Silla, Chile.
The discovery was part of a large-scale search for globular clusters in the Galactic Plane--a slice of space in which the star-rich disk of our galaxy lies. Globular clusters are gravity-bound groups of stars with spherical symmetry created at roughly the same time and from the same material. Typically, they are shrouded by dense clouds of gas and dust in the Milky Way, so infrared radiation is the only mechanism to locate such features.
After locating about a dozen clusters with the near-infrared Two Micron All Sky Survey (2MASS), astronomers took new images through three different near-infrared filters--producing images that are 10 times deeper and much more precise than the 2MASS images.
"It has been estimated that the region close to the Galactic Center might contain about 10 so-far unknown globular clusters, and we have started a large campaign to unveil and characterize them," said study team member Helmut Meusinger of the Th?ringer Landessternwarte, an observatory in Germany.
Combing through the new images, the astronomers found FSR 1735, most likely a new globular cluster, which previously appeared to be just a cloud of dust and gas.
"The unique images we have obtained reveal that the nebulous appearance of the cluster in previous images is, in fact, due to a large number of faint stars," said study team member Dirk Froebrich of the University of Kent. "The images show a beautiful, rich and circular accumulation of stars."
FSR 1735, with a mass estimated to be 65,000 times that of the Sun, is about seven light-years wide. Such globular clusters, 150 of which are known in our galaxy, are some of the oldest objects in it and witnesses to the earliest events of the Universe.
"We believe today that galaxy collisions, galaxy cannibalism, as well as galaxy mergers, leave their imprint in the globular cluster population of any given galaxy," Froebrich said. "Thus, when investigating globular clusters, we hope to be able to use them as an acid test for our understanding of the formation and evolution of galaxies."
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