The Universe Is Expanding Faster Than We Thought
Dark energy may be even weirder than thought, or perhaps Einstein's theory of gravity needs to be tweaked.
Less than 20 years after the startling discovery that the expansion of the universe is accelerating -- a finding that led to a Nobel Prize in Physics for two teams of astronomers -- comes a potentially more jarring revelation that the cosmos is busting out in all directions even faster than predicted.
Nobel laureate Adam Riess, with the Space Telescope Science Institute in Baltimore, and colleagues made the discovery after creating a more advanced and accurate cosmic yardstick which enabled them recalculate the distances of 19 galaxies.
The astronomers used the Hubble Space Telescope to look at galaxies that have a type of star known as a Cepheid variable, as well as a particular type of supernova. Both objects radiate predictable amounts of light.
They then compared the stars' relative brightness (which is similar to figuring out how far away a 100-watt light bulb is based on how bright or dim it appears) with the expansion of space as determined by the stretching of light from receding galaxies.
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The astronomers came up with a new rate of expansion for the universe over time (the so-called Hubble constant) that is five- to nine percent faster than current predictions.
The new number means that the distance between cosmic objects will double in another 9.8 billion years, the Space Telescope Science Institute noted in a press release.
The discovery raises an immediate issue since the number does not jive with the expansion rate derived from analysis of the cosmic microwave background radiation, the remnant rays from the Big Bang explosion 13.8 billion years ago.
Measurements of the afterglow from the Big Bang by NASA's Wilkinson Microwave Anisotropy Probe and the European Space Agency's Planck satellite mission yield predictions for the Hubble constant that are 5 percent and 9 percent, respectively, smaller than Riess and colleagues' calculation, the Space Telescope Science Institute said.
"If we know the initial amounts of stuff in the universe, such as dark energy and dark matter, and we have the physics correct, then you can go from a measurement at the time shortly after the Big Bang and use that understanding to predict how fast the universe should be expanding today," Riess said.
"However, if this discrepancy holds up, it appears we may not have the right understanding, and it changes how big the Hubble constant should be today," he added.
Scientists have a few ideas for what is causing the discrepancy, including that a more powerful or growing dark energy force is pushing the galaxies apart faster than predicted, or imbuing dark matter with some weird, unexpected characteristics.
"We know so little about the dark parts of the universe, it's important to measure how they push and pull on space over cosmic history," said astronomer Lucas Macri, with Texas A&M University in College Station.
Another theory is that unknown subatomic particles, similar to neutrinos, could be throwing off the calculations.
Finally, a speedier universe also may mean that Einstein's theory of gravity is incomplete.
The research will be published in an upcoming issue of The Astrophysical Journal.