© European Southern Observatory
It may not be self-aware (yet) but this computing monster is ready to take over the world. Well, at least a telescope in Chile.

Say hello to the correlator for the Atacama Large Millimeter/Submilimeter Array, or ALMA. The correlator is the computer that runs at the backend of an array of radio telescopes called an interferometer. It, very basically, combines all the signals of the antennas so that it can function as one single telescope.

The correlator was largely constructed in the building right across from where I did a lot of my graduate work at the National Radio Astronomy Observatory in Charlottesville, Virginia. I used to take any excuse, usually a visiting tour group, to gaze at the supercomputing monstrosity, although they were only working on it in sections. The picture above gives you a better sense of its full size.

Though large (134 million processors) and fast (17 quadrillion operations per second), this computer has just one purpose: to suck in all of the data from ALMA's 66 dishes and transform it into data that can then be sent to the astronomers to calibrate and analyze. The correlator gives the interferometer its power to see incredibly fine detail and small structures, such as protoplanetary disks and distant star-forming galaxies.

The correlator came online in December as yet another step towards completing ALMA, a telescope that will give astronomers an unprecedented look at the sky in millimeter wavelengths. First science results have already been coming in from a partial array and correlator, giving scientists a tantalizing glimpse at what the full power of the array will hold.

© European Southern Observatory
To the left is a picture of the back of a tiny section of this giant correlator. With 66 antennas, there are over 2000 combinations of antenna pairs, which leads to thousands and thousands of physical connections that must be made between circuit boards by hand. I think it is fair to say that wires were crossed more than once, and a consistent labeling scheme was necessary.

As impressive as this correlator is, it may be the last of its kind in an era where correlation is also being done by different methods, such as software correlators. The current correlator in use at the Very Long Baseline Array (VLBA) looks like, and actually is, a small cluster of commercially available computer towers. Not so long ago, the VLBA correlator was fed by huge tape machines which I also used to watch whir and spin while taking a break from research in Socorro, New Mexico.

The technology changes while the function basically stays the same. The ALMA correlator will surely seem an archaic thing by the time it gets decommissioned far in the future. However, it has many years of discovery and cutting edge science before that happens.