Supernova SN 2025rbs

Astronomy
Written By Willem Jan Drijfhout
 

Supernova SN 2025rbs is only recently discovered and currently one of the brightest supernovae in the night sky.

 

When I published my image of Caldwell 30 (NGC 7331) on Astrobin, a member (Space_Man_Spiff) commented and remarked that a recently discovered supernova was visible in the image. At the time I was not aware of this supernova, but obviously after this comment I did some further research. And indeed, I had accidentally photographed a supernova barely a month after its discovery, and currently one of the brightest supernovae in the night sky.

 

SN 2025rbs

This supernova was first discovered on 14 July 2025, by GOTO-N. This is a site at the Roque de los Muchachos Observatory (ORM) on the island of La Palma, Spain. GOTO stands for Gravitational-Wave Optical Transient Observer and is an array of robotic optical telescopes optimized for the discovery of optical counterparts to gravitational wave events and other multi-messenger signals. The array consists of a network of telescope systems, with each system consisting of eight 0.4m telescopes on a single mounting. Besides the site on La Palma, there is a similar site in Australia, referred to as GOTO-S.

SN 2025rbs is classified as a Type Ia supernova. A Type Ia supernova is a supernova that occurs in binary systems in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf. If the white dwarf accretes mass from its companion star, the white dwarf can exceed a critical mass known as the Chandrasekhar limit. As the white dwarf reaches this limit, the temperature will rise until it is hot enough to start carbon fusion. Within a few seconds of the start of this nuclear fusion, the energy released is enough to unbind the star in a supernova explosion.

The apparent magnitude of SN2025rbs has peaked at around magnitude 12 by the end of July. In early September brightness had reduced to around magnitude 14.

The telescope array on La Palma, Spain with which SN 2025rbs was first discovered.

 

Image

My original image was processed to ensure a maximum amount of detail and signal from the spiral arms. The consequence is that in a galaxy like this, some of the detail in the core is lost. So I did a quick re-process of the image, making sure I would have the maximum amount of detail from the supernova. Below you can see the final result. The Supernova is very clearly visible. and not only that, it also has a distinctly green colour. That struck me, as the original image showed the supernova as bright blue. Green is not a colour that occurs naturally in the universe. If green stars show up (as they sometimes do), these are typically Lyrae stars. These are variable stars with short periods, often days. When photographing on different nights with different filters, you can get colour anomalies. So when seeing this green colour, I looked back at the data to see if any kind of variability could be observed. I had a decent set of RGB data collected on August 21 and August 28, so I processed those separately. However, both of those images came out with the supernova green.

What could this be, is the supernova actually green at this point in its life-time? Is there still some kind of variability in the system and my frequency of imaging just has not been able to pick that up? Am I doing something wrong during capture or processing? So if anybody would know an explanation,

SN 2025rbs in my image has a persistent lime-green colour, while in the originally published photo the colour was bright blue. Possible sources of error have been checked, and signs for some kind of periodicity have been investigated, but with so far no plausible explanation.

 

Resources

Lots of data is being collected by both professional and amateur astronomers, and information is being collected. For anyone interested to learn more about this object, you may want to check out the information in some of the following links:

Willem Jan Drijfhout
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Photographing Double Stars