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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.
                  NASA Web Privacy, Accessibility, Notices;
                      A service of: ASD at NASA / GSFC,
                           NASA Science Activation
                             & Michigan Tech. U.

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