Supermassive black holes at the galactic center sometimes launch radio jets, fast-moving plasma outflows which emit strong radio signals. However, much about these radio waves remain unclear: how they are produced, especially their energy source and plasma loading mechanism.
The neighboring black hole at the heart of the massive elliptical galaxy M87 has recently been shown in radio images by the Event Horizon Telescope Collaboration. The observation provided evidence in favor of the idea that the black hole’s spin drives the radio jets but did little to clarify the plasma loading mechanism.
A research team led by Tohoku University astrophysicists has proposed a promising scenario that clarifies the plasma loading mechanism into radio jets.
According to recent findings, black holes are incredibly magnetized because magnetic fields are carried into them by galaxies’ magnetized plasma. The plasma surrounding the black hole is then given energy when nearby magnetic energy briefly loses its energy due to magnetic reconnection.
Solar flares get their energy from this magnetic reconnection. The plasma in the solar flares releases ultraviolet and X-rays. In contrast, the magnetic reconnection around the black hole can cause gamma-ray emission since the released energy per plasma particle is much higher than that for a solar flare.
According to the current scenario, the radiated gamma rays interact with one another and generate many electron-positron pairs, which are then loaded into the radio jets.
According to the scenario proposed by scientists, the radiated gamma rays interact with one another and generate many electron-positron pairs, which are then loaded into the radio jets.
This explains the significant plasma concentration in radio jets, which is consistent with M87 data. The scenario also states that different black holes have different radio signal intensities. Sgr A*, the supermassive black hole in our Milky Way, for instance, has radio jets around it, but they are too faint and undetectable by the current radio equipment.
Also, the scenario predicts short-term X-ray emission when plasma is loaded into radio jets. These X-ray signals are missed with current X-ray detectors but are observable by planned X-ray detectors.
Shigeo Kimura, a lead author of the study, said, “Under this scenario, future X-ray astronomy will be able to unravel the plasma loading mechanism into radio jets, a long-standing mystery of black holes.”