Hubble Space Telescope Reveals New Estimate of Speed of Expansion of the Universe –“Hints at a New Physics”




The Hubble constant is crucial for modern astronomy as it can help to confirm or refute whether our picture of the Universe — composed of dark energy, dark matter and normal matter — is actually correct, or if we are missing something fundamental.

By using three galaxies as giant gravitational lenses, an international group of astronomers using the NASA/ESA Hubble Space Telescope have made an independent measurement of how fast the Universe is expanding. The newly measured expansion rate for the local Universe is consistent with earlier findings. These are, however, in intriguing disagreement with measurements of the early Universe. This hints at a fundamental problem at the very heart of our understanding of the cosmos. That discrepancy could hint at "new physics" beyond the standard model of cosmology.

The Hubble constant — the rate at which the Universe is expanding — is one of the fundamental quantities describing our Universe. A group of astronomers from the H0LiCOW collaboration, led by Sherry Suyu (associated with the Max Planck Institute for Astrophysics in Germany, the ASIAA in Taiwan and the Technical University) used the NASA/ESA Hubble Space Telescope and other telescopes in space and on the ground to observe five galaxies in order to arrive at an independent measurement of the Hubble constant.



The new measurement is completely independent of — but in agreement with — other measurements of the Hubble constant in the local Universe that used Cepheid variable stars and supernovae as points of reference heic1611. However, the value measured by Suyu and her team, as well as those measured using Cepheids and supernovae, are different from the measurement made by the ESA Planck satellite . But there is an important distinction — Planck measured the Hubble constant for the early Universe by observing the cosmic microwave background.

While the value for the Hubble constant determined by Planck fits with our current understanding of the cosmos, the values obtained by the different groups of astronomers for the local Universe are in disagreement with our accepted theoretical model of the Universe.

"The expansion rate of the Universe is now starting to be measured in different ways with such high precision that actual discrepancies may possibly point towards new physics beyond our current knowledge of the Universe," elaborates Suyu. "The Hubble constant is crucial for modern astronomy as it can help to confirm or refute whether our picture of the Universe — composed of dark energy, dark matter and normal matter — is actually correct, or if we are missing something fundamental," Suyu said.

Dark energy is a mysterious force which makes up about three-quarters of the universe and drives cosmic expansion. Dark matter makes up about a quarter of the universe and exerts a gravitational pull on visible, "normal" matter and light.

The H0LiCOW astronomers studied three such galaxies, each of which is bending light from an even more distant quasar, a cosmic object whose brightness fluctuates randomly. In each case the gravitational lens creates multiple images of the quasar.

Because mass is not evenly distributed through these massive galaxies, some areas bend or slow light more than others. So light from the quasar will arrive at slightly different times depending on the route it takes through the lens, just as drivers who set off from one city to another at the same time, but travel by different routes, will arrive at different times. By analyzing that "traffic delay," the researchers could arrive at a figure for the Hubble Constant.

Eduard Rusu, a postdoctoral researcher at UC Davis, irst author on one of five papers describing the work, due to be published in the Monthly Notices of the Royal Astronomical Society, measured the distribution of mass along the line of sight from quasar to telescope. Other team members measured the time delay for light, and the distribution of mass within the lensing galaxy.

"These three things allow us to get a precise measure of the Hubble Constant," said Chris Fassnacht, a physics professor at UC Davis and a member of the international H0LiCOW collaboration which carried out the work.

The Hubble Constant estimate from H0LiCOW, 71.9±2.7 kilometers per second per megaparsec, is accurate to 3.8 percent. The figure is in close agreement with measurements by other astronomers based on observations of supernovae, or of variable stars called Cepheids. But these estimates are rather different from that obtained from the Planck space telescope, which measured radiation from the cosmic microwave background.

The Planck measurement does rely on some assumptions, for example that the universe is flat, Fassnacht said. Or, the difference could be a statistical fluctuation that will disappear as the estimates get better — or it could be something more exciting.

"If you still see something when the error bars shrink, maybe it's new physics, beyond the Standard Model of cosmology," Fassnacht said. The H0LiCOW team plans to shrink those error bars by carrying out the same measurements for up to 100 lensed quasars, Fassnacht said.

"An accurate measurement of the Hubble constant is one of the most sought-after prizes in cosmological research today," highlights team member Vivien Bonvin, from EPFL, Switzerland.

The Hubble image at the top of the page shows spiral galaxy M66 that lies a mere 35 million light-years away. About 100 thousand light-years across, the island universe is well known to astronomers as a member of the Leo Triplet of galaxies. In M66, pronounced dust lanes and young, blue star clusters sweep along spiral arms dotted with the tell-tale glow of pink star forming regions.The bright, spiky stars lie in the foreground, within our own Milky Way Galaxy, but many, small, distant background galaxies can be seen in the cosmic snapshot.

The Daily Galaxy via ESA/Hubble Information Center and UC at Davis

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