Supermassive black holes

Welcome to my black hole page! If you are looking for a way to grow a supermassive black hole, here's one: Scott Kenyon, Margaret Geller, Warren Brown, and I found that a "small" massive seed black hole in the center of a galaxy can become supermassive (millions to billions of solar masses) if it can disrupt stellar binaries, pairs of stars bound together by their mutual gravitational attraction. If a binary strays close, one member will get captured on a tight orbit around the black hole, and will eventually get swallowed up. The other is flung out, slingshot style, as a "hypervelocity" star. This idea is that it is testable; we can compare observations hypervelocity stars, as well as the stars captured around the black hole; here is our e-print.

Supermassive black holes and the relativistic gas disks around them

The images below represent an accretion disk around a black hole as it would appear to a distant observer. A relativistic ray-tracer calculated the photon trajectories; the images may appear distorted as a result of the gravitational lensing in the strongly curved spacetime.

In this first set of images, we are looking at the supermassive black hole in the center of our own Milky Way Galaxy. The glowing colors show how radio waves from hot glowing gas flowing around the black hole might appear if they were mapped over a small patch of the sky. The black hole lies within the dark spot in the center of each image. No light comes from close to the black hole because its gravitational influence is very strong.

In these images above, the red and blue light distinguish radio waves which are lined up in different directions (think of a long radio antenna pointed vertically versus horizonally). The left most column of images shows how the radio maps might look from near the Galaxy's center, while the other columns show how the map might look from Earth, with our vision blurred by gas in interstellar space that acts like fog.

In the following pictures, color indicates the frequency shift of the observed light across the face of a disk of glowing gas, assuming that the gas is so dense that it is opaque as it orbits around the black hole. Red represents light that is lower in frequency and longer in wavelegth than the light depected in blue; the trend in between is depicted as in the colors of a rainbow.

These images have fairly technical captions next to them, but they just describe different scenarios for gas flows; most have smoothly flowing gas, one shows the effect of turbulence; in some cases the central black hole is spinning, in others it is not. It is important to astrophysicists to decide whether the hole is spinning, because that will guide ideas on how black holes form and may reveal how strong gravity works.

Note that the event "horizon" mentioned below describes how close something can get to a black hole without being sucked in once and for all time. A trip from our world across the horizon is a one-way ticket into the black hole, no changes or refunds. The apparent size of the horizon, as inferred by a distant observer looking at material flowing near it, can reveal properties of the black hole, including its spin.

This image is a geometrically thin disk around an extreme Kerr (maximally rotating) black hole, seen at an inclination of 75 degrees. The inner radius of this "Keplerian" (circularly rotating) disk is at 1.24 R_g, where R_g = G * M/c^2 is the gravitational radius of a black hole with mass M. The outer radius is at 6 R_g. The colors correlate with the observed frequency of light from the disk; the white strip divides redshifted and blueshifted regions. Note that the asymmetric appearance of the inner disk edge is the result of the frame-dragging effect (gravitomagnetism) of black hole rotation.

This disk is located around a Schwarzschild (non-rotating) black hole. It extends from near the horizon at 2 R_g to about 12 R_g, and is seen at an inclination angle of 30 degrees. At large radii the disk material is on circular orbits, but at a radius of 6 R_g, these orbits become unstable. Thus at 6 R_g, the disk material begins a "free fall" orbit which spirals toward the hole. The color map here (and in the images below) indicates only relative changes in observed frequency--most of the photons are actually redshifted.

A model turbulent Schwarzschild disk is shown here. Turbulence is required to help disk material lose angular momentum so it can accrete onto the hole. In doing so it may generate the powerful radiation which we observe in quasars and active galaxies. This disk also has finite thickness associated with the size of turbulent cells (patches of similar color) in the outer disk. The freefalling material nside 6 R_g is smooth in texture; there, no turbulence is required for accretion onto the hole.

A geometrically thin, non-turbulent disk around an extreme Kerr black hole. Disk parameters are similar to the preceding two images, except with the inner radius at 1.24 R_g.

Same as above, except with turbulence. Note that the disk is turbulent all the way down to the inner edge, and that the overall flow is approximately circular.

Finally, this image is of a disk around an extreme Kerr black hole with inner and outer radii of 1.24 R_g and 6 R_g respectively. The intensity of the photons is calculated assuming that the disk is emitting in an optically thick line; Using G. Rybicki's adaptation of photon-escape probability formalism, we can understand the dark stripes as directions where photons from inside the disk are scattered out of the line of sight by surface material. In the bright regions, velocity shear shifts the frequency of the surface material enough so that it cannot reduce the flux by line scattering.

These images were generated with a parallel geodesic solver. BCB is grateful for support from NASA Offices of Earth Science, Aeronautics, and Space Science and the Astrophysical Theory Program.

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	This image is a geometrically thin disk around an extreme Kerr (maximally rotating) black hole, seen at an inclination of 75 degrees. The inner radius of this "Keplerian" (circularly rotating) disk is at 1.24 R_g, where R_g = G * M/c^2 is the gravitational radius of a black hole with mass M. The outer radius is at 6 R_g. The colors correlate with the observed frequency of light from the disk; the white strip divides redshifted and blueshifted regions. Note that the asymmetric appearance of the inner disk edge is the result of the frame-dragging effect (gravitomagnetism) of black hole rotation.
	This disk is located around a Schwarzschild (non-rotating) black hole. It extends from near the horizon at 2 R_g to about 12 R_g, and is seen at an inclination angle of 30 degrees. At large radii the disk material is on circular orbits, but at a radius of 6 R_g, these orbits become unstable. Thus at 6 R_g, the disk material begins a "free fall" orbit which spirals toward the hole. The color map here (and in the images below) indicates only relative changes in observed frequency--most of the photons are actually redshifted.
	A model turbulent Schwarzschild disk is shown here. Turbulence is required to help disk material lose angular momentum so it can accrete onto the hole. In doing so it may generate the powerful radiation which we observe in quasars and active galaxies. This disk also has finite thickness associated with the size of turbulent cells (patches of similar color) in the outer disk. The freefalling material nside 6 R_g is smooth in texture; there, no turbulence is required for accretion onto the hole.
	A geometrically thin, non-turbulent disk around an extreme Kerr black hole. Disk parameters are similar to the preceding two images, except with the inner radius at 1.24 R_g.
	Same as above, except with turbulence. Note that the disk is turbulent all the way down to the inner edge, and that the overall flow is approximately circular.
	Finally, this image is of a disk around an extreme Kerr black hole with inner and outer radii of 1.24 R_g and 6 R_g respectively. The intensity of the photons is calculated assuming that the disk is emitting in an optically thick line; Using G. Rybicki's adaptation of photon-escape probability formalism, we can understand the dark stripes as directions where photons from inside the disk are scattered out of the line of sight by surface material. In the bright regions, velocity shear shifts the frequency of the surface material enough so that it cannot reduce the flux by line scattering.