M87 Releases a Rare and Powerful Outburts of Gamma-ray Radiation

In April 2019, the Event Horizon Telescope (EHT) collaboration made history when it released the first-ever image of a black hole. The image captured the glow of the accretion disk surrounding the supermassive black hole (SMBH) at the center of the M87 galaxy, located 54 million light-years away. Because of its appearance, the disk that encircles this SMBH beyond its event horizon (composed of gas, dust, and photons) was likened to a “ring of fire.” Since then, the EHT has been actively imaging several other SMBH, including Sagittarius A* at the center of the Milky Way!

In addition, the EHT has revealed additional details about M87, like the first-ever image of a photon ring and a picture that combines the SMBH and its relativistic jet emanating from its center. Most recently, the EHT released the results of its latest observation campaign. These observations revealed a spectacular flare emerging from M87’s powerful relativistic jet. This flare released a tremendous amount of energy in multiple wavelengths, including the first high-energy gamma-ray outburst observed in over a decade.

The EHT is an international collaboration of researchers from thirteen universities and institutes worldwide that combines data from over 25 ground-based and space-based telescopes. The research, which was recently published in the journal Astronomy & Astrophysics, was conducted by the Event Horizon Telescope Collaboration, the Event Horizon Telescope- Multi-wavelength science working group, the Fermi Large Area Telescope Collaboration, the H.E.S.S. Collaboration, the MAGIC Collaboration, the VERITAS Collaboration, and the EAVN Collaboration.

The study presents the data from the second EHT observational campaign conducted in April 2018 that obtained nearly simultaneous spectra of the galaxy with the broadest wavelength coverage ever collected. Giacomo Principe, the paper coordinator, is a researcher at the University of Trieste associated with the Instituto Nazionale di Astrofisica (INAF) and the Institute Nazionale di Fisica Nucleare (INFN). As he explained in a recent EHT press release:

“We were lucky to detect a gamma-ray flare from M87 during this EHT multi-wavelength campaign. This marks the first gamma-ray flaring event observed in this source in over a decade, allowing us to precisely constrain the size of the region responsible for the observed gamma-ray emission. Observations—both recent ones with a more sensitive EHT array and those planned for the coming years—will provide invaluable insights and an extraordinary opportunity to study the physics surrounding M87’s supermassive black hole. These efforts promise to shed light on the disk-jet connection and uncover the origins and mechanisms behind the gamma-ray photon emission.”

The second EHT and multi-wavelength campaign leveraged data from more than two dozen high-profile observational facilities, including NASA’s Fermi Gamma-ray Space Telescope-Large Area Telescope (Fermi-LAT), the Hubble Space Telescope (HST), Nuclear Spectroscopic Telescope Array (NuSTAR), the Chandra X-ray Observatory, and the Neil Gehrels Swift Observatory. This was combined with data from the world’s three largest Imaging Atmospheric Cherenkov Telescope arrays – the High Energy Stereoscopic System (H.E.S.S.), the Major Atmospheric Gamma-Ray Imaging Cherenkov (MAGIC), and the Very Energetic Radiation Imaging Telescope Array System (VERITAS).

During the campaign, the Fermi space telescope gathered data indicating an increase in high-energy gamma rays using its LAT instrument. Chandra and NuSTAR followed by collecting high-quality data in the X-ray band, while the Very Long Baseline Array (VLBA) and the East Asia VLBI Network (EAVN) obtained data in radio frequencies. The flare these observations revealed lasted approximately three days and occupied a region roughly three light-days in size, about 170 times the distance between the Sun and the Earth (~170 AU).

The flare itself was well above the energies typically detected around black holes and showed a significant variation in the position angle of the asymmetry of the black hole’s ‘event horizon’ and its position. As Daryl Haggard, a professor at McGill University and the co-coordinator of the EHT multi-wavelength working group, explained, this suggests a physical relation between these structures on very different scales:

“In the first image obtained during the 2018 observational campaign, we saw that the emission along the ring was not homogeneous, instead it showed asymmetries (i.e., brighter areas). Subsequent observations conducted in 2018 and related to this paper confirmed that finding, highlighting that the asymmetry’s position angle had changed.”

“How and where particles are accelerated in supermassive black hole jets is a long-standing mystery,” added University of Amsterdam professor Sera Markoff, another EHT multi-wavelength working group co-coordinator. “For the first time, we can combine direct imaging of the near event horizon regions during gamma-ray flares caused by particle acceleration events and thus test theories about the flare origins.”

This discovery could create opportunities for future research and lead to breakthroughs in our understanding of the Universe.

Further Reading: EHT, Astronomy & Astrophysics

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