Arthur J. Villasanta – Fourth Estate Contributor
Baltimore, MD, United States (4E) – An international team of astronomers called the Supernova H0 for the Equation of State (SH0ES) has announced the most precise measurements of the expansion rate of the Universe to date.
SH0ES has been on a quest to refine the accuracy of the Hubble Constant since 2005. It includes members from the Johns Hopkins University; the American Museum of Natural History; the Neils Bohr Institute; the National Optical Astronomy Observatory, and many prestigious universities and research institutions. The team is led by Adam Reiss of the Space Telescope Science Institute (STScI).
For their study, and consistent with their long term goals, the team sought to construct a new and more accurate “distance ladder” compared to the Hubble Constant.
The Hubble Constant is derived by relying on distance markers like Cepheid variables, which are pulsating stars whose distances can be inferred by comparing their intrinsic brightness with their apparent brightness. These measurements are then compared to the way light from distant galaxies is redshifted to determine how fast the space between galaxies is expanding.
To build their new distance ladder, the team conducted parallax measurements using Hubble’s Wide Field Camera 3 (WFC3) of eight newly-analyzed Cepheid variable stars in the Milky Way. These stars are about 10 times farther away than any studied previously, or between 6,000 and 12,000 light-year from Earth. They also pulsate at longer intervals.
The team also developed a new method where Hubble would measure a star’s position a thousand times a minute every six months for four years to ensure accuracy that would account for the wobbles of these stars. The team then compared the brightness of these eight stars with more distant Cepheids to ensure that they could calculate the distances to other galaxies with more precision
Using the new technique, Hubble was able to capture the change in position of these stars relative to others, which simplified things immensely.
“This method allows for repeated opportunities to measure the extremely tiny displacements due to parallax,” said Riess. “You’re measuring the separation between two stars, not just in one place on the camera, but over and over thousands of times, reducing the errors in measurement.”
Compared to previous surveys, the team was able to extend the number of stars analyzed to distances up to 10 times farther. Their results, however, contradicted those obtained by the European Space Agency’s (ESA) Planck satellite, which has been measuring the Cosmic Microwave Background (CMB), or the leftover radiation created by the Big Bang, since it was deployed in 2009.
By mapping the CMB, Planck has been able to trace the expansion of the cosmos during the early Universe from 378,000 years after the Big Bang. 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
Based on their survey, however, Riess’s team obtained a value of 73 kilometers per second per megaparsec, a discrepancy of 9%. Essentially, their results indicate that galaxies are moving at a faster rate than that implied by observations of the early Universe.
Because the Hubble data was so precise, astronomers cannot dismiss the gap between the two results as errors in any single measurement or method.
“The community is really grappling with understanding the meaning of this discrepancy… Both results have been tested multiple ways, so barring a series of unrelated mistakes. it is increasingly likely that this is not a bug but a feature of the universe,” said Riess.
These latest results, therefore, suggest that some previously unknown force or some new physics might be at work in the Universe. They suggest Dark Energy could be pushing galaxies apart with increasing strength.
Another possibility is that there is an undiscovered subatomic particle out there similar to a neutrino, but interacts with normal matter by gravity instead of subatomic forces. These “sterile neutrinos” would travel at close to the speed of light and could collectively be known as “dark radiation.”
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