If you search “black hole” on the internet, at least one of the top results will claim to tell you what could happen if a person fell into one.
But to save you a lot of time and fruitless reading, the short, honest, but perhaps least thrilling answer is that no one really knows. Don’t fret. Scientists have some well-founded, albeit mind-bending ideas about what might be going on. To understand them, though, you first need to grasp some basic concepts about black holes.
What are black hole and what makes them so weird?
Grab a small object, like a pencil, near you. Got it? Congratulations, you just won a battle against the entire gravitational pull of planet Earth. “The gravitational force, of all the forces of nature, is the weakest one,” says astronomer and NASA astrophysicist Roopesh Ojha.
Weak as it can be, gravity rules the entire universe. If you threw the pen you just grabbed into the air, it would come back down rather quickly. But there are places in the Universe where this pull is almost infinitely stronger than on Earth—so powerful that not even light can escape their grab: Meet black holes. These space objects extremely dense, where the gravitational force is so strong that absolutely nothing can resist its pull.
“As a child, this is how I understood black holes: They are objects whose gravity is so strong that if you get close enough, there is no rocket that can take you out,” Ojha says.
What happens if I get too close to a black hole?
Right now, the Earth is pulling a little bit harder on whichever part of your body is closer to the ground. You can’t feel or see the effects of that pull, called tidal force, because, relative to the size of the universe, the Earth isn’t all that big. So, the force of gravity in return isn’t all that strong.
But since black holes are much more massive, the tidal force there is much stronger than on Earth. “If you are an astronaut falling towards a black hole feet first”, explains Ojha, “ the pull on your feet is so much stronger than the pull in your head, so in the direction that you are falling, you get stretched [by the tidal forces].” The very real astrophysics term for this process is pretty straightforward: spaghettification….
By: Maria Paula Rubiano
A black hole is a region of spacetime where gravity is so strong that nothing, including light or other electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. Although it has a great effect on the fate and circumstances of an object crossing it, it has no locally detectable features according to general relativity.
In many ways, a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly.
Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. In 1916, Karl Schwarzschild found the first modern solution of general relativity that would characterize a black hole. David Finkelstein, in 1958, first published the interpretation of “black hole” as a region of space from which nothing can escape.
Black holes were long considered a mathematical curiosity; it was not until the 1960s that theoretical work showed they were a generic prediction of general relativity. The discovery of neutron stars by Jocelyn Bell Burnell in 1967 sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality. The first black hole known was Cygnus X-1, identified by several researchers independently in 1971.
Black holes of stellar mass form when massive stars collapse at the end of their life cycle. After a black hole has formed, it can grow by absorbing mass from its surroundings. Supermassive black holes of millions of solar masses (M☉) may form by absorbing other stars and merging with other black holes. There is consensus that supermassive black holes exist in the centres of most galaxies.
The presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Any matter that falls onto a black hole can form an external accretion disk heated by friction, forming quasars, some of the brightest objects in the universe. Stars passing too close to a supermassive black hole can be shredded into streamers that shine very brightly before being “swallowed.”
If other stars are orbiting a black hole, their orbits can be used to determine the black hole’s mass and location. Such observations can be used to exclude possible alternatives such as neutron stars. In this way, astronomers have identified numerous stellar black hole candidates in binary systems and established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses.
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