The last few days have been vastly busy for me with outside jobs, and I am way behind on blog matters! But I did come across some recent research about the movements of stars which fascinated me, and which has prompted this post. It also has the seeds of what could be a fine prehistoric story, which one day might get written.
If you do a quick search for “what is the closest star to our sun” then you will get the reply “Alpha Centauri” (or perhaps, more precisely, “Proxima Centauri” – if you ask Alexa she will give you quite a detailed response). This multiple star system is situated just over four light years from us – for comparison, Pluto is under 5 light hours from the sun. But Alpha Centauri is very like our sun in terms of size, energy, and so on, and is easily visible from the right locations, so has appeared several times in stories.
But what if you then consider the movements of stars over time? All stars near us are involved in a vast circling movement around the galaxy’s centre, but this movement is not regular and orderly in the way that the planets’ movement is around our sun. Stars approach each other and move away, potentially having huge effects on the clusters of planets, comets, etc that accompany them. So what happens if we look forward or backward in time?
So as you can see, Proxima Centauri will get steadily closer to us for the next 30,000 years or so, then lose its role to Ross 248. But none of these stars gets closer to us than about 3 light years, which is comfortably far away and is unlikely to cause any serious issues.
Perhaps you are wondering where the story is in this? We will get there…
Now, these stars are mostly fairly bright, and many of them have been known since antiquity. But in recent years, powerful space-based telescopes like Hubble have discovered that far the most numerous stars in our galaxy are not bright ones like our sun, or super-bright ones like Sirius, but small, dim ones called red or brown dwarfs. These burn extremely slowly, conserving their fuel in a miserly way that means they will hugely outlive our sun. They are invisible to the naked eye even at quite close range (astronomically speaking)… but many of them have planets of their own, and if these planets huddle close enough in, then they could quite easily be habitable. To date, much of our quest for life elsewhere in the universe has looked at stars broadly similar to our own, but maybe we should be looking by preference at these dwarfs?
So… what if we roll back that chart in time to a scale of 70,000 years rather than 20,000, and include the paths of dwarf stars in it (a feat which has only become possible in very recent years). For context, 70,000 years ago anatomically modern humans had already experienced their first large-scale migration out of Africa to other parts of the world, and would soon be doing so a second time. They were sharing the world with Neanderthals and other hominids, and would be for another 30-40,000 years, including various times of interbreeding. They were using stone tools and showing signs of “behavioural modernity” (religious and artistic sensitivity and such like). Slightly earlier, there may have a global crisis involving the Toba supervolcano eruption -some argue that this caused massive population loss, others are not convinced.
Whatever the effects of Toba, around 70,000 years ago a binary star system came very close to us – about 3/4 of a light year in fact. It consists of 1 red dwarf with 1 brown dwarf, both under 100 times the mass of Jupiter. It is called Scholtz’s Star, or WISE J072003.20-084651.2 if you are feeling thoroughly pedantic. Now, 3/4 of a light year is still way outside Pluto’s orbit, but it is inside the region called the Oort Cloud, a loose collection of icy rocks and potential comets that accompany our sun and from time to time journey down into the inner solar system to become visible for a brief time.
Today, Scholtz’s Star can only be viewed in the southern hemisphere, in the constellation Monoceros. It’s about 20 light years away and receding from us. Back then you’d have needed to look in the constellation Gemini (though the shapes would be a bit changed because of stellar movement).
So, would Scholtz’s Star have been visible to our remote ancestors? Well, probably not in its normal state. Even at 3/4 of a light year, it would almost certainly be too dim to be seen with the naked eye. But many red dwarfs are what are called flare stars – their brightness flares up to many times the usual intensity on an irregular basis. And if a flare event happened while it was near to us, then it would have been vivid to our ancestors. Back then, the best time for viewing would have been in the autumn of the northern hemisphere, from the tropics northwards. So my remote European forebears might have stood and wondered at this – although the Europe of 70,000 years ago looked rather different to today’s map!
And here of course is the story – what would these people have made of such a star? Suppose that it had entered our neighbourhood while in quiescent mode – invisible to their naked eyes just as much as ours – and then flared up while close. A new star would have appeared to them, and I wonder what they would have made of it. I don’t expect they had a great deal of time for abstract philosophy back then, but I’m willing to bet they told stories and sang songs – what part would Scholtz’s Star have played in them?