It would be something unprecedented for an accretion driven system to be clockwork precise, especially as the stellar winds from the red giant will be quite variable (that is, mass transfer will not be at a constant rate).
At first the roughly decade long 'high state' looked unprecedented, but it turns out when you look into it that not many people, maybe only one, followed T CrB up until the last outburst. Why should they? Novae didn't go boom twice and this looked far more nova than dwarf nova from its initial outburst (although both concepts will have been ill defined in those days, the latter likely not yet defined at all).
Someone also said somewhere that it's a spectroscopic binary. Well, it is and it isn't. I haven't checked but I'm not sure if it is a spectroscopic binary in the sense that the orbital signature has been detected and measured in its spectra. It is a symbiotic system though, the name given to red stars that have spectra showing what was first thought to be an incongruous bunch of blue emission lines, later decided upon being a red giant star with a hot compact companion, usually a white dwarf for these objects (I don't think any are hot sdB stars, haven't checked).
It wasn't totally unprecedented, RS Oph may have been the first 'known' recurrent nova of the symbiotic subclass (U Sco and T Pyx don't have a red giant companion and are not exactly the same as each other even though sometimes lumped together, other claimed RN aren't necessarily proven as far as I have ever been able to tell, more candidates).
Some of it comes down to taxonomy. Where does an RN start and an SyN end? Lightcurves are mostly different, one very slow to ridiculously slow on fade, t'other fast.
And some are just called Symbiotic Stars that have bright states / small outbursts every few years.
R Aqr has a nebula around it, had an outburst some centuries ago leaving the nebulosity Ced 211 behind, and I think the odd pulse since then (over and above the Mira type pulsational variations : the red giants in Symbiotic Stars do tend to be Mira or SemiRegular variables, which is not the case for T CrB and RS Oph). Is this a longer period RN ready to blow?
Or rather than some evolutionary trend of one sort leading to the other (start at RN, end up SyN, over time for example), maybe they're simply clines, gradients, similar objects differing only due to differing initial conditions (orbital separation, relative rate of evolution of the two stars, possibly independent evolution rather than the enforced evolution some companion stars undergo when the other star evolves and swells to red giant first, all sorts of variable initial states).
For a simpler, and less conjecture ridden and assumption ridden review of such objects use Burnham's Celestial Handbooks. The science in there is often not wrong, just incomplete as newer things are known now. One important feature, however, is he fully describes the systems phenomenologically, ie he tells you what happened, what the things did, and when, and what the aftermath was if known, rather than just chucking theory and dictating dogmatic personally generated computer models at you. Sometimes when you read older descriptions like that you readily find that what some claims have been made not only don't add up, they are "not even wrong", as they seem to not relate to the facts at all on examination, or at least are an extrapolation that can be forced out of the facts but no more than umpteen other diverse extrapolations could, with no means of showing any to be uniquely preferable or demonstrably more accurate.
I initially obtained an outburst time in mid November 2025 plus or minus a long time by simply taking 1946 event - 1866 event and adding the difference to the 1946 event, which leads to Nov 25. It's a completely naive interpretation with no meaning other than using what little data there are in a non-exaggerated extrapolation. The precovery 1700s event may be valid and, somewhat expectedly, shows that there is not a fixed clock at work, however it is unconfirmed, so at best is circumstantial evidence based on near hearsay and the reputation of some past observer, itself only known because the author of the paper defines this reputation (I for one have never heard of this observer before, and nor copies are the original documents provided in the paper, merely references for out of context quotes).
As for the so called 1200s event, well that can't even be shown to be the same object, and some of the description is purely contradictory to what is known about T CrB outbursts (the description of its naked eye visibility lasting months, which is way off, days at best, also that is not likely a case of different explosions at different times, the close analogue RN RS Oph has been caught in outburst quite a few times and it follows the same pattern of short and sweet with fast rise and initial rapid decline (T CrB seems to have a post outburst bump, but this reaches nowhere near naked eye levels).
And stuff like that.
And yes we do have to keep hammering home about the predictions because the media are increasingly full of them, even the so called more serious astronomy targeted media outlets (althoughy why anyone reads stuff like the apocryphal space.com I have no idea, and astronomy has been invariably just spouting out the author(s)/institute provided press release for years, and if they are institute provided you know the final draft came from PR and media relations and NOT the scientists).
If it blows up tonight, or before Sept 2024, it'll just be sheer coincidence.
If it doesn't, well, more prediction will come up, with some excuse based on some re-fudging of the old info. A similar thing happened with this Sunspot maximum. The Sun is going stop, they cried, this maximum will be almost non-existent, and start at that time, and go on that long. After several months of advanced wrongness as far as the prediction went they revised the prediction model and then started use that quite different prediction as the baseline to compare what actually happened with. Of late they seem to be ignoring that that prediction was way off too, a prediction for still nowhere as strong a maximum as is actually occurring.
This hype is another, like 'meteor storms' that are just enhancements, or good events but not "storms", or 'green' comets with massive tails that are actually only seen in their true glory by keen amateurs using dedicated equipment and taking long runs of innumerable frames and then stacking and processing them, and often not visible at all to visual observers unless they live up a mountain in the middle of a desert without a streetlight for ten miles.
This hype makes astronomers look like eccentric idiots, even more so than usual, and when professionals join in (for no good reason often) manages to fool even the amateur astronomers.
Where is the data?! Should be the cry, followed by "Oi! You can't push the data to end up with this theory" because, as the computer often told Kirk "insufficient data".
Short Version : what redbetter said.
Edited by yuzameh, 28 June 2024 - 08:21 AM.
