Improved Hubble Yardstick Gives Fresh Evidence for New Physics in the Universe NASA | STScI | JHU | HubbleSite | 2018 Feb 22
This illustration shows three steps astronomers used to measure the
universe's expansion rate (Hubble constant) to an unprecedented accuracy,
reducing the total uncertainty to 2.3 percent. The measurements streamline
and strengthen the construction of the cosmic distance ladder, which is used
to measure accurate distances to galaxies near to and far from Earth. The
latest Hubble study extends the number of Cepheid variable stars analyzed to
distances of up to 10 times farther across our galaxy than previous results. Credits: NASA, ESA, A. Feild (STScI), and A. Riess (STScI/JHU)
Astronomers have used NASA's Hubble Space Telescope to make the most precise measurements of the expansion rate of the universe since it was first calculated nearly a century ago. Intriguingly, the results are forcing astronomers to consider that they may be seeing evidence of something unexpected at work in the universe.
That's because the latest Hubble finding confirms a nagging discrepancy showing the universe to be expanding faster now than was expected from its trajectory seen shortly after the big bang. Researchers suggest that there may be new physics to explain the inconsistency. ...
Planck's result predicted that the Hubble constant value should now be 67 kilometers per second per megaparsec (3.3 million light-years), and could be no higher than 69 kilometers per second per megaparsec. This means that for every 3.3 million light-years farther away a galaxy is from us, it is moving 67 kilometers per second faster. But Riess's team measured a value of 73 kilometers per second per megaparsec, indicating galaxies are moving at a faster rate than implied by observations of the early universe.
The Hubble data are so precise that astronomers cannot dismiss the gap between the two results as errors in any single measurement or method. "Both results have been tested multiple ways, so barring a series of unrelated mistakes," Riess explained, "it is increasingly likely that this is not a bug but a feature of the universe." ...
New Parallaxes of Galactic Cepheids from Spatially Scanning the Hubble
Space Telescope: Implications for the Hubble Constant - Adam G. Riess et al
Hubble Space Telescope (2018-02-22)
: 73.45±1.66 (km/s)/Mpc
<<Parallax measurements of galactic cepheids; the value suggests a discrepancy with CMB measurements at the 3.7σ level. The uncertainty is expected to be reduced to below 1% with the final release of the Gaia catalog.>>
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Most precise measurement yet adds to debate over universe’s expansion rate
Image Credit: NASA, ESA, and A. Feild (STScI)
Science Credit: NASA, ESA, and A. Riess (STScI/JHU)
Using the power and synergy of two space telescopes, astronomers have made the most precise measurement to date of the universe’s expansion rate.
The results further fuel the mismatch between measurements for the expansion rate of the nearby universe, and those of the distant, primeval universe — before stars and galaxies even existed.
This so-called “tension” implies that there could be new physics underlying the foundations of the universe. Possibilities include the interaction strength of dark matter, dark energy being even more exotic than previously thought, or an unknown new particle in the tapestry of space.
Combining observations from NASA’s Hubble Space Telescope and the European Space Agency’s (ESA) Gaia space observatory, astronomers further refined the previous value for the Hubble constant, the rate at which the universe is expanding from the big bang 13.8 billion years ago.
But as the measurements have become more precise, the team’s determination of the Hubble constant has become more and more at odds with the measurements from another space observatory, ESA’s Planck mission, which is coming up with a different predicted value for the Hubble constant. ...
Milky Way Cepheid Standards for Measuring Cosmic Distances and
Application to Gaia DR2: Implications for the Hubble Constant - Adam G. Riess et al