On Our Way to the Furthest Places. The Large Millimeter Telescope Alfonso Serrano

The Large Millimeter Telescope Alfonso Serrano (http://lmtgtm.org/?lang=en), also known as LMT (or GMT, its Spanish initials), is a radio telescope with a 50-meter diameter primary reflector, designed and optimized to make astronomical observations at millimeter wavelengths, particularly between 0.85 and 4.0 millimeters. It is located at the top of the extinct Sierra Negra or Tliltépetl volcano at an altitude of 4580 meters above mean sea level, within the Pico de Orizaba National Park, on the border between the states of Puebla and Veracruz [Box 1]. It was built through a binational collaboration between Mexico and the United States, and it is operated by the National Institute of Astrophysics, Optics and Electronics (INAOE) and the University of Massachusetts Amherst (UMass Amherst). 

The diameter of the LMT’s primary reflector allows us to obtain images and observations of wide regions of the sky with an angular resolution or sharpness of up to approximately five arcseconds. This angular resolution is currently only surpassed by interferometric arrangements of radio telescopes such as the Atacama Large Millimeter/Sub-Millimeter Array (ALMA), with which it is difficult to cover large areas. Achieving and maintaining this precision in a movable antenna of 50 meters in diameter represents a major challenge. For this reason, the primary reflector of the LMT is made up of a 180 segments distributed in five concentric rings and anchored to the telescope structure by actuators that can modify their positions in real time. This active surface is able to correct and compensate for gravitational and thermal deformations that affect the surface, thus maintaining optimal alignment. The collecting area of the LMT’s primary surface and the accuracy in its alignment, combined with the altitude and the dry conditions at the top of Sierra Negra make it the largest millimeter radio telescope in the world today. 

The LMT and millimeter and submillimeter wavelength observations in general are a window to the coldest regions of the Universe. This is where stars and planetary systems are usually born; they are usually heavily obscured by large concentrations of molecular gas and dust that prevent optical and ultraviolet photons from reaching our telescopes. It is estimated that more than half of the star formation activity has occurred in these dust-obscured regions for at least the last 11.5 billion years (about 80 percent of cosmic history), which is why millimeter observations are crucial to obtaining a complete picture of the history of the Universe. In addition, there are several physical processes that can be detected and studied with observations in the millimeter region of the electromagnetic spectrum such as:

• The cosmic microwave background distortions induced by diffuse gas in galaxy clusters, which allow us to trace the large-scale structure of the Universe and to determine different cosmological parameters;
• The emission from the active nuclei of galaxies that allows us to study the mass accretion and the growth of supermassive black holes
• The emission of dust in the debris discs around newborn stars, as well as the search for traces of complex molecules in planetary atmospheres, among others.

The LMT and its set of scientific instruments can obtain images and spectra in millimeter light, thus contributing to the study of the formation and evolution of the different structures of the Universe, from giant molecular clouds and regions of star and planet formation in the Milky Way, to the physical processes and chemical composition of some of the most distant galaxies, as well as their spatial distribution across the cosmic web [Box 2]. 

TolTEC (http://toltec.astro.umass.edu/), a new large-format camera recently installed at the LMT, sensitive to light polarization and capable of detecting radiation at 1.1, 1.4, and 2.0 millimeters simultaneously (Box 4), will allow astronomers in Mexico and the world to explore large regions of the sky with a higher level of sensitivity and efficiency. Moreover, as described in more detail below, the LMT is part of the Event Horizon Telescope (EHT, https://eventhorizontelescope.org/) array and, given its qualities and location, its participation has been fundamental in exploring and obtaining the first images of the shadow of supermassive black holes at the center of galaxies M87 and the Milky Way. 

During the following decades, the LMT will continue to be an inspiration and a nursery of ideas for new generations dedicated to technology and science, complementing the observations with a new era of telescopes, interferometers, and space observatories, as well as contributing to a better understanding of the Universe where we live. 

---