NGC 7331
NGC 7331 – a star explodes in the light of a distant spiral
A small bluish-white point beside the bright centre turns this image into a record of a changing sky: SN 2026aaiv, a new supernova in NGC 7331. The marked source belongs to the distant galaxy. Its light reaches us after travelling for roughly 45 million years from the direction of Pegasus.
A new point of light in September. The ATLAS sky survey discovered the event on 1 September 2026 as ATLAS26krw, at 17.33 ± 0.19 mag in the ATLAS orange band. No source had been detected there the previous day. The Transient Name Server now lists it as Type Ia: the thermonuclear explosion of a white dwarf. That classification does not yet establish which kind of binary system triggered it.
What its spectrum reveals. Nico Montigiani and Massimiliano Mannucci observed it on 4 September at the “Margherita Hack” Observatory near Florence. The blueshifted Si II silicon feature at 6355 Å indicated 13,500 ± 500 km/s for the expanding material, about 4.5 per cent of the speed of light. Comparison with reference spectra suggested an early phase, roughly ten days before maximum light at the time of the spectrum. This is a spectral phase estimate, not a measurement of maximum brightness in this image. Research checked on 11 September 2026.
The setting of the explosion. NGC 7331, also Caldwell 30, presents a strongly inclined disk: dark dust lanes cross the warm central region, with bluish spiral arms farther out. William Herschel discovered the galaxy in 1784. Its size and mass resemble those of the Milky Way. The smaller galaxies around it form the apparent “Deer Lick Group”, but lie far behind NGC 7331. The image brings together foreground stars in our own galaxy, the nearby spiral and a much more distant backdrop of galaxies.
Where in the sky
The rectangle is this image's real field of view, with its measured rotation — not a symbol. Constellation figures and star positions come from SIMBAD.
2 entries sit within 24° of each other here — click a field to jump to it.
Crops
Spiral & dust
NGC 7331 – dust against the glowing centre
10.0′ × 5.7′·22h 37m 04.82s +34° 24′ 44.7″
Approximately 10.0 × 5.7 arcminutes. The inclined view gives NGC 7331’s disk a strong sense of depth: dark dust lanes lie across the bright central region, alongside bluish, knotty spiral arms. Young, hot stars shape the light of the arms; towards the centre, the light of countless stars blends together.
Near the centre, SN 2026aaiv adds a bright point. Its changing brightness and spectrum establish its identity as a supernova; colour alone cannot do that.
SN 2026aaiv
SN 2026aaiv – an explosion reduced to a point
1.3′ × 1.4′·22h 37m 05.71s +34° 24′ 36.7″
This close-up spans about 1.35 × 1.44 arcminutes. The supernova lies at the TNS position 22h 37m 05.618s / +34° 24′ 35.37″ (J2000/ICRS), approximately 20″ east and 21″ south of the galaxy’s centre in projection.
The optional ring identifies the supernova’s point of light. What we see is the unresolved light of the explosion; its expanding ejecta cannot be distinguished as a structure in this image.
Background galaxies
Apparent companions – galaxies far beyond
8.2′ × 4.2′·22h 37m 24.93s +34° 25′ 49.7″
Approximately 8.2 × 4.2 arcminutes. NGC 7337 is at upper left, the conspicuous elongated NGC 7335 at lower right, with the smaller NGC 7336 beside it. Their positions were checked against SIMBAD using the image’s astrometric solution. NGC 7340 lies outside this crop, near the top of the full image, where it is also labelled in the overlay.
They look like small companions of NGC 7331, yet lie roughly an order of magnitude farther away. The familiar name “Deer Lick Group” mainly describes their arrangement on the sky.
Acquisition and processing
Broadband imaging with a Askar 120APO at 840 mm focal length and a ZWO ASI585MC Air. The integration contains 48 light frames: 21 × 120 s and 27 × 180 s, totalling 2 h 3 min, at gain 200. Acquisition provenance embedded in this final image records the interval from 9 September 2026 at 22:24 UTC to 10 September at 22:23 UTC. The integration comes from the documented 2× drizzle run; the final version was prepared in Photoshop.
The field spans approximately 22.1 × 14.7 arcminutes. The optional overlay identifies the supernova by projecting its TNS catalogue position onto the astrometrically solved image. The ring is a position marker, not a resolved shell of ejecta. The discovery magnitude is an ATLAS measurement; no independent magnitude was derived from this stretched image.