Explaining the accelerating expansion of the universe without dark energy
Enigmatic 'dark energy', thought to make up 68% of the universe, may not exist at all, according to a Hungarian-American team. The researchers believe that standard models of the universe fail to take account of its changing structure, but that once this is done the need for dark energy disappears. The team publish their results in a paper in Monthly Notices of the Royal Astronomical Society.
They gobble stars, bend space, warp time and may even provide gateways to other universes.
Black holes fire the imagination of scientists and science-fiction aficionados alike. But at least one thing about them wasn’t all that mind-bending: we’ve long understood black holes to be the end point in the life of a big star, when it runs out of fuel and collapses on itself.
However, in recent times astronomers have been confronted with a paradox: gigantic black holes that existed when the universe was less than a billion years old.
Since average-sized black holes take many billions of years to form, astrophysicists have been scratching their heads to figure out how these monsters could have arisen so early. It now seems that rather than being the end game in the evolution of stars and galaxies, supermassive black holes were around at their beginnings and played a major role in shaping them.
It was the little known English clergyman and scientist John Michell who, in 1783, first articulated the idea of “dark stars” whose gravity was so great they would prevent light from escaping them. The concept was astonishingly prescient even if parts of his theory – particularly those based on Newton’s idea that light particles had mass – were flawed.
The first accurate description of black holes came in 1916 from German physicist and astronomer Karl Schwarzschild. Schwarzschild was serving in the German Army at the time, despite already being over 40 years of age.
After seeing action on both the western and eastern fronts, Schwarzschild was sent home due to a serious auto-immune skin disease, pemphigus.
It was late 1915 and Einstein’s theory of General Relativity had just been published. Inspired, Schwarzschild lost no time writing a paper that predicted the existence of black holes; it was published just months before he succumbed to his disease in May 1916.
According to Einstein’s theory, the force of gravity was the result of a mass distorting the fabric of space-time. In the same way that a bowling ball dimples the fabric of a trampoline, a star’s mass dimpled the space-time fabric of its system, keeping planets circling around it.
The theory was underpinned by equations laying out the interaction of energy, mass, space and time. Schwarzschild’s achievement was to apply Einstein’s equations to a simplified scenario: a perfectly spherical star. One of the things that jumped out of his mathematical musings was an object with such a strong gravitational pull that not even light could escape it.
While Schwarzschild’s idea made sense in the theoretical realm of mathematics, most physicists did not expect to find an exemplar in the real universe.
