New Measurement Strengthens The Case That Our Theory Of The Cosmos Is Missing Something

Two of the gravitational lenses observed by the team. NASA, ESA, S.H. Suyu (Max Planck Institute for Astrophysics, Technical University of Munich, and Academia Sinica Institute of Astronomy and Astrophysics), and K.C. Wong (University of Tokyo’s Kavli Institute for the Physics and Mathematics of the Universe)

For the last few years, cosmologists have been dealing with an unexpected finding that threatens to undermine the standard model of cosmology. Measurements of the expansion rate of the Universe get different values depending on if you measure the very first light in the universe or “closer” objects.

According to the standard model, the discrepancy shouldn’t be there but more refined estimations continue to show it. A new measurement, from the H0LiCOW (H0 Lenses in COSMOGRAIL's Wellspring) project, estimates an expansion rate of 73 kilometers per second per megaparsec, with a 2.4 percent uncertainty.

This means that a point locater 3.3 million light-years away (one megaparsec) appears to be moving away from us at 73 kilometers per second due to the expansion of the universe. The value obtained from the cosmic microwave background, the first free-moving light in the cosmos, is instead 67 kilometers per second per megaparsec. The difference between the two is significant enough to put a big question mark on what we know.

"If these results do not agree, it may be a hint that we do not yet fully understand how matter and energy evolved over time, particularly at early times," H0LiCOW team leader Sherry Suyu of the Max Planck Institute for Astrophysics in Germany, the Technical University of Munich, and the Academia Sinica Institute of Astronomy and Astrophysics in Taipei, Taiwan, said in a statement.

The measurement was achieved by studying gravitationally lensed quasars, which have already been employed in another successful discovery this week. A galaxy is a quasar when its core is so bright it outshines all the stars within itself. It is the light from these that encounter the space-time distortion created by massive foreground galaxies.

The distortion is referred to as a gravitational lens, which can create multiple images of the same background objects. So when Hubble looks at these lensing galaxies, it sees four images of the quasars instead of just one. While the images are of the same objects, each photon took a slightly different path through the lens, so each image has a different time delay.
 
"The length of each time delay indicates how fast the universe is expanding," said Kenneth Wong of the University of Tokyo's Kavli Institute for the Physics and Mathematics of the Universe, lead author of the H0LiCOW collaboration's most recent paper. "If the time delays are shorter, then the universe is expanding at a faster rate. If they are longer, then the expansion rate is slower."
 
The team hopes to reduce the uncertainty of the value to 1 percent. For that to happen, they need not only the James Webb Space Telescope but also to go from 10 to 30 lensed quasars. Future and present surveys could push that number even higher. Hopefully, we will soon get a better idea of just what’s going on with the universe.
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