NGC4631 is a barred spiral galaxy, seen edge-on, located about 30 million light years from us. It is somewhat misshapen, due to its gravitational interaction with it's immediate neighbor, NGC 4627 (the small blob just above it in this image) and NGC 4656 (not in this field, but almost). The pink regions are ionized hydrogen gas, indicating star-forming regions; perhaps the intense star formation is related to gravitational interaction among the galaxies; toggle between the two versions to see how adding data taken through a filter which passes only the emissions of ionized hydrogen (hydrogen alpha) enhances these regions (they are not really visible in my image absent the use of the Ha filter). As part of the gravitational interaction between NGC 4631 and NGC 4627, note the faint bridge of stars between the two.

The dominant blue color in the disk is from energetic young stars being formed in the arms of the galaxy; the yellow is from a combination of older stars inhabiting the core, and light from starburst happening there.

NGC 4631 is a large galaxy, with a diameter of about 130,000 light years (about the same as our Milky Way).

The entire field of the photo is about the same width as a full moon. As is often the case, the field in the uncropped images is littered with smaller (meaning far more distant) galaxies; I always like seeing how many galaxies there are in our universe!

Technical Information:

L(HaR)GB: 400:840:225:240:260 (a total of over 32 hours of exposures); the luminance layer consists of 56 fifteen-minute images using a luminance filter; the R channel is a blend of 15 fifteen-minute images taken through a red filter and 20 twenty-minute images taken through a hydrogen-alpha filter; G consists of 16 fifteen-minute images taken through a green filter, while B is the combination of 13 twenty-minute images taken through a blue filter.

Equipment: RC Optical Systems 14.5 inch Ritchey-Chrétien carbon fiber truss telescope, with ion-milled optics and RCOS field flattener, at about f/9, and an SBIG STX-16803 with internal filter wheel (SBIG filter set), guided by an SBIG AO-X/STX Guider, all riding on a Bisque Paramount ME German Equatorial Mount.

Image Acquisition/Camera Control: Maxim DL, controlled with ACP Expert/Scheduler, working in concert with TheSky X Professional Edition.

Processing: All images calibrated (darks, bias and sky flats), aligned, and combined in Pixinsight. Color combine in Pixinsight. Some finish work (background neutralization, color calibration, deconvolution with Blur XTerminator; noise reduction using Noise XTerminator, gradient removal, and blending the Ha data with the broadband data) done in Pixinsight; some finish work (LRGB combination, contrast and saturation adjustment) was done in Photoshop CC.

Location: Data acquired remotely from Sierra Remote Observatories, Auberry, California, USA.

Date: Images taken on many nights during March and April of 2024. Image posted October 19, 2024.

Date: Image scale of full-resolution image: 0.56 arcseconds per pixel.

Seeing: Generally very good

CCD Chip temperature: -25C

Copyright 2024 Mark de Regt