Gamma-Ray ‘Blazars’ Uncovered in Landmark Study

In a first for science, a landmark collaboration of over ten academic institutions recently reached the milestone of discovering 200 gamma-ray ‘blazars’ and their origins.

The discovery is the culmination of work first started in 2011 by researchers Dr. Francesco Massaro and Dr. Raffaele D’Abrusco. The study was published in the Astrophysical Journal.


A graphical interpretation by NASA of a gamma-ray blazar bursting from the center of an elliptical galaxy. Image credit: NASA/ JPL-Caltech

In 2011 researchers using NASA’s Wide-field Infrared Survey Explorer (WISE) discovered that blazars display infrared emissions with unique properties that set them apart from similar phenomena.

Blazars, one of the largest known classes of gamma-ray sources, are characterized a highly energetic emission that arises from a jet pointing towards the Earth originating from rapidly spinning supermassive black holes in the center of giant elliptical galaxies,” the researchers said in the paper.

“The radiation from these jets is generated by particles accelerated to velocities very close to the speed of light, that emit over the whole electromagnetic spectrum, from radio frequencies up to the highest energies ever detected, comparable to those released by thousands of supernovae exploding simultaneously. This powerful emission makes blazars the masters of the extragalactic gamma-ray sky.”

Scientists devised a way to identify more blazar candidates by searching for their unique infrared signature throughout the universe. However, an issue became apparent to researchers: to conclusively identify the origin of the blazars, they needed to observe them in visible light, something WISE was incapable of doing.

“When we discovered that the infrared emission of Fermi blazars follows a specific pattern, our first idea was to apply our findings to the search of new infrared sources that could be responsible of the emission associated to the unidentified gamma-ray sources,” said Dr. D’Abrusco.

“While our method turned out to be very effective at selecting potential candidates, we could only confirm their nature by obtaining their optical spectra.”

Thus began one of the largest collaborations in astronomy today.

“We collected spectra in observatories located all around the planet,” Dr. D’Abrusco said.

“After five years and tens of observing nights spent working with telescopes in Arizona (Kitt Peak National Observatory and Multiple Mirror Telescope), California (Palomar Observatory), Chile (Southern Astrophysical Research Telescope and Magellan), Canary Islands (Telescopio Nazionale Galileo and William Herschel Telescope) and Mexico (National Astronomical Observatory in Sa Pedro Martir and Guillermo Haro Observatory), we recently reached the milestone of 200 confirmed gamma-ray blazars among completely unknown blazars and sources whose nature was uncertain before our observational campaign.”

Subsequently, researchers seemed to have uncovered some special candidates. A handful of blazars appear to be in transition, showing significant spectral changes over time. More surprisingly, two blazars lack a radio counterpart, which is a rarity among extragalactic phenomena.

“Our observations represent a major improvement of our knowledge on the demographics of the unidentified gamma-ray sources and gamma-ray blazars,” said Dr. Massaro.

“In the near future, the outcome of our long-term project will allow us to put new more stringent constraints on the nature, abundance and behavior of the dark matter that permeates and drives the evolution of the Universe.”

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