Gas Disk around a Black Hole
A black hole is an extremely massive yet extremely compact object. Nothing, not even light, can escape from the strong gravity of a black hole. When gas is located near the black hole, that gas falls into the black hole, feeding its growth. Many galaxies are thought to host a black hole which has grown to supermassive size. Large amounts of falling gas have been found around these supermassive black holes. Now, can you imagine what happens in such a situation? This movie shows how the gas glows brightly as it falls towards the black hole, based on recent numerical simulations.
In this movie, the red color indicates regions of high-density gas. The stronger the red color, the higher the density. The blue color indicates regions where radiation can efficiently transport energy across long distances. The stronger the blue color, the more efficient the energy transfer. (*See “Details of Visualization”)
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Gas orbits around the black hole in an “accretion disk.” The gas gradually falls into the black hole while rotating round it. As the gas falls toward the black hole, the gravitational energy is converted to thermal energy. The gas temperature exceeds 10 million degrees, and it emits light. The light collides with the gas, and both the light and gas are ejected from the surface of the accretion disk out into space. The gas flow is accelerated by the radiation to close to the speed of light. This fast, collimated, dilute gas flow propagating outward is called a “jet.” |
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A side-view of the accretion disk. It is not possible to see the black hole at the center through the surrounding massive gas. |
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Close to the black hole, the gas rotates at 30% of the speed of light. However, due to the extremely strong gravity near the black hole, the gas cannot continue to orbit and finally falls into the black hole. As a result, the density of gas near the black hole is reduced. |
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In this simulation, the light spreads out while colliding with gas and changing its direction, because there is a large amount of gas surrounding the black hole. As a result, a diffuse structure is observed instead of a ring structure, such as that observed around the black hole in M87. |
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This is a face-on view of a black hole and its accretion. The intense light from the accretion disk near the black hole primarily travels perpendicular to the disk direction, causing it to look very bright when viewed face-on. Since the accretion disk is extremely hot, it shines brightly mainly in X-rays rather than visible light. |
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The light denoted by the blue color in the movie shows spiral motion while moving outward. This is because the light collides with the gas rotating around the black hole, causing it to be dragged along with the gas and spiral outward. |
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Finally, let’s look at the overall structure. The accretion disk shines brightly as a large amount of gas falls into the black hole. Such a huge mass can be fed into a black hole in black hole binaries, where a star and a stellar mass black hole are orbiting each other. Also, a large amount of mass is supplied when stars fall into the supermassive black hole at the center of a galaxy. These cases are observed as very bright objects. |
Details of Numerical Simulation
| Purpose | To understand the mechanism of the radiation from the accretion disk around a 10 solar mass black hole. |
| Calculation Method | General relativity, magnetohydrodynamics, radiation process, numerical simulation. |
| Number of Grids | 264 x 264 x 64 |
| Computer | Cray XC30 "ATERUI" (CfCA, NAOJ) |
| Time Scale | ~ 0.05 seconds |
| Spatial Scale | The black hole radius is 30 km. The length of the jet from end to end is 7300 km. |
| Resercher | Hiroyuki R. Takahashi (Komazawa University), Ken Ohsuga (University of Tsukuba) |
| References | FORMATION OF OVERHEATED REGIONS AND TRUNCATED DISKS AROUND BLACK HOLES: THREE- DIMENSIONAL GENERAL RELATIVISTIC RADIATION-MAGNETOHYDRODYNAMICS SIMULATIONS, Hiroyuki R. Takahashi; Ken Ohsuga; Tomohisa Kawashima; Yuichiro Sekiguchi, The Astrophysical Journal, Volume 826, Issue 1, article id. 23 (2016). |
Details of Visualization
This movie visualizes a fluid simulation in which the space is divided into radial, latitudinal, and longitudinal grids using software developed with the game engine "Unity." To visualize this simulation result, it was necessary to represent the "flow" throughout the grid. Most of the time, streamlines are used to show flows, but this time, we are expressing a more dynamic flow by letting particles flow throughout the grid. Because this video was made as an all-round stereoscopic image, you can view it with a head mounted display (HMD).
One of the structures to watch in this video is the jet. However, the brightness of the jet changes depending on the viewing angle. The jet appears bright when viewed face-on, but is barely visible from the side. Therefore, in this video, we colored the jet based not on the brightness, but on "the ease with which light energy is transmitted" to make the structure of the jet easily visible from any direction. The stronger the blue color, the more efficiently light energy is transmitted across long distances.
Credits
- Simulation: Hiroyuki R. Takahashi, Ken Ohsuga
- Visualization: Hirotaka Nakayama
- Four-Dimensional Digital Universe Project, NAOJ
YouTube for VR
- Non-stereo VR
Web Browsers: You can aim the movie point-of-view in any direction you prefer by dragging the mouse over the YouTube screen.
Smartphones and Tablets: Using the YouTube App (iOS, Android), all directions can be seen by facing your device in the chosen direction. With VR viewers like Google Cardboard, you can enjoy the full effect of stereoscopic vision in all directions.
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Information
- 2023.4 Version 1.0 was released.
720p
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