August 2025 - Picture of the Month
The Spare Tyre Nebula (IC 5148) in Grus
Rather than star formation, I've decided to bring you an image of star destruction for a change. This is IC 5148 in Grus, one of the fastest expanding planetary nebulae of which we're aware that lies about 4,200 light-years (1.3 kpc is the GAIA distance to the central star) away in the southern constellation of Grus. As is so often the case, there were multiple independent discoveries which have resulted in two designations, IC 5148 and IC 5150, for this object.
The beautiful patterns and the extended halo in this image are the result of expanding and interacting shells of gas. They're ionised by that tiny blue-white dot in the centre, a white dwarf star with an effective temperature of around 130,000K. It's radiation pressure is sufficient to clear the nearby space of gas, thus allowing us to see it despite being only 16th magnitude. The progenitor star, which was the source for all of this material, would've been relatively ordinary at around 1.5 solar masses.
Although this excellent image was taken by one half of the International Gemini Observatory, there are a small number of images of IC 5148 by amateurs on the web. Certainly worth mentioning, and a look, we have one by Steve Crouch in Australia and another taken by Capella Observatory from Namibia back in 2003. Both of these images show quite a lot of detail, but it's evident that this is not an object that gets much interest. That's probably because of its location just below the celestial equator and relatively small size, about 2 arc-minutes in diameter.
Reference
- Planetary nebula IC 5148 and its ionized halo, D. Barría, S. Kimeswenger, W. Kausch, D. S. Goldman, Astronomy & Astrophysics 620 (2018) A84, DOI: 10.1051/0004-6361/201833981 (Accessed 29 July 2025).
James Whinfrey - Website Administrator.
