by Photo: Contributed
On October 9, orbiting observatories detected the largest gamma-ray burst ever seen.
It was so strong that it affected our ionosphere. It 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 account for the power of the explosion when it reached us, the amount of energy involved in the production must have been unimaginably great. Gamma rays are the highest energy form of electromagnetic waves. To produce them, the release of energy had to be not only enormous, but also highly concentrated.
The most likely explanation is the birth of a black hole. This involved an aging star exploding, with its core undergoing incredibly extreme compression. One way to achieve this is by using a strong, gravitational compression, another is compression by strong shock waves created 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 compressed it to half its current diameter, we would find ourselves four times heavier. This is how we can enhance gravity by compressing a body into a smaller size. This contraction is hard to imagine in the case of our planet, but it is something that happens in stars.
Atoms consist of a nucleus containing a collection of protons and neutrons, surrounded by orbiting electrons. However, by far the main component of atoms is empty space. Although mostly nothing, atoms strongly resist compression. That is why we can walk on the ground without falling. However, if we push hard enough, individuals can be forced to shrink.
Stars form through the balance of two forces – gravity due to the material they are made of pulling inward and outward pressure maintained by the energy production in their cores.
When the fuel runs out and energy production slows and then stops, the outward pressure drops and the stars collapse under their own gravity. As shrinkage progresses, gravitational compression increases.
For stars like the Sun, the pressure becomes high enough to force its atoms to contract into their most compact form. Matter in this form is referred to as “degenerate”, or more correctly “quantum degenerate”. A teaspoonful of this material would weigh several tons.
Stars in this state are referred to as “white dwarfs”. When it becomes one, the Sun will shrink from a diameter of 1.5 million kilometers to about the diameter of Earth, about 13,000 kilometers.
More massive stars can exert much more compression when they collapse and will also undergo explosions that create inward-moving shock waves that compress their cores so hard that the atoms collapse completely, eliminating all that empty space, forming a mass of neutrons. This reduces the star to a few kilometers in diameter, with a teaspoon weighing about a billion tons.
If there is enough compression force, the story does not end there.
There is a limit where the increasing gravitational force as the star shrinks overcomes all resisting forces. As far as our current understanding goes, the contraction will continue indefinitely, although common sense says that’s not really likely.
As the star shrinks and its surface gravity increases, it reaches a point where the pressure this force exerts on the fabric of spacetime becomes excessive. A ‘bubble’ forms around it, called the ‘event horizon’, from which nothing, not even light, comes out, hence the term ‘black hole’.
As the star’s material disappears through this horizon, there is a huge explosion as most of that material is completely converted into energy. This is what we believe we witnessed.
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• In the early evening, Jupiter is in the southeast and Saturn in the southern sky. Mars rises later.
• The Moon will be full on November 8th.
This article was written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.
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