A duo of astronomers has spotted three new globular clusters in the Milky Way’s bulge, a 10,000-light-year-wide central structure made primarily of old stars, gas and dust.
The globular cluster Camargo 1107. Image credit: D. Camargo & D. Minniti, doi: 10.1093/mnrasl/slz010.
Globular clusters are ancient groups of thousands or even millions of stars, gravitationally bound into a single structure about 100-200 light-years across.
They are among the oldest known objects in the Universe and are relics of the first epochs of galaxy formation.
“As relics of star formation in the early Universe, globular clusters may provide important clues on the Milky Way history,” said Dr. Denilso Camargo from the Federal University of Rio Grande do Sul in Brazil and Dr. Dante Minniti from the Universidad Andres Bello in Chile.
“In the current view, bulges are classified in classical bulges and pseudobulges or disk-like bulges,” they explained.
“Classical bulges are thought to emerge from violent events such as galaxy mergers or sinking of giant gas clumps and host older stellar population within a spherical structure like elliptical galaxies. Flattened disk-like bulges may arise on longer timescales via internal processes such as disk instabilities and secular evolution.”
“Since globular clusters basically witnessed the entire history of our Galaxy, they may allow us to reconstitute the chain of physical processes experienced by the Milky Way from its origin to the present-day.”
“However, the census of globular clusters in the Milky Way is still far from complete, especially for the bulge globular clusters.”
Camargo 1108. Image credit: D. Camargo & D. Minniti, doi: 10.1093/mnrasl/slz010.
The newly-discovered globular clusters, named Camargo 1107, 1108, and 1109, are located at distances between 10,800-14,000 light-years from the Sun and are close to the Galactic mid-plane.
They are very old and extremely poor in what astronomers call ‘metals’ (elements heavier than helium), with ages in the range from about 12 to 13.5 billion years.
“Camargo 1107, 1108, and 1109 may be the remaining of a primordial class of globular clusters that were destroyed mainly by dynamical processes and are the source of the ancient field stars that inhabit the Milky Way bulge and the inner halo,” the astronomers said.
“Previous works suggest that there are a significant fraction of globular clusters which were formed just after the Big Bang, around the epoch of reionization.”
Camargo 1109. Image credit: D. Camargo & D. Minniti, doi: 10.1093/mnrasl/slz010.
“These globular clusters suggest that the Milky Way central region hosts a sub-population of very old and metal-poor globular clusters, which is consistent with being an inner halo component,” they said.
“Alternatively, these clusters may be part of an old classical bulge built up by merging in the early history of the Milky Way.”
The discovery is reported in a paper in the Monthly Notices of the Royal Astronomical Society: Letters.
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D. Camargo & D. Minniti. 2019. Three candidate globular clusters discovered in the Galactic bulge. MNRASL 484 (1): L90-L94; doi: 10.1093/mnrasl/slz010
