Intro …
Galaxies are among the most fascinating phenomena in the universe and transport us into a world full of beauty and mystery. These enormous, sparkling islands of stars are not only an impressive sight, but also impressive evidence of the immeasurable vastness and complexity of the cosmos. Their dimensions are beyond our imagination: billions of stars, surrounded by clouds of gas and dust, orbit around a common centre, often dominated by a supermassive black hole.
But galaxies are far more than just spectacular objects – they are also the birthplaces of new stars. Under the influence of gravity and physical processes, new suns are formed in their huge gas nebulae, which could possibly harbour life with their planetary systems. The unimaginable dimensions of these star systems emphasise how small and precious our own place in the universe is, while at the same time they amaze us with their sublime beauty.
M81 with its small blue Companion
M 81 is a large spiral galaxy in the constellation Ursa Major (UMa) and is around 12 million light years away from Earth. It has a diameter of around 90,000 light years and is therefore comparable to the size of our Milky Way. Its conspicuous spiral arms and bright core make it a favourite target for astrophotographers. M 81 interacts gravitationally with the neighbouring galaxy M 82 (see my article from May 2024), which influences star formation in both galaxies. It is part of the M 81 group of galaxies, one of the closest groups of galaxies to the Local Group. M 81 was discovered on 31 December 1774 by Johann Elert Bode.
UGC 5336, also known as Holmberg IX, is a dwarf galaxy in the immediate neighbourhood of M 81 and is regarded as a satellite galaxy of M 81. It is considered one of the youngest known galaxies, as a significant portion of its stellar population was formed in the last 200 million years. Due to its low brightness and diffuse structure, Holmberg IX is a challenging object for visual observations and is also less often captured photographically. The galaxy was named after the Swedish astronomer Erik Holmberg, who first described it.
Holmberg IX is an interesting object of study for astronomers investigating the interactions between galaxies and the formation of dwarf galaxies. Its proximity to M81 and recent star formation offer valuable insights into the dynamics of galaxies.
108 mono shots with 5min each (LRGB + H-alpha)
The total exposure time used for the integration was just under 8 hours, with the luminance channel (48 x 300‘) being used in addition to the red, green and blue colour filters (12 x 300’ each). In addition, the star formation regions were to be emphasised using H-alpha filters (24 x 300″).
As far as image processing was concerned, this galaxy was extremely complex, as the RGB, luminance and H-alpha processing each had to be carried out separately. Finally, to display the correct star colours, the stars were combined separately in luminance and RGB.
The processing of colour data (i.e. RGB filters) Finder also takes place at a completely different level, as the details and sharpness come primarily from the luminance range. The essential tools for editing will soon be written down in a complete workflow. The gradient removal of the PixInsight script from SetAstro is very helpful. Automatic DBE. It combines several work steps (processes) for gradient removal and can also be retraced or edited individually using the History Explorer in PixInside .
In terms of post-processing, this means quite specifically that the exposure time roughly matched the processing time… However, I am very satisfied with the result itself, as the expectations regarding the images of both the small companion galaxy UGC 5336 (the blue-appearing, irregular galaxy directly above M 81 in the image) and the reddish-purple star-forming regions within the spirals of M 81 were completely fulfilled. Obtaining this result in just one night with not too good seeing conditions was really surprising in the end.
The Template
I used Johannes Schedler’s image from the Atlas of Galaxies (König, Binnewies, 2019. 2nd ed. p. 66), which was taken with a 400 mm reflector telescope very close by (Wildon, Austria), as a template for my image. The image was obtained from 6 hours of exposure time:
