Will it compress into some new state, such as the quarks that are thought to be the building blocks of neutrons, or some even more fundamental building block? We just don’t know.
What exactly happens when so much mass is concentrated in the same place is not understood. So, the density of a neutron star would be sufficient to form a black hole if the object had about 2,500 times the mass of the sun. DensityĬuriously, the density needed to form a black hole scales as the inverse square of the total mass. Yet even a neutron star is not dense enough, by a about a factor of 50, to form a black hole of the sun’s mass. The densest form of matter so far observed in nature is that encountered in so-called neutron stars, an entire star composed only of neutrons. Animated simulation of gravitational lensing caused by a black hole going past a background galaxy. That’s more extreme than the density of an atomic nucleus. The matter density needed to form such a black hole is extremely high – about 2 x 10 19 kg per cubic metre. The boundary between light paths that just manage to pass a density concentration and those that do not is called the “event horizon” – the greater the mass of a density concentration, the larger the size of this “surface of no return”.įor an object as massive as our sun, the event horizon is about 6km in diameter. If the dimple becomes too deep, light that passes sufficiently close will be deflected into a spiral path that ends on the marble and it will not escape at all. Passing light can be thought of as confined to the rubber sheet and when it passes near a marble it will be deflected from its original path by passing through the dimple. The gravitationally lensed image of a background blue galaxy seen almost exactly behind a foreground red galaxy. After all, why should the mass-less particles of light, photons, feel the influence of any mass they pass? The surprising answer is that the basic shape of our universe is influenced by each mass within it, like the dimples in a rubber sheet caused by an occasional marble. That prediction has been spectacularly confirmed in recent years by the discovery of “gravitational lenses” – where a background source and a foreground mass are so closely aligned that the light from the background source is highly distorted, even to the point of forming an almost complete arc around the foreground mass.īefore 1916, we had not considered that this might be possible. The reason this question even arose dates back to Einstein’s prediction of 1916, in his Foundations of General Relativity, that the direction light travels will be bent in the direction of any nearby mass. It’s the answer to the question: “What happens if the density of matter in a region becomes so high that not even light can escape?” The concept of a “black hole” is one of the most curious in astrophysics.
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