Space telescopes zoom in on how fast the cosmos is expanding

How fast is the universe expanding? How fast should it be? These two questions are at the heart of understanding one of the basic questions of the cosmos.

Answering them isn’t so simple. Differences between the expected and actual rates of universe expansions are usually put down to measurement error, but now NASA has determined that something else might be at play.

The US space agency’s two flagship space telescopes – James Webb (JWST) and Hubble – have now undertaken measurements of the rate of expansion.

A spiral galaxy.
At 130m light years away, the supernova NGC 5468 is one of the pieces of the puzzle used to interpret the expansion of the cosmos. Credit: NASA/ESA Hubble Space Telescope.

While Hubble has spent 3 decades taking these measurements, teams have recently tasked the JWST with making similar observations as a means of verification.

No meaningful discrepancies were found.

It means the ‘Hubble Tension’ – the term given to the difference between expected and observed rates of expansion – can’t be explained by calculation disparity.

“We’ve now spanned the whole range of what Hubble observed, and we can rule out a measurement error as the cause of the Hubble Tension with very high confidence,” says Johns Hopkins University physicist Adam Riess.

The JWST took observations of Cepheid variable stars, which are pulsating stars that are used as measuring markers when understanding the distance between galaxies and universal expansion.

These relatively crisp observations confirmed by JWST were used to cross-check Hubble’s fuzzier images of Cepheid variable stars. Snapping clusters of Cepheids at a maximum distance of 130m light years, gives an unprecedented glimpse at these space phenomena.

Cepheid p42 ngc 5468 stsci 01hr59vhj7fpb7sw3cgrtaz8e5
Credit: NASA

With the data from both space telescopes reconciled, it leaves open the question of why the universe appears to be expanding faster than predictions suggest it should.

Another space telescope could solve the Hubble Tension

Understanding how quickly the universe is expanding will help to answer other questions like how old the universe is and whether this growth will continue or come to an end.

 With measurement errors ruled out, it means a different instrument might be needed to solve the puzzle.

Enter the Nancy Grace Roman Space Telescope. Due for launch by May 2027, this new telescope – named after NASA’s first chief astronomer – will have a field of view 100 times wider than Hubble.

Roman’s goal is to resolve questions related to the invisible force that drives universal expansion, known as dark energy.  It’s not the only space telescope attempting to answer the question. The European Space Agency’s ‘Euclid’ is also performing a similar task.

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