Mexico on the Frontier of Astronomical Research. Exploring the Most Energetic Objects in the Universe

Gamma-ray astrophysics is a branch of astrophysics that focuses on observing this higher-energy form of electromagnetic radiation emitted by various cosmic sources. These rays have energies over 100 kiloelectronvolts, exceeding the energy of visible light and of X-rays,  providing valuable information about some of the most energetic and extreme processes in the Universe. The physics of gamma rays involves their interaction with matter: gamma photons are absorbed by electrons in atoms, which result in the release of energy and, when at high energies, the creation of particles. These interactions are ruled by the principles of quantum mechanics and special relativity, contributing to our understanding of fundamental physics.

Gamma-ray emissions come from a variety of extreme cosmic environments, such as active galactic nuclei (AGN), supernova remnants, neutron stars, black holes, and gamma-ray bursts (GRBs). At these sites, highly energetic particles accelerated to relativistic velocities interact with the surrounding environment to produce gamma rays. Studying these emissions is crucial to understanding phenomena such as the formation of black holes, the acceleration of particles in magnetic fields, and the processes occurring in supernova remnants. Gamma-ray astronomy also allows us to probe populations of high-energy particles in the cosmos, furthering our understanding of the origins of cosmic rays. 

Detecting gamma rays is a remarkable challenge. Although they can get through the atmosphere and solid matter without interacting directly like other high-energy particles, conventional telescopes do not detect them. However, whenever gamma rays interact with air molecules, mainly oxygen and nitrogen, they produce secondary particles—such as electrons—that travel faster than the speed of light in air. This interaction prompts Cherenkov radiation, a faint blue light that telescopes can detect. Cherenkov radiation also occurs when secondary particles generated by the interaction of gamma rays in water move above the speed of  light in this medium [see box]. This process is used in experiments and detectors like the HAWC observatory [High Altitude Water Cherenkov; see González, p. XX in this issue], which uses water to detect these interactions. 


The detection of Cherenkov radiation depends on ground-based instruments such as airborne Cherenkov telescopes, which measure the light emitted when high-energy particles from gamma-ray interactions impact the atmosphere. Astronomy can infer gamma-ray source’s direction, energy, and nature by analyzing the shape, intensity, and timing of Cherenkov light pulses. These methods have been used effectively by the HESS, MAGIC, and VERITAS observatories to detect gamma rays from various cosmic objects such as pulsars, supernova remnants, and distant AGN. Orbital telescopes such as Fermi also play an essential role in detecting gamma rays, especially at lower energies, by observing the sky from space. 

Some recent studies have begun to provide new approaches to gamma-ray sources. For example, it has been suggested  that supernova remnants may be playing a significant role in the production of high-energy gamma rays as well as in the acceleration of cosmic particles. Such findings have generated significant interest in the acceleration mechanisms in supernova explosions and their ability to create particles at near-light speeds. 

Another interesting case is the study of active Blazar galaxies. These systems have relativistic jets that emit radiation at various wavelengths, including gamma rays. Blazars provide an excellent opportunity to study the physics of matter near supermassive black holes; their gamma-ray emission is used to explore phenomena such as particle acceleration and the propagation of radiation through the galaxy’s atmosphere. 

GRBs also continue to be an area of intense research. They are extremely bright, short-lived episodes of gamma-ray emission  associated with the death of massive stars and the formation of black holes. Their study provides crucial information on high-energy physics under extreme conditions, such as general relativity and stellar merger processes. 

Mexico has made significant contributions to these studies, particularly since its participation in HAWC. Located in the Sierra Negra mountains of Mexico, HAWC detects cosmic rays and high-energy gamma rays and provides key data about the most energetic objects in the universe. In addition, the recent discovery of high-energy gamma rays from LHAASO (Large High Altitude Air Shower Observatory) has risen the enthusiasm of the astronomical community towards new insights on the origins of cosmic rays and other high-energy phenomena. Mexico’s participation in these cutting-edge projects highlights its important role in enhancing our understanding of the Universe and the powerful sources of gamma radiation. 

As we look ahead to the future, the continuous development of advanced telescopes and collaborations will allow us to explore the most energetic phenomena in the Universe at an even greater depth. The study of gamma rays—with the help of facilities such as HAWC and LHAASO—promises to revolutionize our understanding of high-energy astrophysics and the fundamental operation of the Universe. Mexico’s growing presence in these initiatives underscores its contribution to this exciting frontier of scientific exploration.

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