The fact the radio waves could originate from space was discovered accidently in 1932 by Karl Jansky whilst he was working as an engineer for Bell in New Jersey. At that time transatlantic telephone calls were made using radio waves, which suffered badly from noise, his investigation of this used an array of metal pipes to serve as an antenna. The results showed that when you discounted the noise due to thunderstorms, the faint static left appeared to originate from the central regions of the milky way.
Astronomers took very little notice of this work, and Jansky couldn't investigate further as Bell labs wouldn't fund his plan to make a huge metal bowl to focus these radio waves. However an amateur astronomer and ham radio operator, Grote Reber, read of Jansky's work, designed and built himself a radio telescope! This 9 meter dish was able to make a crude map of the radio sky, showing the centre of our galaxy, Cygnus A and Cassipeia A being the brightest regions. Although realisation and proof would have to wait about 40 years, he was seeing evidence of super-massive black holes and quasars.
To really see exactly what objects these powerful radio waves were originating from required much better resolution, in fact about 100 times better, or to put it another way a radio dish about a kilometer in size!
This increase in resolution was achieved in 1949 by using the principle of interferometry. This uses two, or more radio telescopes spread widely apart, you can imagine these telescopes as being separate panels of a much larger telescope. You can, using a computer combine the signals, and get a much sharper picture than by using an individual dish. This is at the cost of sensitivity however, if the combined area of your telescopes is only a few percent of the large one you are trying to mimic, you collect less energy, and so your instrument is less sensitive.
These days a great many dishes are combined together to give fantastic resolution, imaging fine detail, billions of light years away. See VLA and the Southern Africa Large Telescope.
Primary source:- Black Holes and Timewarps by Kip S. Thorne. |
