If the Sun turned into a black hole what would happen to Earth

We bet many of you have wondered, ‘what if the sun were to suddenly become a black hole?’ Would we all get sucked into it and suddenly everything turns black? The short answer, surprisingly, is no! Neither the earth nor us would just get sucked in by a giant cosmic vacuum! What would really happen then? Let’s find out! Here’s what scientists have to say about it:

What would happen to the earth (and us) if the sun became a black hole this very minute?

If our sun suddenly became a black hole right now, it would first shrink down to the size of about 3 km. Yep, only 3 km.

Interestingly (and quite optimistically perhaps), nothing would actually happen to the Earth! The Earth would simply continue on its natural orbit around what used to be the sun. Contrary to popular belief, the Solar System would not be sucked in. This is because even a solar-mass black hole would not exert any more gravitational pull than our Sun already does.

Although all the planets in our solar system including the Earth would keep going on their orbit and doing what they are supposed to do, they would be completely robbed of all sunlight. Since there would not be an actual sun to keep providing heat and light to the planets, unfortunately for us, life as we know it would cease to exist on Earth. For other planets, their atmospheric systems and functions would also change due to the lack of sunlight.

Which makes us think – although black holes are definitely one of the coolest and mysterious things out there, we feel quite happy to have our Sun shining down on us!

What really goes on in a black hole then? Let’s find out!

Scientists are pretty clear now that black holes don’t ‘suck in’ everything around them in their entirety. While as an astronomical and astrophysical event, formation of black holes and properties of black holes are indeed still mysterious, it still does not magically make everything around it disappear. This is in part thanks to a slightly scary phenomenon called Spaghettification (more on this cool phenomenon later!).

Nothing goes into a black hole and vanishes. Instead, things that get too close to a black hole are actually pulled in by the immense gravitational force at the centre. This pull is too strong for anything to escape beyond a certain point known as the ‘event horizon.’ The pull beyond the event horizon is so strong that not even particles or light can escape from it.

As weird it sounds, black holes really do throw stuff back out into the cosmos after gravity pulls things into them. Black holes are like intense patches with very high gravitational pull at the centre, but a little messy when it comes to what they do with the material it gets pulled in.

What is Spaghettification?

Unlike pop culture myths, after things get pulled into a black hole due to the very high gravitational force, not everything disappears. A lot of the material is actually flung out.

Any particle or light that reaches the ‘event horizon’ can’t escape the gravitational pull anymore. After it enters the event horizon it eventually reaches the centre, at which point, the black hole throws or flings out a lot of the material from the object back out through the other side of the funnel. This is called ‘spaghettification’ (yes, like the pasta)!

Cool name? We think so too!

Interestingly, before the material is flung out, it is ‘shredded’ by the black hole in what would be called a ‘tidal disruption event.’ The forces causing the object to shred are so strong around a black hole that it would pull apart any object in a long thick strand, by causing it to stretch out in opposite directions.

Did you learn something interesting today? Is there something you’d like to know more about? Tell us in the comments section below. And don’t forget to share any cool information and trivia you might know about black holes, suns, or spaghettification!

Some time back in the’90’s I wrote a document explaining some things about black holes.  To my amazement, people still read it, and they occasionally send me questions as a result.  I’m happy to answer these when I can, and as long as I’m answering them anyway, I might as well post them here.

The latest is from Chris Warring:

My friend and I are having a debate over the question “If the Sun turned into a black hole, what would happen to the Earth’s orbit?”

I quoted from your article http://cosmology.berkeley.edu/Education/BHfaq.html  “What if the Sun *did* become a black hole for some reason? The Earth and the other planets would not get sucked into the black hole; they would keep on orbiting in exactly the same paths they follow right now….a black hole’s gravity is no stronger than that of any other object of the same mass.”

My friend argued that since astroids impact the Sun then they would also impact the black hole.  This would eventually increase the mass, increase the gravitational pull on the Earth, and place the Earth on a decaying orbit.

I have since read a little on Hawking Radiation, and that black holes evaporate.  I now wonder if the black hole that was our Sun would evaporate, losing gravitational effects on the Earth, and the Earth would end up drifting away from where our Sun use to be.

Here’s my answer:

First, let me say that all of the effects you mention are very small. They would alter the Earth’s orbit a little bit over very long times. When I wrote what I did about the Earth’s orbit, I wasn’t considering such tiny effects. But they’re fun to think about, so here goes.

It is true that, if the mass of the Sun (or black hole, whichever is at the center of the Solar System) goes up, then the Earth’s orbit will be affected. Specifically, it would move to a smaller orbit. And of course the reverse is true if the mass goes down.

First, let’s talk about what’s happening right now, and then consider what happens if the Sun turned into a black hole. Right now, things do crash into the Sun from time to time, increasing the mass of the Sun. On the other hand, there’s constant evaporation from the Sun’s atmosphere (as well as energy escaping in the form of sunlight, which translates into a mass loss via E = mc2). I’m pretty sure that the net effect right
now is that the Sun is gradually losing mass. Taken in isolation, this mass change would cause the Earth to drift gradually into a larger orbit.

That phrase “Taken in isolation” is important. There are other things that affect Earth’s orbit much more than this tiny mass loss rate. The main one is gravitational tugs from other planets, especially Jupiter. I
guess it must be true that the gradual mass loss of the Sun gradually makes all of the planets drift further out, although the details might be complicated.

There’s also the fact that the Earth is being bombarded by meteors. Those presumably slow the Earth down in its orbit. Taken in isolation, that effect would make the Earth spiral in towards the Sun.

I’ve never tried to work out the size of any of these effects. A lot is known about the effects of other planets’ gravitation on our orbit (the buzzword for this being Milankovich cycles). The other effects are much smaller.

Now, what would happen if the Sun became a black hole? Things like meteors would still get absorbed from time to time, but much less often than they do now. That may go against intuition, because we think of black holes as really good at sucking things in, but in fact the black hole has the same gravitational pull as the Sun on objects far away, and it’s a much smaller target, so fewer things actually hit it. So the rate
of mass increase due to stuff falling in will be less than it is now. On the other hand, stuff won’t be evaporating nearly as fast as it does now. (There would be Hawking radiation, but that’s incredibly small, much less than the rate at which atoms are boiling off the Sun now.) So the net effect would certainly be that the black hole would gradually go up in mass, whereas the Sun gradually goes down. The net result would be that the Earth would gradually get closer to the black hole.

But again, the key word is “gradually”: these are really really tiny effects. I’d bet that they’d be too small to have any noticeable effect even over the age of the Universe.