Curiosities about black holes. What would happen if we fell into a black hole? What lies beyond the event horizon? How are they detected? Black holes are fascinating cosmic objects that, in turn, raise many questions.
Black holes form a group of cosmic objects that are among the most mysterious in the universe. Scientists have been theorizing about their existence for a hundred years. Some indirect evidence of Black holes existence has already been discovered. We obtained the first image of one of them in early 2019.
The details of the structure of a black hole were calculated using Albert Einstein’s theory of general relativity. Singularity forms the center of a black hole and is hidden by the “surface” of the object, the event horizon. Within the event horizon, the escape velocity (i.e., the speed required for matter to escape the gravitational field of a cosmic object) exceeds the speed of light, so even light rays cannot escape.
Video: Facts About Black Holes
Only the most massive stars, which are at least three times the size of our Sun, become black holes at the end of their lives. Stars with a lower mass, like our own, evolve into other bodies, like white dwarfs or neutron stars.
Two studies (in Physical Review Letters and Astrophysical Journal Letters) describing the discovery of the most massive black hole ever detected with gravitational waves were published Sept. 2, 2020. The research team discovered the merger of two black holes, one of which was much more massive than any other observed in such a collision. The researchers believe that the heavier of the two holes may be the result of an earlier merger between two black holes.
Black holes are fascinating objects that themselves raise many questions. In this article, we take a closer look at what we know about black holes.
Nothing can escape the Singularity
As we noted in the introduction. A black hole occurs when a dying star, which has completely exhausted its fuel, collapses until its gravitational field becomes so powerful that neither matter nor light can escape.
The result is a black hole, a singularity or point of zero volume and infinite density hidden behind an event horizon.
They may have non-stellar origins
We have already mentioned that black holes are formed when a massive star collapses. But some black holes apparently have a non-stellar origin. Several astronomers have speculated that large amounts of interstellar gas accumulate at the centers of quasars and galaxies and collapse to form supermassive black holes.
It is estimated that a mass of gas falling rapidly into a black hole releases more than 100 times as much energy as the same amount of mass through nuclear fusion. Consequently, the collapse of millions or billions of solar masses of interstellar gas under the gravitational pull of a large black hole would explain the enormous energy output of quasars and certain galactic systems.
The closest black hole
Sagittarius A*, the black hole at the center of our galaxy, is about 26 000 light-years away. But the nearest black hole is in the triple star system LB-1. It is ‘only’ 1000 light-years from Earth in the constellation Telescopium. It has a mass at least four times that of the Sun and is about 25 to 30 kilometers in diameter.
Size is determined by the radius of their event horizon
The radius of the event horizon is called the Schwarzschild radius, after the German astronomer Karl Schwarzschild, who in 1916 predicted the existence of collapsed stellar bodies that do not emit radiation. The size of the Schwarzschild radius is proportional to the mass of the collapsing star. For a black hole with a mass 10 times that of the Sun, the radius would be 30 km.
The most massive black hole
TON 618 is the largest black hole in the known universe. It has a luminosity equivalent to that of 140 trillion of our suns. TON 618 has an extremely high gravitational pull. TON 618 may have been formed by the merger of several black holes in the past.
Often discovered by fluctuations in their gravitational fields
Black holes cannot be observed directly because of their small size and the fact that they do not emit light. However, they can be “observed” indirectly through the effects of their enormous gravitational fields on nearby matter.
For example, when a black hole is part of a binary star system, the matter flowing in from its companion is strongly heated and then emits X-rays before entering the black hole’s event horizon and disappearing forever.
The first photo of a black hole
The first (and only) direct detection of a black hole was made on April 10, 2019. The image you see is a “snapshot” of the black hole at the center of the massive galaxy M87. M87 is about 55 million light-years from Earth. You can see the image as captured by the Event Horizon Telescope (EHT). This black hole is 6.5 billion times more massive than the Sun.
This image was the first direct visual evidence of a supermassive black hole and its shadow. The ring is brighter on one side because the black hole is spinning. The spin of the material on the side of the black hole has its emission affected by the Doppler effect. The shadow of the black hole is about five and a half times the size of the event horizon. Which marks the boundary of the black hole where the escape velocity is equal to the speed of light.
Black holes may not be so black after all
In 1974, Stephen Hawking wrote that:
- Black holes are not really “that black” due to the effects of quantum physics
- There is something that can “escape” from black holes: Radiation
This explanation is included in his theory of Hawking radiation. Hawking’s theory was never awarded the Nobel Prize in Physics because it could not be proven. Disadvantages of the activity of a theoretical physicist :).
What would happen if you fell into a black hole?
No one can say for sure what would happen, but physically we would be sucked into a kind of “bottomless pit.” If a human could reach the event horizon of a black hole and pass through it, he or she would probably undergo what is called spaghettification.
As we approach the black hole, the force of gravity at the head would not be the same as at the feet, so (as the term implies) our bodies would tend to stretch and probably break apart.
What lies beyond a black hole?
We cannot be sure. Beyond a black hole, the laws of physics are deformed, and time could not exist either. Bodies crossing the event horizon, or a beam of light directed at such an object, would seemingly simply disappear.
Many scientists are making the connection between singularities and the Big Bang theory, which proposes that our universe exploded from what might have been a singularity. Connecting with the multiverse theory, this hypothesis suggests that a black hole would be an ‘exit door’ from our universe, to give rise to another universe, through what we know as white holes.
But all this is nothing more than assumptions, for now.