By Stuart Gary
Black holes are the stuff of science and sci-fi and the line between fact and fiction can often be blurred. So, here are some common black hole myths that you'll never be sucked into again.
"Most people know that a black hole is a very small volume of space with a lot of stuff in it, so that its gravity is so strong nothing can escape from it, not even if it's travelling at the speed of light," said Dr Amanda Bauer, astronomer at the Australian Astronomical Observatory.
But there's a lot more to know about black holes than that.
Myth 1: Our Sun will become a black hole when it diesNo, our Sun isn't massive enough to become a black hole. Instead in about 6 billion years' time, the Sun will expand to become a red giant star with a diameter stretching maybe as far as Earth's orbit.
The Sun will then puff off its outer gaseous envelope, leaving behind its white hot stellar core, and become a white dwarf.
If the Sun was a far more massive star then it would have a more violent death, exploding as a supernova and leaving behind a super-dense object called a neutron star.
"When a star maybe 10 times more massive than the Sun goes supernova, its core collapses beyond the neutron star phase to form an even denser object called a stellar mass black hole," Dr Bauer said.
Myth 2: Black holes aren't real because you can't see themBlack holes can't be seen because light can't escape from them, but that doesn't mean they can't be detected using other means. Astronomers can see the effects of black holes on the space around them.
"While we can't actually see them directly, mathematically we have known about black holes since Albert Einstein's time, since the early 1900s," Dr Bauer said.
With modern telescopes we can see how black holes affect the stars orbiting around them.
"We have something at the centre of our Milky Way galaxy called SgrA* that doesn't produce any light, and we can watch individual stars going around it, not in nice circular orbits, but in highly elliptical, elongated paths," Dr Bauer said.
We can watch maybe a dozen of these stars orbiting around SgrA*, Dr Bauer says, and use very basic physics equations to calculate the mass of any of these stars and the thing they're orbiting around in order to account for the motion of that star.
"And you find that there is something there that's over four million times the mass of our Sun but in a tiny area that produces absolutely no light. There's nothing else we think that it could be other than a black hole."
Myth 3: Black holes will suck up all the matter in the universe like a giant vacuum cleanerFortunately, this isn't likely to be true.
This is because you have to be very close to a black hole to feel the strength of its gravity, and gravity gets weaker the further away you get, Dr Bauer said.
"If the Sun could magically turn into a black hole (which as we already pointed out it can't), then all its stuff would get shoved down into a tiny little volume maybe a couple of kilometres across.
"Think about what would happen to Earth, the Sun would still have the same mass if it were a black hole instead of a star. Earth also still has the same mass and still be the same 150 million kilometres away from it, and gravitationally speaking the only things that matter are your mass and how far away you are."
This means gravitationally nothing changes, Earth has no idea that the Sun has suddenly changed into a black hole and so it just continues its orbit. And the same thing happens on the larger scale of the galaxy.
Mind you, things would be a lot darker on Earth.
"Remember at the centre of our galaxy we have SgrA*, we have this supermassive black hole that's there and our Sun just orbits around it with the rest of the galaxy," Dr Bauer said.
"The Sun doesn't care what's there creating that mass. There are also hundreds of billions of stars between us and that black hole, so gravitationally we don't care what it is. You have to be very close to the black hole to get sucked in."
Myth 4: Entering a black hole takes you through a wormhole to another place and timeMathematically, this is possible. But there are several problems with this possibility, including spaghettification.
"You could potentially have a wormhole that ties you to another place in the universe and maybe you'll pop out of a white hole on the other side," Dr Bauer said.
But these are very delicate solutions. If anything happens to the black hole, if you disturb it by something falling into it, or if the black hole's spinning, then this solution falls apart.
"Mathematically it's possible but it's not very likely," Dr Bauer said.
And it's unlikely that we'll be able to ever find out.
"We are never going to be able to measure this scientifically because if we send something into a black hole we could not get a signal out to tell us what's happening," Dr Bauer said.
"The signal will travel at the speed of light, and that's not fast enough to escape the gravity of a black hole."
Also, any object falling into a black hole would experience huge amounts of gravitational force as it fell closer to the event horizon, the point beyond which light can no longer escape a black hole's gravity.
For example, a clock falling into a black hole would feel a far stronger gravitational pull on the side nearest the black hole than the part further away from the black hole, so the clock would slowly start to elongate and be pulled apart.
"We have a word for this. We call it spaghettification, as you get stripped down to your individual atoms as you get pulled into the black hole," Dr Bauer said.
If somehow the clock magically survived spaghettification and you were able to see it ticking, you would see the ticking appear to slow down as it fell towards the event horizon. This is because time slows down as you get closer to a massive body, like a black hole.
"But from the clock's perspective time is still ticking at the same rate it actually doesn't seem like anything happened," Dr Bauer said.
Myth 5: Supermassive black holes form when a massive star diesThere are supermassive black holes in the centres of most galaxies — but the way they form is more uncertain.
"One possibility is that the very first generation of stars which were made out of almost pure hydrogen and helium from the Big Bang 13.8 billion years ago were bigger than today's stars, maybe hundreds of times the mass of our Sun," Dr Bauer said.
These stars were so hot and huge that they burned through their nuclear fuel supplies in just a few million years before going supernova and forming primordial black holes.
Formed in regions where lots of gas was collecting and forming the first galaxies, these primordial black holes probably sank to the centre and grew over time, eventually forming supermassive black holes, Dr Bauer said.
"Another possibility is nearby black holes merged to create progressively bigger black holes, so you get this merging of black holes, which over time form supermassive black holes.
"The big challenge is that we haven't seen any intermediate-sized black holes, we haven't seen anything between stellar mass and supermassive black holes, so we're not sure yet whether this is the formation process, but it's a good theory."
Myth 6: The universe will be consumed by black holesFeel free to breathe a sigh of relief because this is not likely to happen.
"The universe does go through various transitions in its future but this is over trillions of trillions of years in the future," Dr Bauer said.
"Eventually stars won't be able to form any more, but black holes are very long-lived and will continue to absorb material becoming more massive, but they don't last forever."
Black holes slowly evaporate through a process called Hawking radiation, but this will take trillions of years.
"So in this scenario of the fate of the universe, all the stars will slowly burn out, no new stars will form, and you'll be left with a black hole epoch, dominated by these supermassive black holes which will slowly evaporate," Dr Bauer said.
"In the end what we're left with is a big, huge, vast space with lots of tiny little elementary particles floating around but nothing really to bump into, and with no more stars it's very cold and dark."