Music. Tea. Justice. (Bitey mad lady with a love of physics, food, and fiction, and a hyper-literate prog rock soundtrack.)
Galaxies don’t normally look like this. NGC 6745 actually shows the results of two galaxies that have been colliding for only hundreds of millions of years.
Just off the above digitally sharpened photograph to the lower right is the smaller galaxy, moving away. The larger galaxy, pictured above, used to be a spiral galaxy but now is damaged and appears peculiar. Gravity has distorted the shapes of the galaxies.
Although it is likely that no stars in the two galaxies directly collided, the gas, dust, and ambient magnetic fields do interact directly. In fact, a knot of gas pulled off the larger galaxy on the lower right has now begun to form stars. NGC 6745 spans about 80 thousand light-years across and is located about 200 million light-years away.
One night, Harvard astronomer Alex Parker was camped out at the telescope for a spot of star-gazing, and found himself facing a long, dry period of waiting for the clouds to clear. To pass the time, he started playing around with various images from the Hubble Space Telescope, and ended up assembling them into a colorful mosaic.
This image was taken by the Advanced Camera for Surveys on board the Hubble Space Telescope. I had to cut it and compress it drastically to get it to fit on the blog, so you very much want to click on it to embiggen it massively and see it in its fully resolved glory. The image is of the insanely beautiful globular cluster M30, an ancient city of a few hundred thousand stars located 28,000 light years away in the constellation of Capricornus. The cluster is ancient, about 13 billion years old, making it as old or even older than the Milky Way itself. The core of the cluster is unusually dense as such things go, which is why it was studied. Where better to find vampires and thrillseekers?
A rich deposit of gas and dust in the NGC 3324 region fuelled a burst of starbirth there several millions of years ago and led to the creation of several hefty and very hot stars that are prominent in the new picture. Stellar winds and intense radiation from these young stars have blown open a hollow in the surrounding gas and dust. This is most in evidence as the wall of material seen to the centre right of this image. The ultraviolet radiation from the hot young stars knocks electrons out of hydrogen atoms, which are then recaptured, leading to a characteristic crimson-coloured glow as the electrons cascade through the energy levels, showing the extent of the local diffuse gas. Other colours come from other elements, with the characteristic glow from doubly ionised oxygen making the central parts appear greenish-yellow. (via Who do you see in this massive silhouette in space?)
The striking features in this image are the big red emission regions Barnards Loop and the Lambda Orionis Nebula (around Orions “head”), both predominantly visible in the light of ionized hydrogen (H-alpha, 656nm). Barnards Loop is a remnant of one or maybe several Supernova explosions. This loop is, as known from radio-astronomy, much more extended than it can be seen here. Just the inner part of the material is ionized by high energetic radiation of the Orion OB1-Association. This are the blue, hot and massive stars of Orions “belt” and the surrounding. A completely different star color is shown by Beteigeuze (Alpha Orionis, left “shoulder”) with its intensive orange. The surface temperature is with 3500 K very low and so the maximum of the radiated energy spectrum is positioned in red.