Submillimetre astronomy

Special tools help us look at space.

These tools see light that our eyes cannot. This light comes from dust and gas.

The dust catches light from stars. This helps us see how stars are born. We can also see far away galaxies. Some tools fly in space to see better. The air on Earth can hide these things. We put tools in dry and cold places. This helps us see the sky clearly.

Astronomers use special tools to study submillimeter waves. These waves are part of light. They sit between far-infrared and microwave light. We use these waves to see gas and dust in space.

This dust is very important. It can soak up half of the light from stars. The dust then gives that light back. This helps us see how stars are born. It also helps us study far away galaxies.

Looking from Earth can be hard. Water in the air blocks these waves. To fix this, we use special sites. We look for places that are dry and cold. Good sites include Hawaii and Chile. Some tools even fly in balloons or planes. Scientists also send tools into space. The Herschel Space Observatory was a big one. It had a very large mirror. It stayed far away from the Earth and the Sun. This helped it see the origins of galaxies clearly.

Submillimeter astronomy is a special way to look at the universe. Scientists study light waves called submillimeter waves. These waves sit between far-infrared light and microwave light. They are very helpful for seeing things that other light cannot show. For example, they help us find gas and dust in space. This dust is very important because it absorbs up to half of all light from stars. The dust then sends that light back out as submillimeter waves.

By watching these waves, we can learn how stars are born from dark clouds.

This way of looking at space works by tracing specific signals. Astronomers look for things called emission lines. These lines come from gases like carbon monoxide and neutral carbon. These signals help us see molecular clouds and dark cloud cores. We can watch how a star begins to form from its very first collapse. We can also see how molecules in these clouds stay cool. These waves also show us protoplanetary discs and dusty galaxies from the early universe.

This helps us understand how galaxies grow and change over time.

People have used many different tools to study these waves. The Soviet BST-1M was the first submillimeter telescope in space. It sat inside the Salyut-6 orbital station. NASA also launched the Submillimeter Wave Astronomy Satellite, or SWAS, in 1998. This satellite looked at giant molecular clouds. Later, in 2009, the European Space Agency launched the Herschel Space Observatory. Herschel had a very large mirror for its time. It traveled far away from the Earth and the Sun to see clearly.

It focused on how galaxies first began.

Finding the right place to look is a big job. Water in our air blocks these waves. Because of this, telescopes must be in very dry and cold places. Good sites include Mauna Kea in Hawaii and the Atacama Plateau in Chile. The Atacama site has the Atacama Large Millimeter Array, also called ALMA. ALMA uses 54 radio telescopes working together. Another site is the South Pole. Some scientists even use high-altitude balloons or planes to get above the water in the air.

These special locations make the view much clearer.

Submillimeter astronomy connects many different parts of science. It helps us study the cosmic microwave background from the early universe. It even helps us learn about black holes. In 2020, the Event Horizon Telescope used these waves to take the first image of a black hole. This work helps us understand how gravity and matter work together. It is like using a special pair of glasses to see things that are normally hidden. These waves turn the dark, dusty parts of space into a map of discovery.

Submillimetre astronomy is a specialized branch of observational astronomy. It focuses on studying the electromagnetic spectrum at submillimetre wavelengths. These specific wavelengths are also known as terahertz radiation. Astronomers place this waveband between far-infrared and microwave bands. The wavelengths typically range from a few hundred micrometres to one millimetre. Scientists sometimes use the term "microns" to describe these measurements. This field is vital because interstellar dust absorbs much of the universe's light. Astronomers estimate that dust absorbs up to half of all radiation from stars and galaxies. This absorbed energy is re-emitted in the far-infrared and submillimetre bands. By observing these waves, we can see parts of the cosmos that are otherwise hidden.

To understand how this works, we must look at how light interacts with matter. Submillimetre observations trace emission from various gases and dust. Astronomers look for specific emission lines, such as CI, CO, and CII. These lines come from elements like neutral carbon and carbon monoxide. These signals allow us to study molecular clouds and dark cloud cores. We can observe the process of star formation from the earliest collapse to stellar birth. This is done by determining chemical abundances in dark clouds. We also study the cooling mechanisms for the molecules within them. These observations reveal protoplanetary discs and dusty starburst galaxies from the early Universe. They also show the environments surrounding active galactic nuclei (AGN).

Observing these waves from Earth is difficult due to the atmosphere. Water vapour in our air creates absorption bands that block submillimetre radiation. This causes noise and attenuation, which limits our view. To fix this, astronomers look for "windows" of clear visibility between these bands. The ideal observing site must be very dry and cool. It also needs stable weather and must be far from cities. Only a few locations on Earth are suitable for this work. Mauna Kea in Hawaii is a very established and accessible site. The Llano de Chajnantor Observatory on the Atacama Plateau in Chile is another key location. Other excellent sites include the South Pole and Hanle in India. Some scientists even use high-altitude balloons or aircraft to get above the water vapour.

Different types of telescopes are used to capture these signals. Some observatories use single large dishes, like the James Clerk Maxwell Telescope on Mauna Kea. Others use interferometry, which combines many telescopes to work as one. The Atacama Large Millimeter Array (ALMA) is a massive project in Chile. It is an interferometer made of 54 radio telescopes. These include 12 telescopes that are 12 metres wide and 42 that are 7 metres wide. The Submillimeter Array (SMA) at Mauna Kea uses eight 6-metre telescopes. In Chile, the Atacama Pathfinder Experiment (APEX) is the largest submillimetre telescope in the southern hemisphere. Looking forward, the CCAT-prime telescope is scheduled to begin its work in 2026.

Space-based telescopes offer a way to avoid atmospheric interference entirely. The first submillimetre telescope in space was the Soviet BST-1M. It was located inside the Salyut-6 orbital station and used a 1.5-metre mirror. NASA later launched the Submillimeter Wave Astronomy Satellite (SWAS) in 1998. SWAS focused on five specific spectral lines: water, isotopic water, isotopic carbon monoxide, molecular oxygen, and neutral carbon. This helped scientists understand cloud cooling and chemical compositions. In 2009, the European Space Agency launched the Herschel Space Observatory. Herschel used a very large mirror to study the origins of galaxies. It traveled to a Lissajous orbit around the second Lagrangian point of the Earth-Sun system. This position, 1.5 million km from Earth, reduced interference from the Sun and Earth.

Submillimetre astronomy has led to many significant scientific discoveries. It helped measure the Sunyaev–Zeldovich effect in galaxy clusters. This proved that a hot intracluster medium exists. The field also helps scientists constrain models of how planets, stars, and galaxies evolve. By studying the cosmic microwave background (CMB), researchers can investigate the early Universe. This includes studying the role of gravitational waves and relativistic neutrinos. Even the study of black holes relies on this technology. In 2020, the Event Horizon Telescope produced the first image of a black hole. It used radio and far-infrared observations, including Very Long Baseline Interferometry (VLBI) at 870μm. This work connects submillimetre waves to the fundamental laws of quantum gravity.