HCG 61 - The Box - Compact Galaxy Group in Coma Berenices

This image captures HCG 61, a tight, rectangular arrangement of four galaxies in Coma Berenices known as “The Box.” Composed of NGC 4169, NGC 4173, NGC 4174, and NGC 4175, the trio (excluding foreground member NGC 4173) lies roughly 170 million light-years away; the foreground spire of NGC 4173 lies closer at ~43 million light-years. HCG groups are notable laboratories for studying galaxy interactions, dark matter halos, triggering of nuclear activity, and morphological perturbations. HCG 61 derives its nickname from the approximate rectangular layout of its members.

Image Details & Challenges

Captured via Telescope Live’s SPA-2-CCD system using a 70 cm Officina Stellare RC telescope. The dataset comprises only 1 hour 20 minutes of LRGB exposure, a short duration that tested the limits of faint group imaging. The short integration, combined with the limited frame count, introduced severe color blips and elevated noise levels across the RGB channels. Usual stacking pipelines struggled to reject these artifacts effectively. Used Astro Pixel Processor for initial stacking and generating a synthetic luminance channel. BXT was applied to extract the stars—unavoidably pulling in the blips alongside real stellar data. Created a blip mask with PixelMath to isolate the artifact regions. Leveraged MMT (6 layers) to replace the blip-contaminated pixels using only the residual layer, while maintaining linearity. Once stars were reinserted, remaining color blips were manually removed with the Clone Stamp tool in PixInsight.

Despite these challenges, the final image showcases the core members of HCG 61, their varying morphologies, and the subtle interplay of brightness in a compact group context.

Sources:

deepskycorner.ch

wikipedia.org

Data credit: Telescope.Live