Active supermassive black holes are important drivers of galaxy evolution. Because their high-energy radiation bursts and gas outflows provide material and energy for star formation, astronomers have now observed an eruption in one such active galaxy nucleus that caused unusually fast and strong winds: Within just a few hours, the radiation burst produced outflows in which material shot out into space at almost 60,000 kilometers per second. Data from the XMM-Newton and XRISM X-ray telescopes suggest that these extremely fast winds arise from abrupt changes in strong magnetic fields at the black hole. These eruptions are surprisingly similar to coronal mass ejections on the sun, as the researchers report.
At the center of galaxies are supermassive black holes – giants with several million to billions of solar masses. Most of these black holes are inactive, such as Sagittarius A* at the center of our Milky Way. But there are also galaxies in which the central black holes actively devour large amounts of matter. As a result, these active galactic nuclei (AGN) release intense radiation. In addition, however, short-term bursts of radiation and high-energy particles also occur again and again. The latter then race out into space as a strong wind of hot, ionized gases. “With kinetic energies of up to 1046 erg, such ultrafast outflows are promising candidates for AGN feedback – the process through which the central black hole transfers energy to its host galaxy on a large scale, explain Liyi Gu from Leiden University and her colleagues. According to current theory, the winds of the active galactic nuclei are a driving force for the growth and star formation of galaxies.
X-ray view of the eruption of an active galactic nucleus
“Because of their great influence, it is crucial to learn more about how active galactic nuclei generate their fast winds,” says Camille Diez from the European Space Agency’s Astronomy Center in Madrid. “This could help to better understand the evolution of galaxies in the universe.” But so far, astronomers have only managed to catch such an eruption in the act a few times. In most cases, the resolution of the instruments was not sufficient to show details about the energy and speed of the AGN winds. That’s why the astronomers have now used the European XMM-Newton X-ray telescope and a high-resolution spectrometer from the XRISM X-ray telescope to target a particularly active galaxy nucleus. The XRISM telescope has only been in space since autumn 2023 and is operated by the Japanese space agency JAXA together with ESA and NASA. The target of the ten-day observations was the center of the spiral galaxy NGC 3783, in which a black hole of 28 million solar masses actively devours matter and repeatedly undergoes bursts of radiation.
In fact, a radiation burst occurred at the black hole of NGC 3783 during the observation period: “Over the course of ten days, the intensity of the X-rays increased by around 60 percent, both in the hard and softer X-rays,” report the astronomers. During this outbreak there were also repeated shorter flares. The combined data from the two X-ray telescopes and their measuring instruments enabled Gu and her team to track the speed, structure and origin of the particle streams thrown into space. The observations revealed a striking kink in the radiation curve of the waning burst. As the X-rays gradually faded, the active galactic nucleus ejected strong, fast streams of particles. “We have never seen a black hole generate winds so quickly,” says Gu. “For the first time, we observed how a rapid burst of X-ray light from a black hole immediately triggers ultrafast winds.”
Particle winds with a fifth of the speed of light
The winds generated by the eruption at the black hole raced outwards at around 57,000 kilometers per second – almost a fifth of the speed of light. Further analysis also revealed that these fast particle streams came from the innermost region of the rotating disk of matter around the black hole. Apparently there was a sudden, strong disturbance in the local magnetic fields during the fading radiation burst. “The winds around this black hole appear to have emerged when the AGN’s tangled magnetic field suddenly ‘unraveled,'” explains co-author Matteo Guainazzi from ESA. This means that the trigger for the ultrafast winds at the galactic core is similar to that of a solar eruption – only on a much larger scale. The sun’s flares and coronal mass ejections also arise when “tangled” magnetic field lines of the solar magnetic fields abruptly rearrange and thereby release their energy. Typically, the energy is first discharged in a burst of radiation, followed by an outflow of energetic plasma.
The outbreak now being observed at the central black hole of the spiral galaxy NGC 3783 took a similar course: first there was a violent burst of X-rays, then the stream of fast particles shot out into space. “This is exciting because it suggests that the physics of the Sun and such high-energy environments in the cosmos work in surprisingly familiar ways everywhere,” comments astrophysicist Erik Kuulkers from the XMM-Newton telescope team.
Source: Liyi Gu (Leiden University, SRON Space Research Organization Netherlands) et al., Astronomy and Astrophysics, doi: 10.1051/0004-6361/202557189