Arp 90 / NGC 5930 and 5929
| Designation(s) | Arp 90, NGC 5930, NGC 5929 |
| Object Type(s) | Galaxy |
| Relevant Catalog(s) | All (Chron), Arp, NGC |
| Arp Category | Spiral galaxies with large high surface brightness companions on arms |
| Obs. Lat/Long | 42° 17', 073° 57' |
| Constellation | Bootes |
| Date and Time Observed | 2025-07-22 00:20:00 |
| Instrument | EdgeHD 8" w/f7 reducer-1,422mm FL |
| Camera | Player One Apollo-M Mini |
| Image Details | Up is 3.6 degrees E of N. Transparency: Fair. Seeing: Fair. Total integration time was 40m 15s. Exposures 15s@300g, No Filter. Dithered and recentered in SharpCap. No guiding. |
| Description | Arp categorizes this galaxy "doublet" as, "Spiral galaxies with large high surface brightness companions on arms". In this case, NGC 5930 (left) is the "spiral galaxy" and 5929 (right) is the bright companion. Arp's recorded remarks include this notation: "Absorption lanes around companion." I interpret this to mean the dark "arm" (in the inverted images) extending down from the top and along the right quarter of 5930's nucleus and effectively surrounding 5929's nucleus. Arp is suggesting that matter is being exchanged between the two of them. Obviously, some sort of strong interaction is taking place. Whether a merger is the ultimate result, or 5929 will emerge as an independent galaxy is unclear. Today, 5930 is classified as a "Starburst" galaxy, one that is unusually active in birthing new stars. Such activity is stimulated by a merger or near-merger, so consistent with the interaction with 5929. 5929 is today classified as a type 2 Seyfert Galaxy, exhibiting a bi-polar radio jet. Today we recognize they contain Active Galactic Nuclei (AGN), centered on supermassive black holes. In the early 1960s, when the Atlas was published, Seyfert was just beginning to publish his work on these galaxies, and black holes were thought not to exist. I do think that Arp missed an important feature of these galaxies, which is what appears to be a tidal tail on the lower left of 5930. It is most visible in my images, especially the positive one. It does appear minimally in Arp's plate. A tidal tail like this suggests 5929 is passing through 5930 from the lower left. |
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