A new way to measure the black hole’s mass

A new method to weigh the central engines of active galaxies.


Astrophysicists from the Moscow Institute of Physics and Technology have demonstrated a new way to measure the mass of black hole indirectly.

Many galaxies have very bright nuclei, so bright that the central region can be more luminous than the remaining galaxy light. These nuclei are called active galactic nuclei. The current consensus is that galactic nuclei produce relativistic jets, an astronomical phenomenon where outflows of ionized matter are emitted as an extended beam along the axis of rotation.

Despite poor understanding, scientists believe that a spinning black hole could power an active galaxy. Scientists tested their method on the Messier 87.

In 1781, astronomers discovered an active galaxy named Messier 87, that is closest to Earth. It was primarily discovered as a nebula, but scientists later realized that it was a galaxy. Later in 1918, astronomers for the first time discovered an optical jet from the galaxy.

The structure of the Messier 87 jet has been meticulously studied since its discovery. The bulk of observations enabled scientists to test hypotheses on the structure of active galaxies, including the relation between the jet shape break and the black hole’s gravitational influence.

Jet behavior and the existence of the supermassive black hole are two sides of the same coin: The former can be clarified in terms of the latter while theoretical models of black holes are tested via jet observations.

Astrophysicists exploited the fact that the jet boundary is made up of segments of two distinct curves and used the distance between the core and the break of the jet, together with the jet’s width, to indirectly measure the black hole mass and spin. For that reason, scientists developed a method that combines a theoretical model, computer calculations, and telescope observations.

Elena Nokhrina, the lead author of the paper, said, “The new independent method for estimation of black hole mass and spin is the key result of our work. Even though its accuracy is comparable to that of the existing methods, it has an advantage in that it brings us closer to the end goal. Namely, refining the parameters of the core’ motor’ to deeper understand its nature.”

Scientists are attempting to describe the jet as a flow of magnetized fluid. For this situation, the shape of the jet is determined by the electromagnetic field in it, which thus relies upon different components, for example, the speed and charge of jet particles, the electric current inside the jet, and the rate at which the black hole accretes matter. A complex transaction between these attributes and physical phenomena offers to ascend to the observed break.

There is a theoretical model that predicts the break, so the team could determine which black hole mass results in the model reproducing the observed shape of the jet. This provided a new model for black hole mass estimation, a new measurement method, and a confirmation of the hypotheses underlying the theoretical model.

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