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Comment by pbhjpbhj | Hacker News Reader

>"According to their calculations, the star was right in the center of the nova shell on the day the Koreans saw a mystery star, which means it caused the cosmic explosion."

Hmm, or it was in a different plane and is many light years from the nova and some other star, which died, or is too faint to see, or isn't charted, was the cause of that particular nova.

Isn't this classic "correlation is not causation" stuff?

I was expecting to find how they showed the Koreans recorded the position so accurately it could be matched - to the day - with a projected location of a star for which we have 3 data points?

The conclusion (in the abstract) sounds more like a postulate. It seems perfectly reasonable, but does it really follow logically from this single instance?

Presumably, if the conclusion is sound, there are enough records of novae that one can now draw _many_ star trajectories through groups of novae each caused by a single star?

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Binary systems that produce classical novae (like this one) don't "die". Moreover, the star that they identified is a confirmed binary system with an evolved late-type star and a white dwarf, which is precisely the kind of system that you need to produce a classical nova. (Part of the paper is data demonstrating this, including the orbital period -- about half a day -- of the system). In addition, it has produced minor ("dwarf nova") outbursts several times in the last century, which is what you'd predict for a system in the "hibernation" period between classical nova outbursts.

So it's not just the spatial match-up -- there's a lot of additional supporting evidence that this binary system is in fact the one what done the deed.

Isn't this classic "correlation is not causation" stuff?

It isn't. There are only a few dozen intragalactic novas per year. They've been looking for this one for a while and so far this is the only candidate anyone's found.

one can now draw _many_ star trajectories through groups of novae each caused by a single star?

That's a bit like saying you can draw many trajectories of cars that could have been in a crash while the smoldering wreckage is sitting by the side of the road.

We're looking at 600 years back, so are you saying there's 18000 novas to examine (30 per year) across that period?

Their conclusion in the OP was AIUI that _many_ stars produce novae serially. So we should surely be able to match series of novae (along a stars trajectory).

Do you know are English language details of the historic Korean record available (are they in the paper)?

http://www.cbat.eps.harvard.edu/nova_list.html shows very few recorded novae, is this a listing including the dozens per annum you mention?

https://arxiv.org/abs/astro-ph/0501331 includes a table (as far as I know, exhaustive) of historical Korean nova records.

Fascinating, I was expecting it to be in hanguls rather than Chinese characters - never really considered astronomy as having an overlap with history quite so much as this before. Thanks for the link.

Their conclusion in the OP was AIUI that _many_ stars produce novae serially. So we should surely be able to match series of novae (along a stars trajectory).

The time between classical nova outbursts is estimated to be on the order of 10,000 years, so the previous outburst of this particular nova was probably long before the development of writing.

In addition, it likely takes only a couple of thousand years for the expanding shell of gas to fade from visibility, so it's probably not possible to find the traces of previous outbursts along the trajectory (although that would be cool).

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