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Our sun has been burning for 4.5 billion years, but it was not the first of its kind – those stars ...
2020-09-22 09:00:00

The Very First Stars
A Journey into Space-Time

"Falling Stars", Franz von Stuck, 1912/Wikimedia Commons (public domain)
The Very First Stars
The Very First Stars

As the world gazes into the future with a sense of uncertainty, let us take a moment to peer back into the distant past. The stars that came into existence at the dawn of the universe turn out to have been vastly different from those shining in today’s sky.

Read in 6 minutes

These days, we can hardly be certain of the future, or even the present. So maybe we should seek comfort in one of the bygone eras? Preferably taking our thoughts back to times that we don’t actually remember, so that we can relish them more easily. Perhaps the 1960s or 1970s? Granted, that’s tempting, but many people who witnessed those decades firsthand are still among us, after all, and they argue that things actually didn’t look so rosy back then, in Poland or elsewhere. So, maybe the inter-war years? Let’s not be so naïve – back then, most people in Poland lived in poverty, and only the chosen few got to party in Warsaw’s famous Adria Café. What about the times of the Polish-Lithuanian Commonwealth? Wrong, again. The shameless exploitation of peasants is a disgrace to that period, and the same goes for the preceding era of knightly chivalry.

So let’s travel further back into the past. To the times of Athenian democracy – surely, that’s an unassailable ideal! But alas, it was built on slavery, so it’s downright barbaric from today’s perspective. Maybe prehistoric times, before the invention of agriculture and the advent of patriarchy? Sounds enticing, but the people back then rarely lived to be 40 (at my present age, I’d have been already dead, and I still have a lot of plans for my future).

In that case, let’s go even further back to an era in which there were no people. If we stop around 200–300 million years ago and look around, we will see that the land on Earth, now split up into continents, then formed a single supercontinent called Pangaea. What a wonderful vision of a united world! But if we look more closely, we’ll be astonished to see that the world, united as it was, did not live in peace. Big organisms gobbled up the small ones, and the small ones quietly ate the big ones, too, whenever they got the chance. That’s the way things usually are.

If we delve deeper and deeper into the abyss of time in search of a golden era, we will finally find ourselves in the epoch in which the Earth was dominated by plants – which needed light, water and carbon dioxide to survive. But these innocent things actually also have a lot on their conscience; the oxygen that they produced killed off most of the earlier anaerobic organisms. That event is now called the Oxygen Catastrophe, the first great extinction event known to science.

To avoid having to witness such graphic scenes, we’ll have to go even further back, to the times before the appearance of life. But will we find anything to our taste there? To be honest, a big cloud of gas from which the sun and planets were just starting to form could be interesting only to experts. Looking at this shapeless fog, we impatiently press the rewind button again, holding it for longer, and stop way back in the period shortly after the Big Bang. A lot has been said and written about these times, when elementary particles were squeezed together in a hot and seething swarm, but no-one except expert physicists could say with any dose of certainty what was happening in that hodgepodge. Mere mortals, not armed with sophisticated theories, feel lost there.

But maybe we’ve hurried too much into the past, travelled this long distance too fast? Yes, we should have stopped a little earlier. After all, there’s at least one era in the history of the universe whose monumental, raw beauty will not leave anyone indifferent. That’s where we should direct our imagination.

This was a time when the universe was still very young. Today, it’s nearly 14 billion years old. Back then, it was only 100 or 200 million years old, and that was when the first stars started to shine. They were completely different from the sun as we know it, different from any of today’s stars. Compared to those first stars, today’s stars are like military reenactment groups as compared to the actual mediaeval Battle of Grunwald. The first stars were a lot bigger, hotter and brighter. Their mass ranged from around 100 to 1000 solar masses. Their surface temperature was 20 times higher than the temperature on the sun. Their radii were tens of times wider, and their luminosity reached tens of millions of solar units. (I have taken these figures from materials from Yale University, rounding them up slightly, in keeping with the standard custom among journalists.)

We could say that the life of those stars was short but intense. They were white hot, so they burned quickly. Three million years, and bam! They were gone. To put this into perspective, the sun has been shining for 4.5 billion years, and it’s bracing itself for another five billion. That’s because it’s glowing with moderation, wisely conserving fuel rather than racing through it at breakneck speed.

The narrative’s logic would probably dictate that those giant stars should be surrounded by huge planets, inhabited by ultragigantic dinosaurs or by massive humanoids with eyes the size of water wheels. But that was not the case. No planets, whether inhabited or uninhabited, existed at that time. For one simple reason: there were no elements other than those that appeared shortly after the Big Bang. In other words, in the whole universe there was only hydrogen and helium (plus a little bit of lithium and maybe also beryllium). And hydrogen and helium alone are not enough to make a planet, let alone life as we know it.

It was the absence of elements other than the lightweight ones that caused the first stars to burn so quickly. The heavier elements present in the sun slow down thermonuclear fusion. The reason why the earliest stars swelled to such unprecedented dimensions was exactly the same: a lot more hydrogen and helium is needed to start fusion if there are no heavier elements, such as carbon, oxygen, iron or other ingredients in the ‘stellar barbecue’ mix.

All these other chemical elements originate in stars, at the end of their lives. Logically, then, those elements must have been absent from the first stars. It was not until the pre-stars burned out, collapsed, and exploded as supernovae that the whole periodic table of the elements became spattered throughout the universe. These spatters eventually contracted into dense clouds and formed other stars, but even they didn’t belong to the same generation as the sun – it appeared yet another generation later.

Here, it must be pointed out that the sun’s generation is traditionally called Population I by experts. Those stars were formed after our galaxy came into existence. The intermediate generation was Population II – those were the contemporaries of our galaxy. And the first, biggest and fastest burning giants formed Population III. They appeared before our galaxy was formed or, strictly speaking, our galaxy came into existence thanks to them – one of those giants left behind a black hole that gave rise to the black hole now at the centre of the Milky Way.

That’s the way things happened. Well, most probably. Although we can still observe Population II stars, the whole of the heroic era of Population III is only a presumption. We assume that such a generation existed for the same reasons as those we’ve just described – because elements heavier than hydrogen and helium must have originated somewhere. There are plenty of those heavier elements in the Population I stars, and they are still present in the stars of Population II, though in smaller amounts. But none of them, as we believe, were present in the stars of Population III (or the chronologically first generation).

These days, we can hardly be certain of the future. But the James Webb Space Telescope, the ultrasensitive successor to the Hubble Space Telescope, is still scheduled for launch in 2021. It is not out of the question that its cameras will manage to glimpse a star from the oldest generation. In order to do so, we will have to direct the machine’s eye at one of the most distant corners of the universe, from which light has to travel to us for nearly 14 billion years.

If the mission succeeds, it will be an unprecedented triumph of science and technology – to look so deep into the abyss of space-time. But will this insight prove any more amazing than the fact that we can already reach so far back with our imagination? We can simply close our eyes and marvel at the first stars: huge, hot, impatient, and deprived of any elements heavier than hydrogen and helium (well, maybe except for a little bit of lithium and beryllium).


Translated from the Polish by Daniel J. Sax

We keep track of the latest scientific reports, delve into the unknown and read pages and pages, all so that we can share our new-found knowledge with you. We check the facts, add up the equations and compare the findings. That is why your support matters to us. Thank you for being with PRZEKRÓJ Foundation.

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