Up, Up and Array!

17 January 2012 by Philip James Ma...

Last week, the Very Large Array got a new name: the Karl G. Jansky Very Large Array. So who was this Jansky fellow? And what has the VLA done for us lately, anyway?

Under its old name the VLA was one of the workhorses of radio astronomy, the big telescope that everyone (well, all our American colleagues, at least) would go to for their high sensitivity, high resolution radio images of the sky. Now it has a new name, it still will be! In fact, the reason it has been given a new name is that it’s being expanded, to enable some very exciting science. What do the magnetic fields of galaxies look like? How big are gamma ray bursts? How do radio “jets” work? And how fast did stars form in the very first galaxies? The UK counterpart to the VLA is being upgraded too, to enable the same investigations, but more on that later.

Since October, the National Radio Astronomy Observatory had been accepting suggestions for the name of the expanded VLA, and at the American Astronomical Society’s January meeting, the new name was announced: The Karl G. Jansky Very Large Array. While this may have disappointed the readers of Boing Boing, who thought that “Emily” would have been a good choice, it’s actually very appropriate. Karl Guthe Jansky was a German radio engineer working on transatlantic telephone technology at Bell Labs, New Jersey, in the early 1930’s. Without meaning to, he built the first ever radio telescope: an antenna, mounted on a turntable, that picked up some unexpected signals when he turned it on - one of which, he eventually figured out, was coming from the centre of our Galaxy. Detecting radio waves from outer space was no mean feat in 1932, as his Wikipedia page describes:

“By rotating the antenna on a set of four Ford Model-T tires, the direction of a received signal could be pinpointed. A small shed to the side of the antenna housed an analog pen-and-paper recording system.”

Jansky’s 1933 paper reporting his findings, “Electrical disturbances apparently of extraterrestrial origin”, is an absolute classic: many of the problems he identifies will be all too familiar to modern radio astronomers. For example, he notes:

“the limitations of the apparatus and the errors that might be caused by the ionized layers of the earth’s atmosphere and by attenuation of the waves in passing over the surface of the earth are such that the [position] of the source can be determined only approximately.”

Radio astronomers at Oxford, following Steve Rawlings’ lead, are inventing new ways to correct for this “ionospheric interference” for the low frequency radio telescopes LOFAR and SKA.

Like Karl Jansky’s original radio telescope, each of the Jansky VLA’s enormous antennae are rotatable so we can observe anywhere on the sky (and not just at night!). But the VLA has, not one, but twenty-seven parabolic metal dishes to collect radio waves from outer space. Unlike your own satellite dish, each one is 25 metres in diameter. These enable us to detect and image sources of radio waves most of the way across the Universe. Check out this page for some examples of what astronomers are already doing with the expanded VLA: here in Oxford we’re particularly interested in looking at carbon monoxide to trace star formation in the first galaxies as they formed.

Remember the White Knight from Lewis Carroll’s Alice Through the Looking Glass? Well he would have appreciated the subtle distinction between The Array, The Name of the Array, and What the Name of the Array is Called: it’ll be interesting to see whether radio astronomers actually take up the new name of the VLA, or if they continue to use the old name of this much-loved instrument. We think they’ll switch: scientists are human too, and the opportunity to celebrate a legendary figure is too good to pass up. The Jansky VLA sounds pretty good!

In a companion post to this one, we have a report from one of Oxford Astrophysics’ own legends on progress with e-Merlin, the UK counterpart to the Jansky VLA, and a particularly cunning piece of recycling.

Image courtesy of NRAO/AUI

Categories: marshall | radio astronomy | VLA | rawlings