Reshmi Mukherjee, the Helen Goodhart Altschul professor of physics and astronomy and spokesperson of the VERITAS Collaboration, is part of a team of leading astrophysicists from across the globe that has released the major scientific finding today that the VERITAS array has confirmed the detection of gamma rays from the vicinity of a supermassive black hole. (VERITAS, which stands for Very Energetic Radiation Imaging Telescope Array System, is a ground-based facility located at the Smithsonian Astrophysical Observatory’s Fred Lawrence Whipple Observatory in southern Arizona.) While these detections are relatively common for VERITAS, this black hole is potentially the first known astrophysical source of high-energy cosmic neutrinos, a type of ghostly subatomic particle.

This discovery is a multi-messenger breakthrough, meaning it relied on various instruments and observatories sensitive to different particles (photons and neutrinos in this case) to make the new finding. It began on September 22, 2017, when the IceCube Neutrino Observatory, led by the University of Wisconsin-Madison’s IceCube Neutrino Observatory, (a cubic-kilometer neutrino telescope located at the South Pole) first detected a high-energy neutrino, a ghostly subatomic particle that can travel unhindered for billions of light years from the most extreme environments in the universe to Earth. Very quickly after the detection by IceCube was announced, telescopes around the world, including VERITAS, swung into action to identify the source. These follow-up observations of the rough IceCube neutrino position suggest that the source of the neutrino is a blazar, which is a black hole of mass between 106 and 109 times that of the sun, with powerful outflowing plasma jets that can change dramatically in brightness over time. This blazar, known as TXS 0506+056, is located about 4 billion light years from Earth.  

Given the importance of higher-energy gamma-ray detections in identifying the possible source of the neutrino, VERITAS continued to observe TXS 0506+056 over the following months, through February 2018, confirming the detection of very-high-energy gamma rays from this object. 

These results are published online in Science and The Astrophysical Journal Letters today. “The potential connection between the neutrino event and the blazar would shed new light on the acceleration mechanisms that take place at the core of these galaxies, and provide clues on the century-old question of the origin of cosmic rays—or matter from outside our solar system,” said spokesperson Mukherjee, co-author of the findings published in Science

“These results offer the first evidence for the observation of a source of high-energy neutrinos and cosmic rays and highlights the power of multi-messenger astrophysics,” says Mukherjee. 

“The group at Barnard has been studying the connection between gamma rays and neutrinos over the last few years, searching for gamma rays from the direction of neutrinos observed by IceCube, and has involved undergraduate students analyzing data from space- and ground-based observatories,” said Marcos Santander, who led the study for VERITAS and was a research scientist at Barnard from 2015 to 2017. He is currently assistant professor of physics and astronomy at the University of Alabama. “This result is the product of the work and support that the VERITAS group has received at Barnard.”

Every year, Mukherjee engages Barnard and Columbia students in VERITAS research, and often takes them for observing trips to the VERITAS Observatory at the Fred Lawrence Whipple Observatory. Last year, the telescope system marked its tenth anniversary with a conference celebration co-sponsored by Barnard. At the event, Mukherjee highlighted that the telescope system could detect a source in less than half the time it took to do so a decade ago and as a result, she and the team have detected gamma rays from sources in the Milky Way, as well as from several distant blazars, including one from more than half way across the visible Universe. (Read about this blazar in “The Great Escape.”) The VERITAS Collaboration consists of about 80 scientists from 20 institutions in the United States, Canada, Germany, and Ireland. VERITAS research at Barnard College is supported by the National Science Foundation (NSF).

The news was announced at a press conference hosted by NSF Director France Córdova.

●    To watch the NSF press conference, click here.
●    For more on Mukherjee’s work with VERITAS, click here.
●    To read the published papers, visit: "Multi-messenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A” 
●    To read the VERITAS paper on these results, visit: “VERITAS observations of the BL Lac object TXS 0506+056”