Giant Virtual Telescope to Study Starbirth
Illustration of gravitational lensing (not to scale). The light from the distant quasar is bent by the gravitational field of an intervening spiral galaxy placed fortuituously near the line of sight. The bending produces two artifact images of the quasar, which are observed by the eSMA. The spiral galaxy itself is located at large distances from the sun, corresponding to only 45% of the current age of the universe.
Credit: spiral (M100): INT/Jacobus Kapteyn Telescope/Johan Knapen/Nik Szymanek; star field: INT/Jacobus Kapteyn Telescope/Cornwall Astronomy School Project; montage: S. Bottinelli

A new giant virtual telescope is the most powerful tool scientists have ever had to study the universe in a part of the electromagnetic spectrum called long wavelength submillimeter light.

The Extended Submillimeter Array (eSMA) was created by combining three telescopes in Hawaii using computer software. By routing them together in a process called interferometry, the combined telescopes have the virtual resolution of one huge telescope the size of the distance between them. In this case, the virtual telescope has a diameter of 782 meters, or about half a mile.

The eSMA is made up of the SubMillimeter Array, which contains eight dishes with 6-meter diameters, as well as the 15-meter James Clerk Maxwell Telescope and the 10-meter Caltech Submillimeter Observatory, all on the summit of Mauna Kea on the Big Island of Hawaii. All the dishes are linked via fiber optic cable to form an enormous virtual telescope akin to the sum of its parts.

"It would be impossible to build a telescope this large, so we take several smaller telescopes," said Sandrine Bottinelli of France's Center for the Study of Radiation in Space. "The radiation is collected by each antenna and then combined by computer software. That allows us to simulate a signal that would be equivalent to what we would get with a single large telescope."

For now, eSMA is the most powerful submillimeter observatory on the planet.

Interferometry is commonly used to string together radio telescopes. Making a submillimeter interferometer is a bit trickier because of the weather conditions required for submillimeter astronomy. The water vapor in the Earth's atmosphere blocks submillimeter radiation in most locations.

"It's more difficult to find a site," Bottinelli told "You need a generally dry and stable atmosphere, so it must be high altitude."

Mauna Kea's lofty location at 14,000 ft (4,000 meters) is perfect.

Scanning the universe through submillimeter light allows astronomers to peer deep into the dusty regions in which new stars, planets and even whole galaxies are being born. These clouds of gas and tiny dust particles are completely dark in visible light, because optical wavelength light is absorbed by the gas and dust. But submillimeter waves, which are longer than optical light waves, can penetrate this material.

Recently Bottinelli led one of the first observations made with the newly-built eSMA. She pointed the scope at a bright radio source located behind a foreground spiral galaxy, which is so far away its light left when the universe was only 20 percent of its current age. The foreground galaxy acts like a lens, bending the light from the radio source and focusing it toward Earth. Since the bright object's light traveled through the galaxy on its way here, it revealed clues about the interstellar gas in the spiral, including the presence of atomic carbon there. Atomic carbon is significant because it plays an important role in building more complex organic molecules.

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