London: The universe is expanding at a rate faster than previously believed, scientists have confirmed, a finding that may completely overturn our understanding of the cosmos. Astronomers using the NASA/ESA Hubble Space Telescope have made a measurement of how fast the Universe is expanding.
The beating heart of the Crab Nebula. Image courtesy: NASA/ESA
The Hubble constant - the rate at which the Universe is expanding - is one of the fundamental quantities describing our Universe. Astronomers from the H0LiCOW collaboration, led by Sherry Suyu from the the Max Planck Institute for Astrophysics in Germany, used telescopes in space and on Earth to observe five galaxies in order to arrive at an independent measurement of the Hubble constant.
The centre of the Tarantula Nebula in the Large Magellanic Cloud. Image courtesy: NASA/ESA
The new measurement is in excellent agreement with other measurements of the Hubble constant in the local Universe that used Cepheid variable stars and supernovae as points of reference. 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.
The Pinwheel Galaxy. Image courtesy: NASA/ESA
Planck measured Hubble constant for the early Universe by observing the cosmic microwave background, researchers said. 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," said Suyu.
The Westerlund 2. Image courtesy: NASA/ESA
The targets of the study were massive galaxies positioned between Earth and very distant quasars - incredibly luminous galaxy cores. The light from the more distant quasars is bent around the huge masses of the galaxies as a result of strong gravitational lensing. This creates multiple images of the background quasar, some smeared into extended arcs.
The Andromeda Galaxy. Image courtesy: NASA/ESA
Since galaxies do not create perfectly spherical distortions in the fabric of space and the lensing galaxies and quasars are not perfectly aligned, the light from the different images of the background quasar follows paths which have slightly different lengths. Since the brightness of quasars changes over time, astronomers can see the different images flicker at different times, the delays between them depending on the lengths of the paths the light has taken. These delays are directly related to the value of the Hubble constant.
The Milky Way ten billion years ago. Image courtesy: NASA/ESA
Using the measurements of time delays between the multiple images, as well as computer models, the team determined the Hubble constant to a high precision: 3.8 per cent. "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," said Suyu.