Photograph of NGC 7331 and the "Deer Lick" group with the new supernova SN2025rbs
The image was taken on 08/01/2025 at the S. A. Kolobov Observatory using an ASTROSIB RC500 telescope on an ASTROSIB AVM-700 mount with an SBIG Aluma AC4040-Ultimate (C2) astrocamera. LRGB filters were used, with a total exposure time of 64 minutes.
NGC 7331 and the «Deer Lick» group with supernova SN2025rbs
NGC 7331 is a bright spiral galaxy located approximately 40 million light-years away from us in the constellation Pegasus. It was discovered by William Herschel in 1784 and is often referred to as the «Milky Way's twin» due to its similar size and structure. The galaxy is tilted towards us by about 75°, making its spiral arms and dark dust lanes clearly visible. At its center lies a massive core with a black hole.
Near NGC 7331 in the sky, a group of four faint galaxies is visible — NGC 7335, 7336, 7337, and 7340. They are known as the «Deer Lick Group». Despite their apparent proximity in images, these galaxies are actually much farther away (290–350 million light-years), while NGC 7331 itself lies at a distance of about 40 million light-years. This is merely a projection effect, but it creates a striking visual combination — a large foreground galaxy with tiny «satellites» in the background.
Supernova SN2025rbs
In July 2025, a new supernova — SN2025rbs — flared up in NGC 7331. It was first detected by the GOTO project on July 14th. Based on its spectral characteristics, it was classified as a Type Ia supernova — the explosion of a white dwarf in a binary system when its mass reaches the Chandrasekhar limit (~1.4 solar masses), leading to a catastrophic thermonuclear reaction.
SN2025rbs appeared very close to the galaxy's bright core, complicating observations. At discovery, its brightness was around magnitude 17, but at its peak it rose to magnitude 14, making it accessible to amateur astronomers with medium-sized telescopes. Even by the end of August, its brightness remained around magnitude 14.4 and it was noticeably fading slowly.
This outburst became the fourth recorded supernova in NGC 7331. Previous events were observed here in 1959, 2013, and 2014. SN2014C is especially notable, as it unusually changed its type during its evolution. SN2025rbs turned out to be a «classic» Type Ia representative, but still attracted the attention of astronomers.
Summary
NGC 7331 surrounded by the «Deer Lick Group» is an impressive sight on its own, and the appearance of SN2025rbs made it even more fascinating. A rare opportunity to see a fresh supernova against the backdrop of a famous deep-sky object.
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