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Trending Science: Scientists announce that the universe is expanding much faster than previously thought

NASA and the European Space Agency (ESA) have announced that the universe is expanding 5 % to 9 % faster than previously thought, after using the Hubble space telescope to measure the distance to stars in 19 galaxies beyond the Milky Way.
Trending Science: Scientists announce that the universe is expanding much faster than previously thought
The rate of expansion did not match predictions based on measurements of radiation left over from the Big Bang that created the known universe around 13.8 billion years ago. Specifically, the new study observed the light signatures of around 2 400 Cepheid variable stars in 19 different galaxies, as well as those of 300 Type Ia supernovae. This is because Cepheids and Type Ia supernovae constitute part of the Cosmic Distance Ladder, an invaluable tool used by astronomers attempting to map the vast distances between galaxies.

Celestial objects that fall into this category boast a known quantity that can be measured with a high degree of accuracy. For example, we know how bright a Type Ia supernova will shine, and astronomers have also identified a strong relationship between a Cepheid star’s brightness and its pulsation period. The team then compared the observations of the study subjects with the stretching of light from receding galaxies, which astronomers use to mark the stretching of space, allowing the researchers to calculate the speed of universal expansion. This value is known as the Hubble constant.

Arriving at a new expansion rate of 73.2 kilometres (45.5 miles) per second per megaparsec, the latest figure represents a 76 % reduction in uncertainty regarding the Hubble constant since 2005, when the Supernova H0 for the Equation of State (SHOES) project began mapping the expansion of the universe. With a megaparsec being 3.26 million light years, the consequence of this adjustment is that the distance between cosmic objects will double in another 9.8 billion years time.

However, these speeds do not match previous predictions of the expansion rate from other observations made by NASA’s Wilkinson microwave anisotropy Probe, or the ESA’s Planck satellite. Both went into orbit to study the afterglow of the Big Bang, and both delivered lower and slightly different predictions for cosmic expansion, the first 5 % and the second 9 % lower.

‘You start at two ends, and you expect to meet in the middle if all of your drawings are right and your measurements are right,’ commented lead author of the research and Nobel Prize winner Adam Riess. ‘But now the ends are not quite meeting in the middle and we want to know why.’

The research team behind the joint NASA-ESA study believe that the culprit for the unexpected acceleration could be one of the invisible (due to not emitting any radiation or light) phenomena thought to comprise roughly 95 % of the Universe, known as dark matter, dark energy and dark radiation. These dark phenomena cannot be studied directly, and astronomers study them through the influence they have on visible matter, such as galaxies and superclusters.

It is possible that dark matter is responsible for the acceleration thanks to a characteristic that we are simply yet to discover due to our limited observational capabilities. The discrepancy could also mean that Albert Einstein's theory of relativity is incomplete when working with objects on a universal scale. Alternatively, dark energy could be pushing galaxies away from one another much more powerfully than previously thought. Finally, a family of subatomic particles that travel close to the speed of light, known as dark radiation, could have provided the extra energy to accelerate the early Universe.

One very long-term consequence for the accelerated expansion of the universe could be that in many billions of years time, all of the other galaxies will have receded beyond a ‘cosmic horizon’, leaving the Milky Way utterly alone in the visible universe.

However, back on Earth, the NASA-ESA research team now intends to use the next generation of ground and spacefaring telescopes such as the James Webb Space Telescope (JWST) and the ESO's European Extremely Large Telescope (E-ELT) to reduce the uncertainty in the Hubble constant to 1 % only.

Source: Based on media reports

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