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.