Researchers clarify dynamics of black hole rotational energy

Astrophysicists at MIPT have developed a model for testing a hypothesis about supermassive black holes at the centers of galaxies. The new model enables scientists to predict how much rotational energy a black hole loses when it emits beams of ionized matter known as astrophysical jets. The energy loss is estimated based on measurements of a jet's magnetic field. The paper was published in the journal Frontiers in Astronomy and Space Sciences.

Astrophysicists have observed hundreds of relativistic jets—enormous outflows of matter emitted by active galactic nuclei harboring supermassive black holes. The matter in a jet is accelerated nearly to the speed of light, hence the term "relativistic." Jets are colossal, even by astronomical standards—their length can be up to several percent of the radius of the host galaxy, or about 300,000 times larger than the associated black hole.

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Credit: MIPT

Fig. 1. A supermassive black hole surrounded by an accretion disk, shown in red, emits jets — the vertical beams.

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Credit: MIPT

Fig. 2. Transverse structure of the magnetic field of a jet.

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This video clip compares the effects on emission lines of spinning and non-spinning black holes.

The video first shows the non-spinning black hole. The accretion disk rotates around the black hole. Note that there is a gap between the inner edge of the accretion disk and the black hole itself. The graph at the bottom shows the shape of the emission from the disk.

The video then shows a spinning black hole. Again the accretion disk rotates around the black hole. Note that disk comes closer to the black hole. The graph at the bottom shows the shape of the emission line.

The animation ends with a side-by-side comparison of the non-spinning and the spinning black holes. The emission from the spinning black hole is less intense than from the non-spinning black hole. It is also spread out over a wider energy range. The rotation of the black hole allows for gas in the disk to get closer. This gas is subjected to a stronger gravitational redshift and higher velocities. These two effects spread the the line over a larger energy range.

 

This artist’s impression illustrates how high-speed jets from supermassive black holes would look. These outflows of plasma are the result of the extraction of energy from a supermassive black hole’s rotation as it consumes the disc of swirling material that surrounds it. These jets have very strong emissions at radio wavelengths.