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                           Astronomy Picture of the Day   
      
       Discover the cosmos! Each day a different image or photograph of our   
         fascinating universe is featured, along with a brief explanation   
                       written by a professional astronomer.   
      
                                    2025 May 4   
       An artistic illustration of a black hole is shown. The black spot in   
           the center is the black hole, while the accretion disk of gas   
       surrounding it is shown in orange. Stars and the darkness of space is   
       shown near the top in the background. Please see the explanation for   
                            more detailed information.   
      
                       Spin up of a Supermassive Black Hole   
                Illustration Credit: Robert Hurt, NASA/JPL-Caltech   
      
      Explanation: How fast can a black hole spin? If any object made of   
      regular matter spins too fast -- it breaks apart. But a black hole   
      might not be able to break apart -- and its maximum spin rate is really   
      unknown. Theorists usually model rapidly rotating black holes with the   
      Kerr solution to Einstein's General Theory of Relativity, which   
      predicts several amazing and unusual things. Perhaps its most easily   
      testable prediction, though, is that matter entering a maximally   
      rotating black hole should be last seen orbiting at near the speed of   
      light, as seen from far away. This prediction was tested by NASA's   
      NuSTAR and ESA's XMM satellites by observing the supermassive black   
      hole at the center of spiral galaxy NGC 1365. The near light-speed   
      limit was confirmed by measuring the heating and spectral line   
      broadening of nuclear emissions at the inner edge of the surrounding   
      accretion disk. Pictured here is an artist's illustration depicting an   
      accretion disk of normal matter swirling around a black hole, with a   
      jet emanating from the top. Since matter randomly falling into the   
      black hole should not spin up a black hole this much, the NuSTAR and   
      XMM measurements also validate the existence of the surrounding   
      accretion disk.   
      
                  Hole New Worlds: It's Black Hole Week at NASA!   
                         Tomorrow's picture: planet lines   
        __________________________________________________________________   
      
          Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)   
               NASA Official: Amber Straughn Specific rights apply.   
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                         A service of: ASD at NASA / GSFC,   
                              NASA Science Activation   
                                & Michigan Tech. U.   
      
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