It is summer in the northern hemisphere. For most people, that means beach parties and bocce ball, but for me, it means war. I must don my gooey armor of sunscreen and once again do battle with my mortal enemy — the Sun.
The Sun always wins eventually, but my pasty white skin puts up a valiant fight before I must retreat into the shadowy apartment from whence I came.
But while I may be no match for its nuclear fire, our Sun isn’t particularly noteworthy. It’s not the biggest star in the galaxy, and it’s not going to become something cool, like a black hole, someday. It’s just a middle-aged, yellow dwarf star of average size, inhabiting a part of the galaxy of no real significance. It’s downright boring in the grand scheme of celestial objects.
But it’s the only star we’ve got.
It wasn’t always that way, though. Billions of years ago, the Sun had a twin. And it’s still out there somewhere. And it might be trying to kill all of us — not just my pasty self.
This is a giant molecular cloud. It’s full of gas, dust, and baby stars. Our Sun formed in a molecular cloud very similar to this one about 4.6 billion years ago. Compressed by the shockwaves of a nearby supernova, a volume of hydrogen gas collapsed onto itself. The cloud became so dense and hot that the gravitational pressure inside of it overcame the electrostatic repulsive force between protons. This force crushed the hydrogen atoms together and initiated nuclear fusion. This was how our Sun was born — in a thermonuclear detonation.
But it wasn’t the only explosion that day. Not too far away, another star ignited as well.
This star was the Sun’s twin.
Not identical, but conceived of the same dust and gas, under the same conditions, in the same giant molecular cloud.
Most of the stars we can see aren’t alone
Stars have companions. The majority of solar systems have multiple stars within them. For a long time, we wondered whether these multi-star systems started out as singletons, like our solar system, and whether, over time, singletons became captured or entangled in each other’s gravity, creating the multi-star systems we see today.
Or maybe they were born that way.
Contemporary computer-generated models of the physics at work in these giant molecular clouds during the formation of stars, like our Sun, seem to suggest that they were born this way..
Because of the shape of these stellar birthplaces, two cores are created when the cloud undergoes collapse. This would indicate that all stars are born with a twin — even our Sun.
But the idea that our Sun had a twin isn’t a new idea
In the 1980s, scientists began to notice a pattern in Earth’s history. Every 26 million years, or thereabout, a significant reduction in biodiversity could be observed in the fossil record. These mass-extinction events seemed to occur on a schedule, as if whatever was causing them was cyclical. A distant star, too dim to be observed by the naked eye, on a 26 million year orbit around our Sun, could theoretically come close enough to the solar system and disturb the orbits of the comets lying dormant in the Oort Cloud or Kuiper Belt. These comets would then rain down on the inner solar system, impacting the Earth and causing mass extinctions.
The hypothetical star was called Nemesis — named for the Greek goddess of retribution. Nemesis has been variously postulated to be a small, dim star, or the remnants of a star that has exhausted all its nuclear fuel, or even a rogue planet larger than Jupiter. Whatever it was, if it was the Sun’s twin, it was an evil twin. But all attempts to spot the culprit have failed.
Further investigation into the fossil record has cast doubt on the regularity of mass extinctions. Any plausible orbits of an unseen star that could wreak havoc on the solar system, it has been deduced, would be inherently unstable. You can’t have cyclical extinction events if your Nemesis star can’t stick around long enough to cause them.
Despite the lack of evidence, Nemesis still pops up in the news from time to time, heralding dramatic climate shifts, asteroid impacts, and other typical signs of the apocalypse.
But even if Nemesis doesn’t exist, the Sun’s real twin is in all likelihood still out there somewhere — but very far away
According to the most recent models on stellar development, our Sun and its twin would’ve only spent a few million years together before slowly drifting apart. The Sun’s twin, at this point in time, could be thousands of light years away. Conceivably, we could find it by searching for stars that are the same age as our Sun, with the same spectral features, but there’d be no way to know for certain whether any particular candidate star was actually our Sun’s twin.
So, the Sun’s long-lost twin will most likely remain long lost.
The real tragedy here might not be that the Sun has an evil twin lurking in the outer edges of the solar system, bringing death and destruction. The tragedy is that it doesn’t. Our star, despite having so much in common with so many other stars in our galaxy, is most likely alone, has been for much of its existence, and will in all likelihood stay that way until it exhausts its nuclear fuel and dies.
But that’s also what makes it unique.
If events had progressed differently, and the Sun and its twin had stayed together, our solar system would be a very different place. The planets as we know them would most likely not exist. Even if life had managed to find a foothold, humans definitely would not be here. At least I wouldn’t. My pasty white skin can barely handle one Sun.
Obviously, the Sun is a big ball of hydrogen and helium. It can’t feel lonely. But I can rest assured, in the dark confines of my apartment, that the Sun will seize another glorious victory dimmed by an unbroken and remarkable solitude.
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