For the first time in a decade, the black hole at the center of the M87 galaxy has erupted in an enormous gamma-ray flare, a rare and significant event that defied expectations in the latest analysis by astrophysicists.
Several large collaborations, including the Event Horizon Telescope (EHT), as well as the Fermi Gamma Ray Space Telescope, and the MAGIC, VERITAS, HESS, and EAVN telescopes pooled their resources to observe the massive cosmic event, detailed in a new paper published in Astronomy and Astrophysics.
M87 Black Hole
Messier 87 is also known as Virgo A (for its location in the Virgo Cluster of galaxies) and NGC 4486, although its name is most commonly abbreviated as M87. The brightest object in the Virgo cluster and the largest gravitationally bound structure in the universe, scientists from the Event Horizon Telescope (EHT) published the first images from the black hole at its center in April 2019.
Now, scientists report that M87 has released what appears to be the first high-energy gamma-ray flare astronomers have seen in over a decade, based on observations of the galaxy that incorporated the broadest wavelength range ever observed.
The scale of the event at the heart of the distant M87, but also of the scientific work required to record it, were monumental. Speaking with The Debrief, Kazuhiro Hada, a researcher at Nagoya University in Japan, pointed out that the project cannot truly be said to be led by any one organization, instead referring to it as a “coordinated” effort.
“Our motivation of this study is to understand how (and where) a supermassive black hole produces such an extremely energetic radiation,” Hada told The Debrief. “The origin of very-high-energy gamma-ray emission is a longstanding mystery in black hole astrophysics, while such an explosive event is quite rare so it is hard to foresee when and where it occurs.”
“Moreover, the eye sight (or spatial resolution) of gamma-ray telescopes are very poor, so one needs complementary high-resolution observations at other wavelengths,” Hada added. “Gamma-ray observations in concert with the EHT at radio wavelengths offers an excellent opportunity since the EHT can spatially resolve the M87 black hole, so we have a chance to pinpoint where exactly an active event occurs.”
A Rare Glimpse
In this instance, Hada says the cooperative effort led to the detection of a highly energetic event, which occurred while the the EHT was directly monitoring M87’s black hole.
“Although still not conclusive yet, our multi-wavelength, multi-instrument observations presented here suggest that an explosive gamma-ray event was very likely produced at the base of the outflowing jet, which is the immediate vicinity of the black hole,” Hada told The Debrief.
Hada called the observation “a significant step towards a better understanding of energetic activities caused by supermassive black holes.”
The size of the jet erupting from the black hole shocked Hada and his colleagues. At seven orders of magnitude larger than the black hole’s event horizon itself, the difference resembles the size discrepancy between a tiny bacterium and the largest whale in Earth’s oceans.
The energy burst flared for three days, and scientists estimated that the emission region was three light days, or approximately 170 times the distance between Earth and the sun. The enormous energy eclipsed anything recorded during past observations of the black hole region.
Extreme Acceleration in M87
Comparing the data recorded from broadband spectra to existing theoretical models also proved intriguing.
“The flare in 2018 exhibited particularly strong brightening in gamma rays. It is possible that ultra-high-energy particles underwent additional acceleration within the same emission region observed in quiet states, or that new acceleration occurred in a different emission region,” said Tomohisa Kawashima with the Institute for Cosmic Ray Research, who performed a simulation using a supercomputer installed at the National Astronomical Observatory of Japan.
“How and where particles are accelerated in supermassive black hole jets is a longstanding mystery. For the first time, we can combine direct imaging of the near event horizon regions during gamma-ray flares from particle acceleration events and test theories about the flare origins,” added Sera Markoff, a professor at the University of Amsterdam and co-author of the study.
Next Steps
“There are a number of next to-do things. But one exciting future topic would be to make a “movie” of an active flaring black hole and jet, just like a movie of the Sun with solar flares. Our findings here provides an important guideline for the direction of future black hole researches,” Hada told The Debrief.
“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,” added Giacomo Principe, one of the paper coordinators, a researcher at the University of Trieste associated with INAF and INFN.
“These efforts promise to shed light on the disk-jet connection and uncover the origins and mechanisms behind the gamma-ray photon emission,” Principe said.
The paper, “Broadband Multi-Wavelength Properties of M87 During the 2018 EHT Campaign Including a Very High Energy Flaring Episode,” appeared on December 13, 2024, in the Astronomy & Astrophysics.
Ryan Whalen covers science and technology for The Debrief. He holds a BA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.