Astronomers get their wish, and a cosmic mystery deepens

By | January 1, 2021

Natalie Wolchover writes:

On December 3, humanity suddenly had information at its fingertips that people have wanted for, well, forever: the precise distances to the stars.

“You type in the name of a star or its position, and in less than a second you will have the answer,” Barry Madore, a cosmologist at the University of Chicago and Carnegie Observatories, said on a Zoom call last week. “I mean …” He trailed off.

“We’re drinking from a firehose right now,” said Wendy Freedman, also a cosmologist at Chicago and Carnegie and Madore’s wife and collaborator.

“I can’t overstate how excited I am,” Adam Riess of Johns Hopkins University, who won the 2011 Nobel Prize in Physics for co-discovering dark energy, said in a phone call. “Can I show you visually what I’m so excited about?” We switched to Zoom so he could screen-share pretty plots of the new star data.

The data comes from the European Space Agency’s Gaia spacecraft, which has spent the past six years stargazing from a perch 1 million miles high. The telescope has measured the “parallaxes” of 1.3 billion stars — tiny shifts in the stars’ apparent positions in the sky that reveal their distances. “The Gaia parallaxes are by far the most accurate and precise distance determinations ever,” said Jo Bovy, an astrophysicist at the University of Toronto.

Best of all for cosmologists, Gaia’s new catalogue includes the special stars whose distances serve as yardsticks for measuring all farther cosmological distances. Because of this, the new data has swiftly sharpened the biggest conundrum in modern cosmology: the unexpectedly fast expansion of the universe, known as the Hubble tension.

The tension is this: The cosmos’s known ingredients and governing equations predict that it should currently be expanding at a rate of 67 kilometers per second per megaparsec — meaning we should see galaxies flying away from us 67 kilometers per second faster for each additional megaparsec of distance. Yet actual measurements consistently overshoot the mark. Galaxies are receding too quickly. The discrepancy thrillingly suggests that some unknown quickening agent may be afoot in the cosmos. [Continue reading…]

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