"What is so very special about this place is that, right here above our heads, there is virtually no water vapor. There is just so little that whatever light is emitted from a heavenly body, galaxy or star, it gets here with no interference" explained Gianni Marconi, an astronomer with the Atacama Large Millimeter-submillimeter Array, better known as ALMA (Spanish for "soul"). "And this is the largest observatory that has ever been built."
This spectacular image of the Antenna Galaxies, distorted colliding spiral galaxies about 70 million light-years away, in the constellation of Corvus, combines ALMA observations, made in two different wavelength ranges during the observatory's early testing phase, with visible-light observations from the NASA/ESA Hubble Space Telescope.
The array's early images reveals a view of the Universe that cannot be seen at all by visible-light and infrared telescopes. Thousands of scientists from around the world have competed to be among the first few researchers to explore some of the darkest, coldest, furthest, and most hidden secrets of the cosmos with this new astronomical tool.
It is an array of 66 linked antennas ranging in size from seven to 12 meters acting as a single giant telescope, and it detects much longer wavelengths than those of visible light. Its images therefore look quite unlike more familiar pictures of the cosmos.
Most of the early observations used to create the image of the Antennae Galaxies below were made using only twelve antennas working together — far fewer than will be used for the first science observations — and with the antennas much closer together as well. Both of these factors make the new image just a taster of what is to come.
The Antennae Galaxies are a pair of colliding galaxies with dramatically distorted shapes. While visible light shows us the stars in the galaxies, ALMA's view reveals something that cannot be seen in visible light: the clouds of dense cold gas from which new stars form. This is the best submillimetre-wavelength image ever made of the Antennae Galaxies.
Massive concentrations of gas are found not only in the hearts of the two galaxies but also in the chaotic region where they are colliding. Here, the total amount of gas is billions of times the mass of our Sun — a rich reservoir of material for future generations of stars.
One of the projects chosen for ALMA Early Science observations was that of David Wilner from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, USA. Wilner said, "My team hunts for the building blocks of solar systems, and ALMA is uniquely equipped to spot them." His team's target is AU Microscopii, a star 33 light-years away that is only 1% of the age of our Sun.
"We will use ALMA t image the 'birth ring' of planetesimals that we believe orbits this young star. Only with ALMA, however, can we hope to discover clumps in these dusty asteroid belts, which can be the markers of unseen planets."
Any hunt for habitable planets around other stars often begins with a hunt for water in those distant solar systems. Debris discs, the swarms of dust, gas, and rocks around stars, are suspected also to contain craggy ice chunks filled with frozen water, gas, and possibly even organic molecules — the astrochemistry of life.
Simon Casassus, from the University of Chile, and his team will use ALMA to observe the gas and dust disc around HD142527, a young star that is 400 light-years away. "The dusty disc around this star has a very large gap, which may have been carved by the formation of giant planets," said Casassus. "Outside the gap, this disc contains enough gas to make about a dozen Jupiter-sized planets. Inside the gap, a young gaseous giant planet could still be forming, if there is gaseous material available."
Their ALMA observations will measure the mass and physical conditions of gas interior to the gap. "Thus, ALMA gives us a chance to observe planet formation, or its most recent wake," said Casassus.
Further away, 26 000 light-years from us in the centre of our galaxy, sits Sagittarius A**, a supermassive black hole four million times the mass of our Sun. Gas and dust between it and us hide it from our optical telescopes. However, ALMA is tuned to see through the galactic murk and give us tantalising views of Sagittarius A*.
Heino Falcke, an astronomer at Radboud University Nijmegen in the Netherlands, said "ALMA will let us watch flares of light coming from around this supermassive black hole, and make images of the gas clouds caught by its immense pull. This will let us study this monster's messy feeding habits. We think that some of the gas may be escaping its grip, at close to the speed of light."
Like the black outlines in a child's colouring book, cosmic dust and cold gas trace out structures inside galaxies, even if we can't see those galaxies clearly. At the outer fringes of our visible Universe lie the mysterious starburst galaxies, bright islands in an otherwise calm, dark cosmos. ALMA will hunt for cold gas and dust tracers here, as far back as a few hundred million years after the Big Bang, at a time astronomers call "cosmic dawn".
Masami Ouchi of the University of Tokyo in Japan will use ALMA to observe Himiko, a very distant galaxy churning out at least 100 Suns' worth of stars every year and surrounded by a giant, bright nebula. "Other telescopes cannot show us why Himiko is so bright and how it has developed such a huge, hot nebula when the ancient Universe all around it is so calm and dark," said Ouchi.
"ALMA can show us the cold gas deep in Himiko's star-forming nebula, tracing the movements and activities inside, and we will finally see how galaxies started forming at the cosmic dawn."
During its Early Science observations, ALMA will continue its construction phase in the Chilean Andes, high on the remote Chajnantor Plain in the harsh Atacama Desert.
Each climate-armoured antenna is linked via fibre optic cabling. The views from each distant antenna are assembled into one large view by one of the world's fastest special-purpose supercomputers, the ALMA correlator, which can perform 17 quadrillion operations per second (1.7x1016 operations per second).
The 66 ultra-precision millimetre/submillimetre wave radio antennas working together as one telescope and built by ALMA's multinational partners in Europe, North America and East Asia.