As a summer student at Kitt Peak Observatory in 1974, I had the honor of working with Art Hoag. Not just a brilliant astronomer and a super efficient observer. Art was a true gentleman of the old school: kind to students and quite progressive. Forty five years ago, over night-lunch at the observatory, he told us of the importance of bringing into astrophysics more women, minorities, gays, and foreign students.
For those not aware of this book, I just looked it up and found a video enactment of it starring cliff Stoll on Youtube. Started out slow, but after a few minutes in when they started getting into the details I was hooked. Looks like I just lost an hour tonight, lol.
Very cool that there’s a second ring galaxy you can see by looking through the first one! And here I was not even knowing ring galaxies existed until today!
Maybe that is a selection effect. Objects like this that are more inclined will tend to look more like regular galaxies so will not be identified as ring galaxies so easily.
well sure.. but if one average an arbitrarily chosen vantage point (ours) sees only one of these so well, then we can infer that many other arbitrary vantage points see none. and that would be sad.
(i know the article mentions others, so this might not hold up to a full cataloging of our night sky)
A classic! I’m working on the Culture novels now, which have their own variant (“orbitals”), minus the shadow squares or central star. Can’t recommend them enough, so far.
Orbitals, while enormous (greater surface area than earth), are much smaller. The Culture novels do have Ringworld-sized rings as well, though. E.g. from Consider Phlebas, flying under the orbital Vavatch: "It was like flying upside-down over a planet made of metal; and of all the sights the galaxy held which were the result of conscious effort, it was one bested for what the Culture would call gawp value only by a big Ring, or a Sphere."
If I understand correctly, the middle part far out-masses the ring. If the middle part were not centered, then the ring could continue to peacefully orbit it, as the planets orbit the sun, even though their orbits are not (quite) centered on it.
It seems the story of how this galaxy formed remains unknown.
> Many of the details of the galaxy remain a mystery, foremost of which is how it formed. So-called "classic" ring galaxies are generally formed by the collision of a small galaxy with a larger disk-shaped galaxy. [...] However, there is no sign of any second galaxy that would have acted as the "bullet", and the likely older core of Hoag's Object has a very low velocity relative to the ring, making the typical formation hypothesis quite unlikely. [...]
> A few other galaxies share the primary characteristics of Hoag's Object, including a bright detached ring of stars, but their centers are elongated or barred, and they may exhibit some spiral structure. While none match Hoag's Object in symmetry, this handful of galaxies are known to some as Hoag-type galaxies.
I offer no hypothesis of my own (not least because this is outside my field), but it does seem odd to me as well. Is it possible that our mechanical intuition fails at such a large scale?
My completely speculative thought is that a smaller galaxy rotating the other direction collided near the center. The angular velocities cancelled in the inner region and that all collapsed to a dense slower core. That just seems unlikely, but then again it's an unusual galaxy.
