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What If the Sun was a Black Hole?

VO: Noah Baum WRITTEN BY: Nathan Sharp
Sitting at the centre of our solar system, the sun is vital for our planet (and our lives). But what if it disappeared, and was replaced by a black hole? How would our existence change? And what would the future hold for the Earth?

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What If the Sun Was a Black Hole?

Contrary to popular (though misplaced) belief, black holes are not literal holes in space. The actual confirmed science behind them isn’t quite as crazy as wormholes and all that, but it’s still plenty interesting – and there’s still a lot we don’t know. Some black holes happen when a massive star – much bigger than our own – dies. These stars collapse and form small yet incredibly dense areas of spacetime, with an extremely strong gravitational pull. They get their ‘black hole’ name because they eat up all the light around them, along with everything else. But in fact, their indiscriminate destruction is actually what allows us to observe them in the first place. When matter falls into one, an incredibly bright accretion disk forms around the edge, which we can use to scientifically calculate where the black holes are.

But what if our closest one was right where everyone could see it? What would happen to us, Earth and all our planetary neighbours if our sun was actually a black hole?

First off, this particular alternate reality is purely hypothetical, and not actually possible. Our sun is simply far too small and doesn’t contain enough matter, for anything like it to realistically happen. And, if our sun had always been a black hole, then we probably wouldn’t even be here to discuss it. But, in the interests of our own imaginations, let’s envisage that the sun randomly collapses into a black hole overnight. What would happen?

You might imagine that the end of all things would set in pretty quickly, that we’d simply be sucked into our newly-acquired black hole centrepiece immediately, and that we’d all instantaneously die. But surprisingly, no. In fact, the Earth, other planets, and nearby celestial bodies would all continue to orbit around it, just as they do our current sun. The black hole would contain the exact same gravitational pull as the sun did, and would be no closer to the planets than the sun is right now. So, it’s as you were, minus that bright, essential-to-life light in the sky.

Don’t believe us? Just take a look at the center of the Milky Way (or most spiral and elliptical galaxies, for that matter). At the heart of most of these galaxies is a supermassive black hole. The Milky Way’s (and therefore ours) is called Sagittarius A-star, and it’s about 26,000 light years away from us. Sagittarius A-star, like all supermassive black holes, does not relentlessly suck in everything within the vicinity. Rather, it shapes our galaxy by exerting a gravitational force which results in a rotating disk of stars, planets, gas, and dust. Just as this disk of matter spins around a supermassive black hole, so too would our planets orbit around what was once our sun.

But that doesn’t mean that life on Earth would carry on unchanged, as well. The first and quite obviously noticeable effect would be the lack of sunlight and heat, as the Earth and the entire now not-so-solar system would be plunged into darkness. For energy, we’d be forced to rely on fires, fossil fuels or electricity, though solar powered products would obviously no longer work. All of which means that energy bills would skyrocket, but that would be the least of our concerns.

While we wouldn’t immediately freeze, global temperatures would drop to below zero degrees Fahrenheit within just a week or two, before tumbling to minus 100 degrees or lower within a couple of years. Entire ecosystems would descend into chaos, meaning anything that could survive the chill would struggle to find food. Plants would no longer be able to perform photosynthesis and would quickly die, sending the entire food chain into disarray. Mass species extinction would likely set in within just a few weeks, and eventually the top layers of the Earth’s water would freeze – turning our planet into a very large and inhospitable snowball.

Earth could also be bombarded with meteors. Our sun currently attracts countless celestial bodies, including meteors, which burn up even if they stray too close to the star. While the black hole would retain the same gravitational pull as the sun, the no-go zone for space rock would be much, much smaller, resulting in more meteors careening off into the great beyond. So, while daily meteor showers would still be unlikely, Earth could be hit at a far greater frequency than it is today.

Luckily, some exceptionally hardy humans could be around to witness these incredible sights. We have science on our side, after all! One survival plan could see us all coalesce into areas powered by geothermal energy, such as in certain parts of America, New Zealand and famously across most of Iceland. In theory, we could harness the Earth’s internal energy stores for hundreds of years, to power a proposed promised land for everyone. That said, it would be an exceptionally tight squeeze, in the unlikely event that every human survives and makes it to a safe zone. Taking into account the area of Iceland as an example, and the global population, we’d have around 75,000 people per square kilometer – meaning it’d be almost 3x more densely populated than even the busiest global cities today. Seeing as so much of the planet will’ve been robbed of all its resources, keeping everyone safe, happy and healthy would be almost impossible – even if habitable environments were created.

Were the sun to magically morph into a black hole, it’d clearly cause catastrophe. But all hope wouldn’t quite be lost. Sure, the Earth would be bathed in darkness, the planet would grow unbearably cold, most of life would quickly go extinct, large swathes of humanity would probably die, and those who survive would do so in seriously cramped and chaotic conditions. But it’s not all bad. The planets themselves would largely continue to orbit as usual, without being suddenly and irretrievably sucked into the scary black hole at the centre. So, all wouldn’t be lost, and us humans might even be able to adapt. Maybe.

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