Galaxies, including our Milky Way, host supermassive black holes at their centers, and their masses are millions to billions of times larger than the sun. Some supermassive black holes shoot fast streams of plasma that emit powerful radio signals, called radio jets.
Radio jets were first discovered in the 1970s. But much remains unknown about how they are produced, especially their energy source and plasma charging mechanism.
Recently, the Event Horizon Telescope Collaboration discovered radio images of a nearby black hole at the center of the giant elliptical galaxy M87. The observation supported the theory that the black hole’s spin powers the radio jets, but did little to clarify the plasma charging mechanism.
Now a research team, led by astrophysicists from Tohoku University, has come up with a promising scenario that clarifies the mechanism of plasma loading in radio jets.
Recent studies have claimed that black holes are strongly magnetized because magnetized plasma inside galaxies carries magnetic fields into the black hole. Then, nearby magnetic energy transiently releases its energy via magnetic reconnection, fueling the plasma surrounding the black hole. This magnetic reconnection provides the energy source for solar flares.
Plasmas from solar flares emit ultraviolet and X-rays; while the magnetic reconnection around the black hole can cause gamma ray emission since the energy released per plasma particle is much higher than that of a solar flare.
The current scenario proposes that the emitted gamma rays interact with each other and produce many electron-positron pairs, which are charged in the radio jets.
This explains the large amount of plasma observed in the radio jets, consistent with the observations of M87. Additionally, the scenario notes that radio signal strengths vary from black hole to black hole. For example, the radio jets around Sgr A*, the supermassive black hole in our Milky Way, are too weak and undetectable by current radio facilities.
Also, the scenario predicts short-term X-ray emission when plasma is charged into radio jets. These X-ray signals are missed with current X-ray detectors, but they are observable by planned X-ray detectors.
“In this scenario, future X-ray astronomy will be able to unravel the mechanism of plasma loading in radio jets, a long-standing mystery of black holes,” said Shigeo Kimura, lead author of the study.
Details of Kimura and his team’s research have been published in Letters from the Astrophysical Journal September 29, 2022.
A rotating black hole powers a jet by magnetic flux
Shigeo S. Kimura et al, Magnetic Reconnection in Black Hole Magnetospheres: Lepton Charging in Jets, Superluminal Radio Spots, and Multi-Wavelength Flares, Letters from the Astrophysical Journal (2022). DOI: 10.3847/2041-8213/ac8d5a
Provided by Tohoku University
Quote: Exploring the plasma loading mechanism of radio jets launched from black holes (2022, September 30) retrieved October 1, 2022 from https://phys.org/news/2022-09-exploring-plasma-mechanism-radio -jets.html
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