Picture: Contributed
On October 9, orbiting observatories detected the largest gamma-ray burst we have ever seen.
It was so strong it affected our ionosphere. He came from beyond the stars of the constellation Sagitta (“The Arrow”). The gamma rays came from an object about 2.4 billion light-years away.
To explain the force of the explosion when it hit us, the amount of energy involved in the production must have been incredibly large. Gamma rays are the most energetic form of electromagnetic waves. To produce them, the release of energy not only had to be enormous, but also very concentrated.
The most likely explanation is the birth of a black hole. It involved the explosion of an aging star, its core undergoing incredibly extreme compression. One way to achieve this is by using intense gravitational compression, another is compression by strong shock waves generated by an explosion.
The gravity at the surface of a body depends on two things: its mass and its diameter. For example, if we kept the mass of our world as it is and somehow squeezed it down to half its current diameter, we would end up four times heavier. So we can increase gravity by compressing a body to a smaller size. This shrinkage is hard to imagine in the case of our planet, but it is something that happens to stars.
Atoms are made up of a nucleus containing a collection of protons and neutrons, surrounded by orbiting electrons. However, by far the main ingredient of atoms is empty space. Although they are mostly nothing, atoms strongly resist compression. This is why we can walk on the ground without falling through. However, if we press hard enough, the atoms can be forced to shrink.
Stars form through the balance of two forces – gravity due to the material they are made of pulling in and out the pressure maintained by the energy production in their core.
When the fuel runs out and energy production slows and then ceases, the external pressure drops and the stars collapse under their own gravity. As the shrinkage progresses, the gravitational compression increases.
For stars like the Sun, the pressure becomes high enough to force its atoms to shrink into their most compact form. Matter in this form is called “degenerate”, or more properly “quantum degenerate”. A teaspoonful of this material would weigh a few tons.
Stars in this state are called “white dwarfs”. When it becomes one, the Sun will go from a diameter of 1.5 million kilometers to about the diameter of the Earth, or about 13,000 km.
More massive stars can impose much greater compression when they collapse, and will also experience explosions generating inward-moving shock waves that compress their cores so hard that the atoms completely collapse, eliminating all that empty space, forming a mass of neutrons. This brings the star down to just a few kilometers across, with a teaspoon weighing around a billion tons.
If enough compressive force is available, the story doesn’t end there.
There is a threshold where the increase in gravitational pull as the star gets smaller overcomes all resistance forces. As far as our current understanding is concerned, shrinkage will continue indefinitely, although common sense says that’s not really likely.
As the star becomes smaller and its surface gravity increases, a point is reached where the strain this force places on the fabric of spacetime becomes too great. A “bubble” forms around it, called the “event horizon”, from which nothing comes out, not even light, hence the term “black hole”.
As the material from the star disappears through this horizon, there is a huge explosion as most of this material is completely transformed into energy. This is what we believe we witnessed.
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• In the early evening, Jupiter is in the southeast and Saturn is in the southern sky. Mars rises later.
• The Moon will be full on November 8th.
This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.
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