The supermassive black hole M87* has become famous for the first photo of a black hole. Now astronomers are presenting exciting new observations of this black hole, some 55 million light-years away, and its jet of radiation and relativistic particles. For the first time, they have succeeded in observing the black hole’s ring of light and jet during a gamma-ray burst as part of a multi-wavelength observation campaign. The recordings and measurement data of this event from the high-energy gamma radiation range through X-ray, UV and visible light to the long-wave radio wave range provide valuable new insights into the origin of such radiation bursts in the environment of active black holes and help to develop theoretical models of the driving forces of the high-energy, accelerated ones limit particles.
The galaxy Messier 87, also known as NGC 4486, is located around 55 million light-years away in the Virgo cluster of galaxies and is best known for its active black hole M87*. This supermassive black hole contains around 6.5 billion solar masses, making it far larger and more massive than the central black hole of the Milky Way. In 2019, M87* became world famous when astronomers at the Event Horizon Telescope (EHT) managed for the first time to image the ring of light around the event horizon and the dark shadow of the black hole itself – it was the first photo of a black hole. A little later, using this network of coupled radio telescopes, astronomers also managed to record the huge jet of energetic particles and radiation that emanates from this black hole. Since 1998, gamma-ray telescopes from M87* have also detected several bursts of radiation in this short-wave, high-energy range of radiation. However, it was not possible to determine the exact origin of these eruptions.
Multi-wavelength campaign at the right time
Now astronomers led by project coordinator Giacomo Principe from the University of Trieste are reporting on the first coordinated observation of M87* and a gamma ray burst at this black hole using telescopes from six international observation networks and in wavelengths from the gamma ray range through X-rays, UV and visible light to long-wave radio radiation. The observations initially confirmed the enormous size of the jet: its length exceeds the diameter of the event horizon by ten million times – this corresponds to the difference between the size of a bacterium and the largest known blue whale. Comparison with the first images of M87* and its jet also revealed that its position and the location of its origin in the black hole’s light ring had changed over the course of this year. “The first image from 2017 showed that the ring’s emission was uneven, with brighter areas indicating asymmetries. Subsequent observations in 2018 confirmed these results and showed that the position angle of the asymmetry had shifted,” says co-author Daryl Haggard, a professor at McGill University.
The big peculiarity of the current results, however, is the radiation burst that happened by chance during the observation campaign in April 2018. “We were fortunate to detect such a gamma-ray burst from M87* during the EHT’s multi-wavelength campaign – the first such event in over a decade,” says Principe. The last gamma ray burst from M87* was detected in 2010. The outbreak was manifested by a sudden increase in gamma radiation. The radiation output above 3,690 gigaelectron volts of energy doubled over the course of 36 hours, as the team reports. The entire burst of brightness lasted about three days in the gamma range. The fortunate coincidence with the multiwavelength observation campaign allowed astronomers to image the source of such a flare and the behavior of the jet at the black hole for the first time. “We have thus obtained a complete set of complementary, simultaneous multi-wavelength observations for M87*, which now supports modeling and interpretation as well as providing data for future research,” explain the astronomers. “Together with the EHT images, these datasets provide valuable information for narrowing down the wide range of theoretical scenarios for accretion and jet origins, as well as for the causes of the radiation burst.”
One-zone model does not fit
The evaluations made it possible for the first time to narrow down the area of origin of such a gamma ray burst. As the astronomers determined, the emission area has a size of around 170 astronomical units. From its situation, the team concludes that the previously discussed model of only one acceleration zone cannot apply in the case of M87*. “This complex, broadband outbreak cannot be modeled by a single-zone model,” report Principe and his colleagues. “Instead, there must be an additional second component or even a third to explain this emission.” The observations are not yet sufficient to clearly determine which theoretical model fits. Nevertheless, the astronomers see their results as important progress. “How and where the particles in the jets of supermassive black holes are accelerated has long been a mystery. For the first time, we can now combine direct images from around the event horizon during a gamma-ray burst and thus test theories about the origins of these bursts,” says co-author Sera Markoff from the University of Amsterdam.
According to the team of astronomers, this success is an example of how radio and high-energy observations of these most massive objects in the universe complement each other. “The contribution of cutting-edge technology in radio astronomy, in coordination with various observing facilities on Earth and beyond, highlights here how multifrequency studies of objects like M87 pave the way for advancing future research and potential breakthroughs in understanding the universe says J. Anton Zensus, director at the Max Planck Institute for Radio Astronomy in Bonn and founding chairman of the EHT collaboration.
Source: Giacomo Principe (University of Trieste) et al., Astronomy & Astrophysics, doi: 10.1051/0004-6361/202450497