NASA scientists suggest we may not yet understand the universe’s early expansion.
A group of astronomers working with the Hubble Space Telescope have used the gravitational lensing of galaxies to measure the expansion of the universe. The rate of this expansion is known as the Hubble constant, and the new measurements, while completely independent, agree very closely with previous measurements of the universe’s current expansion in the local universe. However, the measurements do not agree with a rate found by ESA’s Planck satellite for the expansion of the early universe. The Planck measurements agree with our current understanding of the cosmos; so the new readings are eye-opening.
“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 lead astronomer Sherry Suyu.
The measurements were made by looking at galaxies placed between Earth and very distant quasars, the extremely bright centers of galaxies orbiting closely around their central supermassive black holes. The light from the quasars bends around the galaxies as a result of strong gravitational lensing. This creates multiple images of the quasar.
An example of gravitational lensing
Galaxies do not create perfectly round distortions in space and the galaxies and quasars are not perfectly aligned. Because of this, the light from the different quasar images follows paths which have slightly different lengths. The brightness of quasars also changes over time, and by combining these two properties, astronomers can see the different images flicker at different times. The delays between them depends on the lengths of the paths the light has taken and are directly related to the value of the Hubble constant.
The team has successfully measured the Hubble constant to within 3.8%, which is an important achievement: “An accurate measurement of the Hubble constant is one of the most sought-after prizes in cosmological research today,” explains team member Vivien Bonvin. Suyu adds: “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.”