Of all the strange objects that exist in the Universe, black holes are without doubt the strangest. Before 1971, black holes were believed to be purely theoretical phenomena, but this perception was radically altered after astronomers detected Cygnus X-1, the first physical black hole ever discovered.
Nevertheless, their mystique has only continued to grow over the decades, and today black holes hold an almost science-fiction level of fascination. With that said, let’s dive right in a explore 10 awesome black hole facts that are sure to blow your mind.
Top 10 Black Hole Facts
- Caused by a massive star collapsing in upon itself
- Black hole singularities are zero-dimensional
- Black holes distort space and slow time
- Objects appear to slow down near a black hole
- Objects falling into a black hole are spaghettified
- Black hole gravity equal to other same mass objects
- Wormholes appear similar to black holes
- Theory of black holes proposed in 1783
- Black holes eventually evaporate over time
- The closest black hole is 1,600 light-years away
A massive star collapsing in upon itself – A black hole is formed when a large star starts running out of fuel and begins to collapse under its own gravity. Such a star may become a white dwarf or a neutron star, but if the star is sufficiently massive then it may continue shrinking eventually to the size of a tiny atom, known as a gravitational singularity. A black hole refers to the region in space in which the singularity’s gravitational force is so strong that not even light can escape its pull.
Black hole singularities are zero-dimensional – The singularity at the core of a black hole may shrink to a size smaller than an atom, with its gravitational force so strong that it forces the spacetime surrounding it to be bent to infinite curvature. How small is a gravitational singularity? While it is said to be a point of zero dimensions, our current physical theories suggest that the smallest known scale for space-time is a Planck length, beyond which our physical theories break down and don’t make sense. As American theoretical physicist Kip Thorne states in his description of a singularity, it is a “point where all laws of physics break down.”
Black holes distort space-time and slow time – The mass of a black hole is so dense and the gravity of its singularity so strong that, in accordance with Einstein’s Theory of General Relativity, it actually distorts the space-time around it and not even light can escape. The boundary beyond which light cannot escape the black hole’s gravity well is known as the event horizon, while its radius is called the Schwarzschild radius (see picture below for details). Once particles and light rays go past the event horizon their light cones “tip over” and point to the singularity, which now represents all future-directed paths with no escape possible.
Interestingly, by keeping a safe distance from a black hole’s event horizon, a spaceship would experience a slower passage of time compared to the rest of the universe. A spacecraft could therefore travel centuries into the future relative to Earth, although just a few hours would seem to have passed for those people onboard the craft.
Objects appear to slow down near a black hole – To an outside observer with a telescope, an object passing the event horizon will appear to slow down then “freeze” in time without ever seeming to pass through the event horizon. This is because the light takes longer to escape the black hole’s gravitational pull and light signals won’t reach the viewer for an infinitely long time.
As time elapses, the light subsequently becomes red-shifted and dimmer as its wavelength becomes longer, eventually disappearing from the sight of the observer as it becomes infrared radiation, then radio waves.
A person falling into a black hole would be spaghettified – If a person was able to survive long enough to describe falling into a black hole, he would at first experience weightlessness as he goes into free fall, but then feel intense “tidal” gravitational forces as he got closer to the center of the black hole. If his feet were closer to the center than his head, then his feet would feel a stronger pull until he eventually is stretched and then ripped apart. As he falls in he may observe distorted images as the light bends around him and he will also still be able to see beyond the black hole as light continues to reach him from the outside.
Gravitational pull same as other objects of the same mass – It is important to realize that a black hole’s gravitational field is the same as that of any other object in space of the same mass. In other words, it won’t “suck” objects in any more than any other normal star, with things being more likely to just fall into them if they got too close to their event horizon. If our Sun was replaced with a black hole of equal mass, for example, the Earth would continue experiencing the same gravitational force as before. Only when objects get too close to the black hole would the stronger gravitational force become apparent.
Wormholes appear similar to black holes – A traversable wormhole, known alternatively as a Lorentzian wormhole, Schwarzschild wormhole or Einstein-Rosen bridge, is a theoretical opening in space-time allowing a “shortcut” through intervening space to another location in the Universe. However, from the outside wormholes may exhibit many of the characteristics usually associated with a black hole and be virtually impossible to tell apart.
In recent times, theoretical physicists, such as Kip Thorne, have speculated that wormholes and quantum entanglement may in fact be the very same phenomenon. In other words, entangled particles may be connected by an Einstein-Rosen bridge. If this proves correct, it would represent a huge stride towards a Unified Field Theory and trying to unify the fields of quantum mechanics and gravity.
John Mitchell developed the theory of black holes in 1783 – John Michell (1783) and Pierre-Simon Laplace (1796) were the first people to propose the concept of “dark stars” or objects which, if compressed into a small enough radius, would have an escape velocity which exceeded even the speed of light. Later, the term “frozen star” was used to describe the last phase of a star’s gravitational collapse, when light unable to escape from its surface would make the star appear frozen in time to an observer. In the 20th century, John Wheeler eventually coined the phrase “black hole” as the object would absorb all the light that hits it while reflecting nothing back.
Black holes eventually evaporate over time – Physicists now believe that black holes actually radiate small numbers of mainly photon particles and so can lose mass, shrink, and ultimately vanish over time. This unverified evaporation process is known as “Hawking Radiation”, after Professor Stephen Hawking who theorized about its existence in 1974. However, it is a staggeringly slow process and only the smallest black holes would have had time to evaporate significantly during the 14 billion years the Universe has existed.
Closest black hole star is just 1,600 light-years away – It is now thought that most galaxies are held together by supermassive black holes at their centers, which cluster hundreds of solar systems around them. In fact, 25,640 light years away at the center of our own Milky Way galaxy is a black hole called Sagittarius A or Sgr A that has 30 million times the mass of our own sun. This is not the nearest black hole to Earth, though. That honor belongs to a recently discovered black hole called Gaia BH1 located in the constellation of Ophiuchus.