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'Seeds' of Massive Black Holes Found at the Center of the Milky Way Galaxy

A research team at Keio University, led by Associate Professor Tomoharu Oka, has discovered intermediate-mass black hole (IMBH) candidates at the center of the Milky Way Galaxy. It is about 30,000 light-years from the solar system in the direction of Sagittarius. IMBH candidates are considered to be the "seeds" that form and grow massive black holes.
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How to Build a Middleweight Black Hole

A new model shows how an elusive type of black hole can be formed in the gas surrounding their supermassive counterparts. In research published in the journal Monthly Notices of the Royal Astronomical Society, scientists from the American Museum of Natural History, the City University of New York, the Jet Propulsion Laboratory of the California Institute of Technology, and the Harvard-Smithsonian Centre for Astrophysics propose that intermediate-mass black holes - light-swallowing celestial objects with masses ranging from hundreds to many thousands of times the mass of the Sun - can grow in the gas disks around supermassive black holes in the centres of galaxies. The physical mechanism parallels the model astrophysicists use to describe the growth of giant planets in the gas disks surrounding stars.
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Middleweight black hole
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Scientists find evidence of first 'middleweight' black hole

Explosive outbursts of super-hot gas in a galaxy 300 million light-years away have provided evidence of the first known "middleweight" black hole, according to scientists who observed the plasma jets with a CSIRO radio telescope.
Called HLX-1 ("hyper-luminous X-ray source 1"), the black hole lies in a galaxy called ESO 243-49, about 300 million light-years away.

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Title: No Evidence for Intermediate-Mass Black Holes in Globular Clusters: Strong Constraints from the JVLA
Authors: Jay Strader, Laura Chomiuk, Thomas Maccarone, James Miller-Jones, Anil Seth, Craig Heinke, Gregory Sivakoff

With a goal of searching for accreting intermediate-mass black holes (IMBHs), we report the results of ultra-deep Jansky VLA radio continuum observations of the cores of three Galactic globular clusters: M15, M19, and M22. We reach rms noise levels of 1.5-2.1 uJy/beam at an average frequency of 6 GHz. No sources are observed at the center of any of the clusters. For a conservative set of assumptions about the properties of the accretion, we set 3-sigma upper limits on IMBHs from 360-980 solar masses. These limits are among the most stringent obtained for any globular cluster. They add to a growing body of work that suggests either (a) IMBHs ~> 1000 M_sun are rare in globular clusters, or (b) when present, IMBHs accrete in an extraordinarily inefficient manner.

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Title: HST's hunt for intermediate-mass black holes in star clusters
Authors: Julio Chanamé (1), Justice Bruursema (2), Rupali Chandar (3), Jay Anderson (4), Roeland van der Marel (4), Holland Ford (2) ((1) Carnegie DTM, (2) Johns Hopkins University, (3) University of Toledo, (4) Space Telescope Science Institute)

Establishing or ruling out, either through solid mass measurements or upper limits, the presence of intermediate-mass black holes (IMBHs) at the centers of star clusters would profoundly impact our understanding of problems ranging from the formation and long-term dynamical evolution of stellar systems, to the nature of the seeds and the growth mechanisms of supermassive black holes. While there are sound theoretical arguments both for and against their presence in today's clusters, observational studies have so far not yielded truly conclusive IMBH detections nor upper limits. We argue that the most promising approach to solving this issue is provided by the combination of measurements of the proper motions of stars at the centers of Galactic globular clusters and dynamical models able to take full advantage of this type of data set. We present a program based on HST observations and recently developed tools for dynamical analysis designed to do just that.

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