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Centaurus A
Had Messier also observed the southern hemisphere he would surely have seen NGC 5128. Now NGC 5128 is strange galaxy, at first sight it is an elliptical galaxy but on further observation you can see large belt of dust through its centre. Now as ellipitical galaxies do no have any dust (almost by definition) something strange must be going on, and so people postulated that perhaps a spiral galaxy has collided with NGC 5128 leaving behind lots of dust. Now this remained a theory until the advent of multi-wavelength astronomy where we can now take images of celestial objects at wavelengths from radio all the way to gamma rays. This revolution began with the advent of radio astronomy following the technical developments of WW2 in this field. An american engineer called Grote Reber constructed the first radio telescope, and in the style of Messier surveyed the sky looking for radio sources. He found three, one in the constellation of Centaurus, one in the constellation of Sagitarrius, and one in the constellation of Cygnus, and so named them Centaurus A, Sagitarius A, and Cygnus A respectively. Now as radio astronomy improved the positions of these radio sources were pin-pointed, Sagitarius A turned out to be the heart of our galaxy, Cygnus A was seen to co-incide with two galaxies which were obviously in the process of merging, and Centaurus A was located precisely at the co-ordinates of NGC 5128. Well this gave further evidence to the merger theory, as Cygnus A was a merging galaxy, why not Centaurus A. Further improvements to radio astronomy produced the image shown on the right, where we can see that Centaurus A is in fact made up of twin jets dispelling gas into space (a topic which I will continue later).