The European Southern Observatory (ESO) is constructing the world’s largest optical/near-infrared telescope, the European Extremely Large Telescope (ELT), on top of Cerro Armazones in the Atacama Desert of northern Chile. With its 39-meter main mirror and pioneering five-mirror design, coupled with state-of-the-art adaptive optics technology, the ELT will collect 13 times more light than the largest visible/infrared telescopes today. This will allow astronomers to peer deeper into the Universe than ever before, opening up new frontiers in astronomical research.
Telescope Design and Construction
The ELT’s revolutionary design features five mirrors working together seamlessly to deliver observations with unparalleled clarity. The primary mirror (M1) consists of 798 hexagonal segments, each measuring 1.4 meters across and 5 centimeters thick. The secondary mirror (M2), tertiary mirror (M3), quaternary mirror (M4), and quinary mirror (M5) all have different shapes, sizes, and roles in the telescope’s optical system.
The construction of the ELT began with a first stone ceremony in May 2017. As of July 2023, the telescope has passed the halfway point in its development and construction, with first light planned for 2028. The giant dome housing the telescope will provide protection from the harsh environment of the Atacama Desert.
The ELT’s construction has faced several challenges, including the need for lengthy analyses to finalize the design, detailed prototyping of critical elements, and subsequent testing. The COVID-19 pandemic also triggered significant delays. However, production processes have now fully resumed, and ESO expects the second half of construction and assembly to progress nearly twice as fast as the first half.
Adaptive Optics
One of the most impressive features of the ELT is its adaptive optics system, which will correct for atmospheric distortions and provide exceptionally sharp images. The system includes the M4 mirror, a flexible, adaptive mirror that will adjust its shape a thousand times per second to correct for distortions caused by air turbulence. The M4 mirror consists of six thin petals, all of which have been finalized and are being integrated into their structural unit.
The adaptive optics system also includes six laser sources, which have been produced and delivered to ESO for testing. These lasers will create artificial guide stars in the upper atmosphere, allowing the system to measure atmospheric turbulence and correct for it in real-time.
Instrumentation
The ELT will be equipped with a suite of cutting-edge instruments designed to cover a wide range of scientific possibilities. Four instruments are currently in advanced design and entering their build phases:
- HARMONI: A visible/near-IR integral field spectrograph that will provide the ELT with its core spectroscopic capability. It will be able to take thousands of spectra simultaneously, allowing astronomers to create detailed maps of astronomical objects.
- MICADO: A near-IR adaptive optics-corrected imager and its associated multi-conjugate adaptive optics system, MORFEO. MICADO will be the first instrument to take advantage of the ELT’s full resolution, providing images 16 times sharper than the Hubble Space Telescope.
- METIS: A mid-IR imager and spectrograph that will study the cold Universe, including exoplanets, circumstellar disks, and high-redshift galaxies.
- ANDES: A visible/near-IR high dispersion spectrograph that will provide ultra-precise radial velocity measurements for the detection and characterization of exoplanets.
Additionally, phase B design studies are about to start for MOSAIC, a visible/near-IR multi-object spectrograph. This multitasker instrument will allow astronomers to measure the light from many objects at the same time, enabling quick surveys of a multitude of stars and galaxies.
Science Goals
The ELT’s unparalleled capabilities will enable astronomers to tackle some of the most pressing questions in modern astronomy. Key science goals include:
Exoplanets and Protoplanetary Disks
One of the most exciting prospects for the ELT is the discovery and characterization of exoplanets, including Earth-like worlds. The telescope will be capable of detecting planets down to Earth-like masses using the radial velocity technique and directly imaging larger planets, potentially even characterizing their atmospheres.
The ELT will also allow astronomers to study protoplanetary disks around young stars, shedding light on the formation and evolution of planetary systems. By detecting water and organic molecules in these disks, the ELT may bring us one step closer to understanding the prevalence of life in the Universe.
The Early Universe and Cosmic Dawn
The ELT will be a powerful tool for studying the early Universe, including the first galaxies, stars, and black holes. By observing these ancient objects, astronomers hope to understand how the Universe evolved from its initial state to the complex tapestry of galaxies we see today.
The telescope will also investigate the epoch of cosmic reionization, when the first stars and galaxies began to ionize the neutral hydrogen that filled the Universe after the Big Bang. This critical period in cosmic history is still poorly understood, and the ELT’s observations will provide crucial insights into the processes that shaped the early Universe.
Stellar Populations and Galaxy Evolution
The ELT will enable detailed studies of resolved stellar populations in nearby galaxies, allowing astronomers to reconstruct their formation and evolution histories. By examining the age, composition, and distribution of stars within these galaxies, researchers can piece together the complex story of galaxy growth and development over cosmic time.
The telescope will also investigate the role of supermassive black holes in galaxy evolution. These enigmatic objects, found at the hearts of most galaxies, are thought to play a crucial role in regulating star formation and shaping the structure of their host galaxies. The ELT’s observations will help to clarify the relationship between supermassive black holes and their galactic environments.
Cosmology and Dark Matter
The ELT will contribute to our understanding of the Universe’s dark sector, including dark matter and dark energy. By studying the distribution and dynamics of galaxies on large scales, astronomers hope to constrain the properties of dark matter and shed light on its nature.
The telescope will also help to elucidate the nature of dark energy by discovering and identifying distant Type Ia supernovae. These stellar explosions serve as excellent distance indicators and can be used to map out the expansion history of the Universe. Additionally, the ELT will attempt to directly measure the Universe’s expansion rate by observing the tiny time-drift in the redshifts of distant objects – a feat that has never been achieved before.
Fundamental Physics
The ELT will provide a unique opportunity to test the laws of physics in extreme environments. By observing the motion of stars and gas around the supermassive black hole at the center of the Milky Way, astronomers can test the predictions of Einstein’s general theory of relativity in the strong-field regime.
The telescope will also search for possible variations in the fundamental constants of nature, such as the fine-structure constant and the proton-to-electron mass ratio, over cosmic time. Any unambiguous detection of such variations would have profound implications for our understanding of the laws of physics and the nature of the Universe.
Summary
The European Extremely Large Telescope represents a major milestone in the history of astronomy and a testament to the power of international collaboration in scientific research. With its unprecedented light-gathering power, adaptive optics system, and suite of cutting-edge instruments, the ELT will push the boundaries of our knowledge and understanding of the Universe.
From the discovery and characterization of exoplanets to the study of the first galaxies and the nature of dark matter and dark energy, the ELT will tackle some of the most fundamental questions in modern astronomy. As the world’s largest optical/near-infrared telescope, it will undoubtedly lead to groundbreaking discoveries that will shape our perception of the cosmos for generations to come.
The ELT is not only a remarkable scientific endeavor but also a showcase for European industry and technological innovation. The challenges posed by the telescope’s design and construction have driven advances in fields ranging from optics and materials science to control systems and data processing. These innovations will likely find applications far beyond astronomy, demonstrating the far-reaching impact of ambitious scientific projects.
As the ELT progresses towards first light in 2028, astronomers worldwide eagerly anticipate the new era of discovery it will usher in. With its unrivaled capabilities, the telescope promises to answer some of the most profound questions about our place in the Universe and the nature of reality itself. In doing so, it will inspire a new generation of scientists and explorers, driving the continued quest for knowledge and understanding that lies at the heart of the human spirit.
