Radio core/halo galaxies

• It is a giant elliptical galaxy.
• In a long exposure photograph with visible light, it looks pretty normal.
• In a short exposure photograph, there appears to be a jet of material coming out of the core.
  • It is about 6 kly long.
  • The matter in the jet is moving out from the core at high velocity, up to half the speed of light.
• M87 is a strong radio emitter.
  • Radio radiation concentrated at the core.
  • Radio radiation spreads out through a halo that is roughly the same size as the visible galaxy.
  • The core is small, less than a few light years in diameter.
  • The radio energy output is large, comparable to the visible energy output of our Galaxy.

A black hole?

Here is how one artist imagines that a black hole might look from a planet that orbits a star in the outer reaches of the accretion disk. Note the dust that obscures and reddens the hot gas right next to the black hole at the center. Also note the jets of material shooting out of the poles.

• The jet is a good clue, since accretion disks are thought frequently to have jets of material shooting out their poles.
• It would be nice to see the accretion disk.
• Here is a Hubble Space Telescope picture. Note the jets and the swirling gasses in the middle!
• Are the swirling gasses really swirling? The observers used the Doppler shift to find out. The results show a velocity of 550 km/s at a distance of 60 ly from the center.
• Recall how to measure mass:
  
• Given the rotation speed of of 550 km/s for the gas at a distance of 60 ly from the center, the observers deduced a mass for the object at the center. This rotation speed and distance gives 1.3 x 10⁹ M_sun by my calculation. The Hubble Space Telescope people quote 3x10⁹ M_sun. I suppose that the 550 km/s is the velocity along our line of sight, so that the actual speed is bigger, and that the 3x10⁹ M_sun number is based on their estimate of the actual speed.
• A massive black hole with an accretion disk fills the bill quite nicely. Here is what one of the investigators says:

  "A massive black hole is actually the conservative explanation for what we see in M87. If it's not a black hole, it must be something even harder to understand with our present theories of astrophysics," adds fellow investigator Dr. Richard Harms of the Applied Research Corp. in Landover, Maryland.