In keeping with the "astro" theme of the website, I though I would talk about vision and its use in astronomy. The running theme of this site is my lack of vision so naturally its a topic of interest to me anyway.
Centaurus A has always been one of my favorite looking galaxies. I remember seeing this photo in an old astronomy text in the 70’s – it was an image from the 200 inch Mount Palomar observatory. This galaxy is called an active galaxy – meaning that at its core is an active supermassive black hole that puts out a lot of electromagnetic energy, mostly in the non-visual spectrum.
We humans only see a very small chunk of the electromagnetic spectrum – visible light. This is of course ROYGBIV (red, orange, yellow, green, blue, indigo and violet). This is by far not the only sight available. Bats for example use a type of sonar so they "see" by sound.
It’s a highly effective means of getting around – especially in the dark.
Modern military and police technology allow us to see like reptiles do – in the infrared. This technology is called FLIR (forward looking infrared) and basically "sees" heat. The image below shows an F18 fighter jet testing its engine and shows the heat of the engine and the hotter exhaust.
Night vision is a fairly popular bit of technology that uses an infrared intensifier tube, but doesn’t produce an image like FLIR. Its mostly a technology that uses existing light and amplifies it.
Astronomy has some very cool toys that allow us to image in a wide variety of frequencies. It should be noted that while FLIR and night vision is helpful for us to see what we normally do not, these are not useful for astronomy use.
In the constellation Centaurus is the radio source Centaurus A. It’s an active galaxy that is more than meets the eye. Known as NGC 5128, this object was discovered in 1826 at Parramatta Observatory in Australia by James Dunlop. It was ignored for about 100 years as it was thought to be a nebula residing in our own galaxy. It wasn’t until 1949 that it was realized this was another galaxy. Radio observations at that time proved it was another galaxy, and one of the first radio galaxies ever discovered.
The visible image of this galaxy is striking without revealing what is unseen. The dust band with its elliptical shape is actually the result of a galaxy merger between a small spiral galaxy and an elliptical galaxy.
All of the excess debris from two galaxies provides the "food" for the supermassive black hole. In 1969, x-ray emissions were detected by sounding rockets and a 1971 view using the UHURU satellite confirmed the x-ray source. This was the first indication of the black hole.
An interesting event occurred in May of 1986, a supernova in Centaurus A – supernova 1986G. In the image above, it’s the green star on the lower left part of the dust lane.
Radio telescopes are great for mapping out the extent of emission from the black hole. The Very Long Baseline Interferometer in Australia made the most accurate mapping of this emission.
The radio image of this galaxy is radically different from the optical image. The Hubble Space Telescope provided some breathtaking views of the galaxy in 1997. This image mosaic shows the core of the galaxy, a pretty close up view given the narrow field of view of the telescope.
Currently astronomers have what I like to call the dynamic trio of space telescopes: The Hubble Space Telescope, the Chandra x-ray Telescope and the Spitzer Infrared Space Telescope. Couple this with a radio telescope and we have four different views of Centaurus A. The optical views are obvious. The Chandra provides high energy x-ray views which indicate extremely hot energy sources. For example, material being pulled in by the supermassive black hole is compressed so much that temperatures reach extremely high levels. These produce x-rays. The Spitzer space telescope is sensitive to the infrared. A large part of our Universe puts out energy in this wavelength and this telescopes proves excellent for seeing though dusty regions – like seeing through the dust band of Centaurus A.
Put it all together and we get a complete picture of just how active and vast Centaurus A truly is. It’s a far cry from the optical picture alone. The bottom line is there is so much more to our Universe than meets our eye – even if I cannot see it.