Wednesday, 24 February 2016

A shiny crystal ball

When the famous British astonomy pioneer Sir William Herschel pointed his telescope at it back in 1790, he was so amazed by what he saw that he had to completely rethink his idea about the many nebulous objects he had thusfar discovered. Until then, he had always held the belief that all nebulae or fuzzy objects consisted of stars that were simply too remote to resolve in a telescope. But here he saw a star that was clearly enveloped by what he called a "luminous atmosphere". And this observation turned out to be correct.

The Crystal Ball, or NGC1514 in scientific terms, is what's called a planetary nebula. This doesn't mean that there's a planet in it or anything, but rather that it looks a bit like a planet. Indeed, most planetary nebulae are small, round and do look a bit like a planet when observed at lower magnifications. In reality however, a planetary nebula is a shell of gas surrounding an old, dying star. The outer atmosphere of the star is expelled into space by powerful stellar winds, exposing its hot inner core which emits strong ultraviolet radiation. This radiation in turn heats up the nebulosity so much that it starts to emit light on its own and thus making it visible to us. A curious thing about this particular nebula is that its central star is extremely bright compared to the nebula itself. Usually the central stars of planetary nebulae are much fainter and sometimes even invisible to amateur telescopes. Recent studies conjecture that the central star in the Crystal Ball nebula is in fact a very close double star, two stars which orbit each other. In this case they're so close to one another that they're impossible to distinguish by any telescope we possess for the moment and that we can only conclude the presence of a companion star through mathematical deductions of our observations. The orbit of the companion is believed to be so close that it revolves around the main star in a period of only 10 days! So don't be fooled by the little star you see a bit to the upper-left of the central star on my sketch because that one's a lot closer to us than the nebula, which is well over 800 lightyears away in the constellation of Taurus.  

Nebulae like these are very important to the universe because they feed it with heavier chemical elements such as carbon, oxygen and nitrogen which were formed inside of their central star before it started to fall apart. We've also already been able to observe similar nebulae in other galaxies, which tell as a lot about the chemical composition of those. Most planetary nebulae are incredibly spectacular objects which reveal a great deal of detail in larger telescopes and at high magnifications, such as the various and complex gas shells. Unfortunately, due to circumstances beyond my control (well... actually it was all my fault because I'd made some "modifications" to my telescope which made it technically impossible to reach high mags) I couldn't push my telescope beyond 206x anymore. But the two main shells were clearly visible, as was their rather irregular shape. The faint nebulosity inside of these shells indicates that the star's still blowing gas into the nebula. Or in other words, we're testimony to its death struggle. That sounds very dramatic and in a certain way it is also a drama. The universe creates and the universe takes away. But one day perhaps a new star may be born from the ruin of this one.


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