The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical interferometer of 66 radio telescopes located in the Atacama Desert of northern Chile. It observes electromagnetic radiation at millimeter and submillimeter wavelengths, providing unprecedented insights into star birth during the early universe and detailed imaging of local star and planet formation.

Location and Design

ALMA is situated on the Chajnantor plateau at an elevation of 5,000 meters (16,000 feet) above sea level. This location was chosen for its high elevation and low humidity, which are crucial for reducing noise and decreasing signal attenuation due to Earth’s atmosphere.

The array consists of:

• 50 12-meter antennas in the main array
• 12 7-meter antennas in the Atacama Compact Array (ACA)
• 4 12-meter antennas in the Total Power Array

These antennas can be arranged in different configurations, with a maximum separation of up to 16 kilometers, allowing ALMA to achieve varying levels of resolution and sensitivity.

International Collaboration

ALMA is an international partnership involving:

• Europe (European Southern Observatory)
• North America (U.S. National Science Foundation, National Research Council of Canada)
• East Asia (National Institutes of Natural Sciences of Japan, Academia Sinica in Taiwan)
• Republic of Chile

With a cost of about US$1.4 billion, ALMA is the most expensive ground-based telescope in operation.

Scientific Capabilities

ALMA operates at wavelengths of 3.6 to 0.32 millimeters (31 to 1000 GHz). It offers significantly higher sensitivity and resolution compared to earlier submillimeter telescopes. Key capabilities include:

• Spatial resolution of 10 milliarcseconds, 10 times better than the Very Large Array (VLA) and 5 times better than the Hubble Space Telescope
• Ability to image sources arcminutes to degrees across at one arcsecond resolution
• Velocity resolution under 50 m/s
• Point source detection sensitivity 20 times better than the Very Large Array

Scientific Discoveries

ALMA has contributed to numerous scientific breakthroughs, including:

• Detailed imaging of protoplanetary disks around young stars
• Studies of distant galaxies in the early universe
• Detection of complex molecules in interstellar space
• Observations of comets and bodies in our solar system
• Participation in the Event Horizon Telescope project, which produced the first direct image of a black hole

Technical Innovations

ALMA incorporates several technological advancements:

• Custom-built transporters to move the massive antennas
• Superconducting receivers cooled to near absolute zero
• Advanced data processing techniques to handle the enormous amount of data produced

Challenges and Solutions

Operating ALMA presents unique challenges:

• High-altitude operations requiring supplemental oxygen for staff
• Extreme weather conditions in the Atacama Desert
• Managing and processing vast amounts of data
• Coordinating international collaboration

Recent Developments

• In March 2020, ALMA was temporarily shut down due to the COVID-19 pandemic.
• On October 29, 2022, ALMA suspended observations due to a cyber attack. Operations resumed 48 days later, on December 16, 2022.

Summary

ALMA continues to be at the forefront of astronomical research, providing unprecedented views of the cold universe and contributing to our understanding of cosmic phenomena from the formation of stars and planets to the evolution of galaxies. Its international collaboration serves as a model for large-scale scientific projects, while its technological innovations push the boundaries of what’s possible in ground-based astronomy.