Saturday 18 June 2011

The alternative history of Radio Astronomy

I wrote this history for my thesis but apparently it's 'too colloquial' and 'not relevant' - so this is the edited version, which I've made more colloquial and crazy times...(Papers you may want to read, if you are that way inclined are in  curly {} brackets, just go on arXiv astro-ph and you should find them).

Below is a piccy of me standing on one of the radio antenna at the Very Large Array, just cos that's the kind of rock and roll thing I do generally.

Standing on a Very Large Array Antennae

I start this story of radio astronomy with James Clerk Maxwell in 1873. Maxwell had prooven that visible light was not the only type of electromagnetic radiation, and that actually there was a wide spread of wavelengths either side of the optical spectrum. Inspired by these findings Heinrich Hertz set out to both create and detect electromagnetic radiation, in particular the longer wavelength radio waves {Smith74}. Hertz' work on electromagnetic radiation was held in high regard, resulting in the unit of frequency (Hertz, abbreviated to Hz; equal to one wavelength per second) being named after him. In 1887 Hertz succesfully discovered radio waves; but he was a modest man was Mr Hertz, oh yes,  he did not predict any use for this long wavelengths of radiation that our eyes could not detect. Luckily Guiglielmo Marconi was not as short-sighted and set about to use the radio waves to transmit signals across large distances.

 While Marconi was trying to sending signals across the Earth the likes of Thomas Edison and Sir Oliver Lodge started an attempt to detect radio waves from the Sun. As you do! However, no solar radiation was detected since the detectors available at the time were not sensitive enough and the experiments were actually set up to detect the wavelengths of radio emission which are intercepted by our ionosphere. Bit silly, but hindsight is a wonderful thing...

The birth of radio astronomy finally came in 1932 when Karl Jansky detected radio waves from space while carrying out intereference experiments for Bell laboratories. Jansky was able to determine three possible sources of intereference for communication systems: local thunderstorms, distant thunderstorms and a mysterious signal that occured 4 minutes later every day. The fact that the mysterious signal was coming from a certain direction in space which was fixed relative to the stars, but not fixed with respect to the Earth or Sun allowed him to identify its position as the centre of our galaxy, the Milky Way {Jansky33}.  So what is this mysterious-ness at the centre of our galaxy huh?? This achievement led to the unit of flux density (Jansky, abbreviated to Jy) being named after him.

Further developments in radio astronomy were hindered by the Second World War. However, amateur radio astronomer Grote Reber had been inspired by Jansky's work and took on the challenge of building his own steerable parabolic reflector dish, 30 feet in diameter. As you do!

With his device he was able to map the radio sky and show the startling differences between the optical and radio sky for the first time {Smith74}. Reber published his work in 1940 and 1942 and at the end of the war astronomers collected these findings together with the radar research of scientists such as James Hey. Hey and many other scientists had been employed by the military to improve radar and communications. Hey and his colleagues reported on the efficieny of army radar equipment and investigated reports of jamming by enemy transmitters. These reports led to findings that active sun spots emit radio waves in the metre wavelength region and were later followed up by radio observatories in Sydney and Cambridge. Hey also discovered that meteors leave trails of ionisation in the upper atmosphere which reflect radio waves and that a fluctuating signal coming from Cygnus was a result of the terrestrial atmosphere and that the source itself trasmits steady radiation. Later in 1944, van de Hulst calculated the wavelength of the hyper fine hydrogen spin-flip transition and found that it lay at 21cm, which lies in the radio regime. Astronomers were then able to use radio techniques to trace the motion of this hydrogen gas and map the spiral arms of the Milky Way. Our Earth, orbits the sun in the Orion arm of the Milky Way, and our sun is just one of over 400 billion stars in our galaxy......
The Milky Way

The earlier discoveries acted to catalyse the science of radio astronomy and as radio detectors improved there came the discovery of the cosmic microwave background and pulsars.

In 1965 Penzias and Wilson were studying radio emission from the Milky Way and found a source of noise they could not explain. At first they thought it had something to do with birds poohing on their reciever, so they cleaned it but the noise was still there. Then they realised the noise source wasn't even coming from our galaxy.... This background noise eminated from outside our galaxy with a temperature of 2.7K. Then amazingly, this temperature fitted with an earlier theory that radiation from the Big Bang would have a temperature about 3K. Oh My golly gosh!huh?

Also in the late 60's, Anthony Hewish and Jocelyn Bell working at Cambridge were using a dipole array of 128 elements and found a signal of regular radio pulses due to beamed radiation from strongly magnetised neutron stars {Hewish68}, they had discovered pulsars. At first they thought they had discovered Little Green Men (LGM) aka Aliens, but well they hadn't, nope , just some rapidly rotating neutrons stars...Now you may not think this is that awesome, but it is I can assure you, and when I saw Jocelyn Bell walking down a corridor when I was working in Oxford Uni last Easter, I was very star struck, because here in front of me was the discoverer of pulsars, I mean forget Lady GaGa, this is the real deal as far as inspiring women go, I think!! (Controversely she didn't get the Nobel prize for discovering pulsars, her supervisor did..but hmmm i shan't comment on that). By the 1970's several radio interferometers had been built in an effort to improve the resolution of radio imagery, this now means we can see deep into the centre of active galaxies and resolve jets of material which emerge from the supermassive black hole at the centre.

My thesis is basically based on Very Large Array (VLA) data of an active spiral galaxy (looks a bit like our Milky Way but with a bright 'active' centre, maybe some jets from centre) , which is why there is a picture of me standing on it (the VLA that is, not the active galaxy). But also you should be aware that the VLA is an example of one of these early interferometers which has been around since the 60's. It might also interest you to know that "AIPS" which is the program used to reduce radio images (usually by foolish PhD students who probably niaevely chose radio astronomy ) is based in FORTRAN, which is a rather old programming language (from the 60's)...however, please don't let me mislead you because if you love FORTRAN and can code FORTRAN , that by no means suggests you can use AIPS with ease....Banana Banana. 

Although I may sound pessimistic about my own radio astronomy research I would like to make you aware that at the moment radio astronomy is thriving. What I mean is alot of new and exciting interferometers are being built, and with the building of new devices comes the need for researchers to look at all the masses of data they create, i.e. this means alot of jobs have been recently created in radio astronomy, which is good. LOFAR which is currently the worlds largest telescope (never mind radio telescope) is currently expanding, with antenna based all over the world. And in 2012 they might decide where the SKA will be built, this will be an awesomely sensitive radio interferometer, with very good resolution also.. basically the future is radio bright, the future is astronomy.

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