Friday, 1 December 2017

NGC1893 and IC410: surrounded by tadpoles

Just one and a half degrees south-west of IC405, we find NGC1893, a young star cluster that lies embedded in the nebula from whence it originated some four million years ago. Even from its respectable distance of 12,000 light-years it shines with a magnitude of 7.5 and is therefore an easy target for binoculars. 

The nebula itself is quite a different matter. With its petals whirling around a dark centre, it closely resembles the Rosette Nebula, even though it appears much fainter and smaller due to its distance. In reality, this nebula spans over a hundred light-years across, four times the size of the Orion Nebula! From Earth, you need a medium to large telescope in order to see it and special nebula filters help as well. These filters block all light, apart from the very specific frequencies which these kinds of nebulae emit. The result is that the background and the stars significantly darken but the nebula doesn't. Therefore it becomes more visible because you get a lot more contrast. 

With my binoscope I was able to see some very interesting structures around the central void. The reason why the nebulosity disappears at the centre is because it's being blown away by the radiation of the hot, young stars that have just emerged from it. So here you're looking at a star-forming nebula in a somewhat advanced state of its evolution. As more stars are born, radiation and stellar winds increase, expediting the nebula's evaporation into space. 

Another interesting feature about this nebula is that it contains "tadpoles". They're extremely difficult to see with amateur telescopes and also I was only able to see two of the "heads" (scientifically referred to as "Simeis 129" (top) and "Simeis 130" (bottom)). Just left of the cluster's central stars you'll see two little knots in the nebulosity. The "tails", gas plumes that are blown away from these "heads" and eroded by a powerful stellar wind, were unfortunately invisible to me.