Ask a Scientist: Black hole shapes
Black holes - cosmic vacuum cleaners that even light cannot escape - are a common feature in science fiction.
Whether you watched Spock's Planet Vulcan being sucked into a black hole in the latest Star Trek film or sat down through Disney's The Black Hole as a child, one thing is for sure, its power and mystery are fascinating.
But how accurate are science fiction movies?
When Stuff launched its "Ask a Scientist" series this week and invited readers to send in their questions, one reader wanted to know whether back holes were in fact round as portrayed in some movies.
We asked Canterbury's physics and astronomy professor Dr Ishwaree Neupane.
"This is probably one of the most abstract questions," he said.
The quick and simple answer is that a black hole is round, or oval if rotating.
However, it's more complicated than that.
The human eye can only see and interpret objects that are either zero-dimensional (a point-like object), one-dimensional (a long wire), two-dimensional (like a bicycle tube or donut) or three-dimensional (virtually like anything that you see around, birds, car, planets).
People could not interpret correctly if an object was four-dimensional - which includes the notion of time - unless one takes a 3D projection of the object on a screen.
Therefore, a four-dimensional black hole may appear as a three-dimensional ball or spherically symmetric object.
When you look at a black hole through other theories of gravity, however, such as string theory - which unite the laws of quantum mechanism with Einstein's theory of general relativity, and operates with 10 dimensions - it could look like rings, helices or even like the plant Saturn.
"Black holes, in general, can come in a myriad of shapes and sizes if one believes that the nature admits more than three space-like directions," Neupane said.
"Unfortunately there is no way to prove or disprove this assertion due to experimental limitations and also due to the fact that astrophysicists cannot actually investigate the shape of a black hole."
Neupane said as a result, a black hole could not be characterised by one particular shape.
"A black hole evaporates like an ordinary black body and its surface area is constantly changing, which means its shape is also changing."
The shape of a black hole was determined by three parameters - its total mass, total angular momentum and charges (electric, magnetic or scalar charges), he said.
Black holes were generally formed when massive stars that reached the end of their burning cycles expelled the outer layers of their atmosphere in a violent supernova explosion.
"The remaining core then collapses on itself, due to massive gravitational attractions pulling inward, and forms a space-like singularity with an incredibly massive centre," Neupane said.
"The gravitational pull that it exerts on surrounding matter is so strong that it forms an accretion disk around itself, and then begins to pull on normal matter from its surroundings."
Neupane said even photons, which were the fastest-travelling particles in the Universe, could not escape its pull and fell through the event horizon - also known as the point of no return.
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- © Fairfax NZ News
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