The Hubble voltage remains one of the greatest mysteries in astrophysics.
New research rules out measurement errors and raises new questions.
Baltimore - The question of how fast the universe is expanding is seemingly simple, but it leads to one of the universe's greatest mysteries, the so-called "Hubble tension."
This puzzle has puzzled astrophysics for years, as two different methods of measuring the expansion of the universe lead to two different results.
The cosmic background radiation provides an expansion rate of about 67 kilometers per second per megaparsec (one megaparsec is equivalent to 3.26 million light years).
However, if you use Cepheids, a specific type of star, to measure distance, the result is an expansion rate of around 73 kilometers per second per megaparsec.
This discrepancy between the two values is the “Hubble tension,” for which no explanation has yet been found.
One question concerns cosmology: How does the Hubble tension come about?
Some scientists suspected that a measurement error by the Hubble Space Telescope could be responsible for the “Hubble voltage”.
However, this theory was refuted by a research team led by physicist Adam Riess from Johns Hopkins University in Baltimore.
Riess, who shared the Nobel Prize in Physics with other researchers in 2011 for discovering the accelerated expansion of the universe, explains in a statement: “If measurement errors are excluded, there remains the real and exciting possibility that we have misunderstood the universe.”
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The galaxy NGC 5468 is about 130 million light-years from Earth.
It is the most distant galaxy in which the Hubble Space Telescope discovered Cepheids, which are used to determine distances in astrophysics.
The image was taken through a collaboration between the James Webb and Hubble space telescopes.
© NASA, ESA, CSA, STScI, Adam G. Riess (JHU, STScI)
To check whether the Hubble telescope produced measurement errors, Riess' team used the James Webb Space Telescope (JWST).
The results of their study were published in
The Astrophysical Journal Letters
.
Does the Hubble Space Telescope have a measurement error at long distances?
The “cosmic distance ladder” is used to calculate the expansion of the universe.
Each step of this ladder is based on the previous one, so measurement error runs through all steps.
The Cepheids, used to measure distances in space, could be more difficult to measure at greater distances because their light could mix with the light of a nearby star and be difficult to separate.
At least that was the fear when it came to data from the Hubble space telescope, because Hubble images became less clear at greater distances.
Why Cepheids are used to measure distance
Cepheids (pulsation-variable stars) change their brightness periodically - and this period is known very precisely.
The luminosity and the period of brightness fluctuation are related to each other in Cepheids - which is why research can derive the distance to the star from the brightness and the calculated luminosity.
The JWST, on the other hand, works perfectly and, with its sharp infrared vision, can see through all the dust in space and distinguish stars better.
“The combination of 'Webb' and 'Hubble' gives us the best of both worlds.
“We find that the Hubble measurements are still reliable even as we climb further up the cosmic distance ladder,” explains Riess.
He adds: “We have now covered the entire area that Hubble observed and can rule out measurement error as the cause of the Hubble voltage with great certainty.”
The Hubble telescope measures distances of up to 130 million light years
The new measurements reach a distance of 130 million light years.
“We have gone to the end of the second step of the cosmic distance ladder,” emphasizes Gagandeep Anand from the Space Telescope Science Institute, which operates the Hubble and JWST space telescopes.
“We have to find out whether we missed something and how we can connect the beginning of the universe with the present,” says Riess, summarizing the current situation.
Two telescopes that are intended to investigate the influence of dark energy in the universe could help: The ESA space telescope “Euclid” is already active, and the “Nancy Grace Roman” space telescope of the US space organization Nasa is scheduled to launch in 2027.
Only recently, the German space telescope eROSITA solved another cosmological mystery: the question of how matter is distributed and how clumped it is.
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Category list image: © NASA, ESA, CSA, STScI, Adam G. Riess (JHU, STScI)