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Journal or Book Title

The Astrophysical Journal Letters


We report the Chandra/ACIS-S detection of more than 20 ultraluminous X-ray sources (ULXs; L0.5-10 keV 3 × 1039 ergs s-1) in the Cartwheel collisional ring galaxy system, of which over a dozen are located in the outer active star-forming ring. A remarkable hyperluminous X-ray source (HLX; L0.5-10 keV 1041 ergs s-1 assuming isotropic radiation), which dominates the X-ray emission from the Cartwheel ring, is located in the same segment of the ring as most ULXs. These powerful H/ULXs appear to be coincident with giant H II region complexes, young star clusters, and radio and mid-infrared hot spots: all strong indicators of recent massive star formation. The X-ray spectra show that H/ULXs have similar properties as those of the most luminous ULXs found in the nearest starbursts and galaxy mergers such as the Antennae galaxies and M82. The close association between the X-ray sources and the starbursting ring strongly suggests that the H/ULXs are intimately associated with the production and rapid evolution of short-lived massive stars. The observations represent the most extreme X-ray luminosities discovered to date associated with star-forming regions—rivaling the X-ray luminosities usually associated with active galactic nuclei.


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