Post by Andrei Tchentchik on Jun 26, 2019 18:48:00 GMT 2
(.#230).- What is inside a black hole??
By Tristan Vey - Updated 16/04/2019 at 10:58
If the existence of black holes is no longer any doubt, that does not mean that we fully understand these objects. What is happening in their hearts is still the subject of much speculation.
Last week, astronomers from around the world, gathered in the Event Horizon Telescope collaboration, unveiled the first ever portrait of a black hole (dubbed "Pōwehi"), a historic first that we have come a long way back in. Figaro: But it is a question that many well-informed readers have asked themselves, and to which we have not replied: what exactly is inside these strange objects?
This is a question all the more legitimate that ... nobody really knows. "Even from the mathematical point of view, we do not know in detail what happens," warns the theoretical physicist Thibaut Damour, permanent professor at the Institute of Advanced Scientific Studies (IHES). "To put it another way, we still do not know how to calculate what's inside a black hole."
Let's start by recalling what we are talking about exactly. When Albert Einstein published his theory of general relativity in 1915, a German astrophysicist, Karl Schwartzschild, enjoyed the following weeks in solving the equations during his spare time as an artilleryman. German army on the Russian front.
Spatio-temporal torn fabric
In particular, he wonders if there are objects whose gravitational attraction would be so important that no object could escape it, not even the fastest in the universe, photons, these grains of light. He discovers that sufficiently concentrated masses meet these conditions, defining an area from which nothing can escape even the light. If we were next door, we would see only a sphere of absolute blackness. Hence this name of "black hole".
But what's going on inside this sphere? "If we could cross the horizon of a black hole, we probably would not really change by looking behind us," says Thibaut Damour. "The photons pass through this border easily. What they can not do is come out. "
It is harder to imagine what you would see by looking inward. In general relativity, space and time are two sides of the same coin. "In a black hole, the space-time fabric is broken," says the physicist. "On the face of it, what we find inside the horizon is a very big space but whose life is very limited. And the time you have left is proportional to the size of the black hole. "
An inverted Big Bang
If it is a supermassive black hole, like the one that has just been the subject of this great campaign of observations, then you will have a little more than a day before the time stops and that all the atoms that compose you are shredded to form a soup of the most elementary particles possible. If you are in a black hole whose mass is close to that of our Sun, you will only have a thousandth of a second in front of you (but you would have been torn by the tidal forces anyway before you even crossed the horizon). "We can then see the black hole as a sort of inverted Big Bang, a" Big Crunch, "says Thibaut Damour. "Instead of seeing the appearance of time and the dilation of space, you are witnessing a contraction of space and the disappearance of time."
If a black hole is a tear, is it permanent? "We do not really know," says the researcher. "Stephen Hawking has shown that it is possible for black holes to evaporate by emitting very light radiation. If they lose their mass, they could disappear. It would take a lot of time, but it would mean that the spatio-temporal tissue could finally heal. "That's a hypothesis. Some people think that the black hole could "bounce back" after reaching a concentration of mass limit in his heart. Still others think that the spatio-temporal tear could lead to a new universe. "These theories are more or less exotic," says Thibaut Damour. "The only truth is that we do not know anything about it right now."
F I N .
By Tristan Vey - Updated 16/04/2019 at 10:58
If the existence of black holes is no longer any doubt, that does not mean that we fully understand these objects. What is happening in their hearts is still the subject of much speculation.
Last week, astronomers from around the world, gathered in the Event Horizon Telescope collaboration, unveiled the first ever portrait of a black hole (dubbed "Pōwehi"), a historic first that we have come a long way back in. Figaro: But it is a question that many well-informed readers have asked themselves, and to which we have not replied: what exactly is inside these strange objects?
This is a question all the more legitimate that ... nobody really knows. "Even from the mathematical point of view, we do not know in detail what happens," warns the theoretical physicist Thibaut Damour, permanent professor at the Institute of Advanced Scientific Studies (IHES). "To put it another way, we still do not know how to calculate what's inside a black hole."
Let's start by recalling what we are talking about exactly. When Albert Einstein published his theory of general relativity in 1915, a German astrophysicist, Karl Schwartzschild, enjoyed the following weeks in solving the equations during his spare time as an artilleryman. German army on the Russian front.
Spatio-temporal torn fabric
In particular, he wonders if there are objects whose gravitational attraction would be so important that no object could escape it, not even the fastest in the universe, photons, these grains of light. He discovers that sufficiently concentrated masses meet these conditions, defining an area from which nothing can escape even the light. If we were next door, we would see only a sphere of absolute blackness. Hence this name of "black hole".
But what's going on inside this sphere? "If we could cross the horizon of a black hole, we probably would not really change by looking behind us," says Thibaut Damour. "The photons pass through this border easily. What they can not do is come out. "
It is harder to imagine what you would see by looking inward. In general relativity, space and time are two sides of the same coin. "In a black hole, the space-time fabric is broken," says the physicist. "On the face of it, what we find inside the horizon is a very big space but whose life is very limited. And the time you have left is proportional to the size of the black hole. "
An inverted Big Bang
If it is a supermassive black hole, like the one that has just been the subject of this great campaign of observations, then you will have a little more than a day before the time stops and that all the atoms that compose you are shredded to form a soup of the most elementary particles possible. If you are in a black hole whose mass is close to that of our Sun, you will only have a thousandth of a second in front of you (but you would have been torn by the tidal forces anyway before you even crossed the horizon). "We can then see the black hole as a sort of inverted Big Bang, a" Big Crunch, "says Thibaut Damour. "Instead of seeing the appearance of time and the dilation of space, you are witnessing a contraction of space and the disappearance of time."
If a black hole is a tear, is it permanent? "We do not really know," says the researcher. "Stephen Hawking has shown that it is possible for black holes to evaporate by emitting very light radiation. If they lose their mass, they could disappear. It would take a lot of time, but it would mean that the spatio-temporal tissue could finally heal. "That's a hypothesis. Some people think that the black hole could "bounce back" after reaching a concentration of mass limit in his heart. Still others think that the spatio-temporal tear could lead to a new universe. "These theories are more or less exotic," says Thibaut Damour. "The only truth is that we do not know anything about it right now."
F I N .
