The 66 dishes of ALMA – the Atacama Large Millimeter/submillimeter Array – are being equipped with new receivers. They will improve the ability of ALMA to search for water in the Universe.
On Earth, water is very important for life. Out there in the Universe, there’s also a lot of water. Some of the water is in the form of oceans or ice caps on alien planets. That ‘planetary water’ is hard to detect. But there’s also water in the space between the stars. Not in the form of droplets, but just individual water molecules.
When they change their way of rotation, water molecules emit a tiny amount of millimeter radiation. This ‘water emission’ has a wavelength of 1.64 millimeters. It’s a form of ‘light’ that our eyes cannot see. But ALMA can, thanks to sensitive receivers.
The new receivers that are now being installed at ALMA are called Band 5 receivers. They are sensitive to millimeter radiation with wavelengths between 1.4 and 1.8 millimeters. So they’re very good at detecting the faint signal emitted by water molecules in space. The new receivers were designed and built by scientists and engineers in Sweden and the Netherlands.
The Band 5 receiver technology has been tested by looking at a pair of colliding galaxies, and at a very old star. In both cases, water molecules were detected. Right now, all 66 ALMA antennas are being equipped with a Band 5 receiver. That job should be completed by the end of 2017.