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What Would Happen If The Sun Stopped Spinning? | Unveiled

VOICE OVER: Noah Baum WRITTEN BY: Caitlin Johnson
In this video, Unveiled imagines what would happen if the sun stopped moving through space... Join us!

Everything in the universe moves. And everything, to some degree, rotates. But what would happen if our star just stopped? What would happen if the sun refused to turn anymore, and refused to orbit the galactic centre, as well! In this video, Unveiled imagines an all new solar system and an intergalactic disaster!
Transcript

What Would Happen if the Sun Stopped Spinning?


Since the moment of the Big Bang at the dawn of time, everything in the universe has been on the move. The Earth spins on its axis, it orbits the sun, the sun orbits the centre of the galaxy, and the galaxy swirls around and around. All while cosmic expansion goes on and on. But what if one small part of this phenomenon was stopped in its tracks?

This is Unveiled, and today we’re answering the extraordinary question; what would happen if the sun stopped spinning?

There’s really no way in science for the sun to actually stop spinning on its own axis. Today’s question, then, is a purely hypothetical thought experiment. But it’s a fun to think about!

Currently, the sun spins very slowly. But, because it’s made of plasma rather than rock, like Earth is, parts of it spin at different speeds. This is called differential rotation, and it means that some regions of the sun take up to thirty days to complete just one full turn, while others are quicker. Of course, rotation in itself isn’t unusual among celestial objects. Every planet in the solar system rotates, along with moons, asteroids, high energy pulsars from further afield, and even the largest black holes in the universe. Every object rotates because of the motion set off by the Big Bang… and, although it’s comfortably the most massive inhabitant within our particular part of space, the sun is no exception.

The strange thing is, though, that if the sun’s perpetual movement were ever to stop, then it wouldn’t necessarily affect much of anything else. Depending on other factors, the solar system wouldn’t automatically be doomed. The more important part of the sun’s journey through space from our perspective… is that it continues to orbit the galactic centre. If it were to stop spinning but its path around the Milky Way were to be unchanged, then we’d probably be fine. In fact, we could even be safer than usual.

One notable effect that a stilling sun would have for us on Earth would be fewer solar flares. And any solar flares that were emitted should be far easier to predict. This is because the casting of solar flares is usually the result of the sun’s differential rotation. Thanks to the varied movement on our star’s surface, there can be build-ups of energy in and around bright patches called sunspots… and, when these eventually burst, you get a flare. As they are, solar flares can be dangerous on Earth, causing sun storms that are measured in scales just like volcanoes and earthquakes are. Sometimes, although rarely, these storms are powerful enough to knock out Earth’s infrastructure, and they pose some threat to humans – as anyone who’s ever been sunburnt will tell you, we’re a species particularly susceptible to solar radiation.

If the sun stopped spinning then there would be far fewer solar winds to blast this radiation towards us, so we’d naturally see a reduced threat from flares. The reduction in solar winds could dramatically affect the general make-up of the solar system, too, particularly at the outer reaches of the Heliosphere, where the Heliopause currently marks the end of solar wind influence. But in other, even more fundamental ways, a still sun could actually pass by unnoticed. Crucially, a sun that stops turning doesn’t lose any mass… which means it wouldn’t stop being the gravitational centre of the solar system. The movement of all the other planets and asteroids would stay the same.

But let’s zoom out. We know that the sun doesn’t just spin on its own axis; that it also orbits the galactic centre of the Milky Way. Our star system is around 25,000 light years away from the middle of our galaxy, but even at that distance there’s cosmic balance at play. The sun reliably travels through space at around 500,000 miles per hour, and it takes up to 250 million years to complete one full circuit. If any of this was somehow stopped, then we’d have a totally different problem on our hands.

Right away, a sudden stop of the sun could, in itself, cause it to stop rotating. Or at least dramatically change how it rotates. But the force of such an event would do more than just that. It could well be strong enough, for example, to catapult every single planet out of the solar system. Which would be bad news for Earth. Very quickly we’d find ourselves too far away from our star to get enough heat and light. The sun would disappear from view, and Earth would freeze, go dark, and all life would perish as we became a rogue planet. We’d now be orbiting the galactic centre, ourselves, instead of the sun… and that’s a fairly hopeless position for anything in need of a reliable energy source.

Say the sun’s gravity was strong enough to keep us and the rest of the planets tethered to it, however. What then? First off, the shock would likely still cause a major reshuffle to the solar system structure. Even if the sun kept hold of us, then it’s a good bet that we wouldn’t be in the Habitable Zone anymore. So, it’s a good bet that all of the most elemental aspects of life on Earth will have totally changed. But, beyond that, our star system would now find itself in a unique position. Anchored in space, whilst everything else moved around it at breakneck speeds.

Except… we wouldn’t be anchored for long. And soon we’d be on a collision course with the supermassive black hole at the heart of the Milky Way, Sagittarius A-star. Yes, it’s 25,000 light years away from us, but it also has a mass millions of times greater than the sun… so if our star system just refused to orbit, then it could well be pulled in. Admittedly, this wouldn’t be an immediate concern. Even if, on its way toward Sagittarius, the sun somehow reached lightspeed - that’s 186,000 miles per second - it would still take 25,000 years for it (and us) to get there. At speeds that are actually physically possible, it could take millions of years to bridge this distance. So, if we’d somehow managed to impossibly survive everything else up to this point… then it’s highly likely that humans wouldn’t live long enough to see the solar system get spaghettified. It might even be the case that the sun wouldn’t live long enough, and that it would expand into a red giant and consume us before then, too. So that’s… something.

But surely there has to be a bright side? Or a possible solution to this hypothetically terrible turn of events? Silver linings are tough to come by here, but one potential benefit of our doomed journey would be that the stars in our sky would be constantly changing. Our window to the rest of the universe would significantly shift over thousands of years. Indeed, it would only be by observing these changes that we’d even realize what was happening in the first place… so it would be all power and knowledge to the astronomers! But our tour of the Milky Way would at least have us passing by all sorts of new stars, black holes, and even alien planets. Planets that could, perhaps, host life.

So, could we view our untimely voyage to the middle of the galaxy as an opportunity? Couldn’t it prove to be the push we needed to get off of this rock, and onto another one? Being able to accurately predict the future would be more important now than ever before, seeing as Earth’s days would be incontestably numbered. During this world’s fall into the galaxy, we would need to scout new worlds, calculate when we’ll pass closest to them, and work out how to get onto them. And remember, all of this whilst we continually survive against literally all the odds.

If we were to notice our stopping sun and therefore perilous position early enough, then perhaps the best course of action would be to gather as many people as possible and put them on generation ships. But how easy would it be to convince everyone to set sail? At the beginning of all this, it might not feel as though anything of importance was really happening. “So, the stars have slightly changed” we might ask, “what difference does that make?”. Those early, seemingly small variances in the night sky would be informing us that the beginning of the end was here. That our sun had stopped moving through space, was no longer orbiting the galactic centre, and was setting course for an existence-ending supermassive black hole. So, take our advice, if the stars ever do change and you’re offered a ticket for a one-way journey into space… grab it!

But, really, back here on regular Earth, today’s question is relatively simple. If the sun stops rotating on its own axis, then most of everything could well continue as before… and the effects to Earth might even be minimal. But if the sun fell out of orbit… then it could wind up hurtling towards certain death. And we could be taken along for the ride.
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