Enormous Bubble Eight-Billion Light-years Across Surrounds our Galactic Neighborhood

Astronomers using NASA's Hubble Space Telescope have ruled out an alternate theory on the nature of dark energy after recalculating the expansion rate of the universe to unprecedented accuracy nixing the theory that an enormous bubble of relatively empty space eight billion light-years across surrounds our galactic neighborhood. If we lived near the center of this void, observations of galaxies being pushed away from each other at accelerating speeds would be an illusion.
Led by Adam Riess of the Space Telescope Science Institute (STScI) and Johns Hopkins University, the Hubble observations were conducted by the SHOES (Supernova Ho for the Equation of State) team that works to refine the accuracy of the Hubble constant to a precision that allows for a better characterization of dark energy's behavior.

The observations helped determine a figure for the universe's current expansion rate to an uncertainty of just 3.3 percent. The new measurement reduces the error margin by 30 percent over Hubble's previous best measurement of 2009.

The value for the expansion rate is 73.8 kilometers per second per megaparsec. It means that for every additional million parsecs (3.26 million light-years) a galaxy is from Earth, the galaxy appears to be traveling 73.8 kilometers per second faster away from us.

Every decrease in uncertainty of the universe's expansion rate helps solidify our understanding of its cosmic ingredients. Knowing the precise value of the universe's expansion rate further restricts the range of dark energy's strength and helps astronomers tighten up their estimates of other cosmic properties, including the universe's shape and its component of neutrinos, or ghostly particles, that filled the early universe.

"We are using the new camera on Hubble like a policeman's radar gun to catch the universe speeding," Riess said. "It looks more like it's dark energy that's pressing on the gas pedal."

Dark energy is one of the greatest cosmological mysteries in modern physics. Even Albert Einstein conceived of a repulsive force, called the cosmological constant, which would counter gravity and keep the universe stable. He abandoned the idea when astronomer Edwin Hubble discovered in 1929 that the universe is expanding. Observational evidence for dark energy didn't come along until 1998, when two teams of researchers (one led by Riess) discovered it.

This image at bottom of page shows the location of Cepheid variables found in the spiral galaxy NGC 5584. Ultraviolet, visible, and infrared data taken with Hubble's Wide Field Camera 3 in 2010 reveals Cepheids of varying periods. Those stars with periods of less than 30 days and between 30 and 60 days are marked with blue and green circles, respectively. A small number of Cepheids, with periods larger than 60 days, are marked in red.

The idea of dark energy was so far-fetched, many scientists began contemplating other strange interpretations, including the cosmic bubble theory.

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