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The giant elliptical galaxy in the centre of this image, taken by the NASA/ESA Hubble Space Telescope, is the most massive and brightest member of the galaxy cluster Abell 2261. Spanning a little over one million light-years, the galaxy is about 20 times the diameter of our Milky Way galaxy. The bloated galaxy is a member of an unusual class of galaxies with a diffuse core filled with a fog of starlight. Normally, astronomers would expect to see a concentrated peak of light around a central black hole. The Hubble observations revealed that the galaxy's puffy core, measuring about 10 000 light-years, is the largest yet seen. The observations present a mystery, and studies of this galaxy may provide insight into how black hole behavior may shape the cores of galaxies. Astronomers used Hubble's Advanced Camera for Surveys and Wide Field Camera 3 to measure the amount of starlight across the galaxy, catalogued as 2MASX J17222717+3207571 but more commonly called A2261-BCG (short for Abell 2261 brightest cluster galaxy). Abell 2261 is located three billion light-years away. The observations were taken between March and May 2011. The Abell 2261 cluster is part of a multi-wavelength survey called the Cluster Lensing And Supernova survey with Hubble (CLASH).
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Credit: NASA, ESA, M. Postman (Space Telescope Science Institute, USA), T. Lauer (National Optical Astronomy Observatory, USA), and the CLASH team.
Image enhancement: Jean-Baptiste Faure