There is a mystery about the expansion rate of our Universe, and the Hubble Space Telescope is looking into this issue.

Scientists have a new, more accurate measurement of the expansion of the universe thanks to decades of data from the Hubble Space Telescope.

A new analysis of data from the 32-year-old Hubble Space Telescope continues the observatory’s long-standing search to better understand how fast the universe is expanding and how much that expansion is accelerating.

The number that astronomers use to measure this expansion is called the Hubble constant (not after the telescope, but after the astronomer Edwin Hubble who first measured it in 1929). The Hubble constant is difficult to determine, given that different observatories studying different regions of the universe have given different answers. But the new study expresses confidence that Hubble’s latest effort matches exactly the expansion it sees, though it still differs from other observatories.

The new study confirms previous expansion rate estimates based on Hubble observations, showing an expansion of about 45 miles (73 kilometers) per megaparsec. (A megaparsec is a measure of distance, equal to one million parsecs, or 3.26 million light-years.)

On the subject: The best images of the Hubble Space Telescope of all time!

“Given Hubble’s large sample size, the odds of astronomers getting it wrong because of a bad draw is only one chance in a million…that’s the general threshold for taking a problem in physics seriously,” NASA said in a statement Thursday. (May 19), paraphrasing Nobel Prize winner and study lead author Adam Riess.

Riess works at the Space Telescope Science Institute (STScI), which operates Hubble, and at Johns Hopkins University in Baltimore, Maryland.

Riess and his collaborators received the Nobel Prize in 2011 after Hubble and other observatories confirmed that the expansion of the universe is accelerating. Riess calls this latest Hubble work “a standout piece,” given that it draws on virtually the telescope’s entire history, 32 years in space, to provide an answer.

The Hubble data captured the observed expansion rate in a program called SHOES (Supernova, H0, for the dark energy equation of state). The data set doubles the previous sample of measurements and also includes more than 1,000 Hubble orbits, NASA said. The new measurement is also eight times more accurate than expected from Hubble’s capabilities.

Attempts to measure the expansion rate of the universe usually focus on two distance markers. Some of these are the Cepheids, variable stars that get brighter and dim at a constant rate; their usefulness has been known since 1912, when astronomer Henrietta Swan Leavitt noted their importance in the images she viewed.

Cepheids are good for mapping distances within the Milky Way (our galaxy) and in nearby galaxies. For longer distances, astronomers rely on Type 1a supernovae. These supernovae have a constant luminosity (intrinsic brightness), which makes it possible to accurately estimate their distance based on how bright they appear in telescopes.

In a new study, NASA said: “The team measured 42 supernova markers using Hubble. Since they explode at a rate of about once a year, Hubble has recorded as many supernovae as possible for all practical purposes. measurements of the expansion of the universe. (Again, Hubble has been in space for about 32 years, having launched on April 24, 1990; in December 1993, the astronauts fixed a mirror flaw that had hampered early work.)

But the expansion rate still does not have a perfect match between different efforts. The new study says the Hubble measurements are roughly 45 miles (73 kilometers) per megaparsec. But when observations of the deep universe are taken into account, the speed slows down to about 42 miles (67.5 km) per megaparsec.

Observations of the deep universe are mainly based on measurements from the European Space Agency’s Planck mission, which observed the “echoes” of the Big Bang that formed our universe. The echo is known as the cosmic microwave background. NASA said astronomers “can’t figure out why there are two different values” but suggested that we might need to rethink the basics of physics.

Riess said the best way to see the rate of expansion is not by its exact value at the time, but by its effects. “I don’t care about the specific meaning of the expansion, but I like using it to study the universe,” Riess said in a NASA statement.

More measurements are expected over the next 20 years with the James Webb Space Telescope, which is completing commissioning work in deep space before beginning to study some of the first galaxies. Webb, NASA said, will look at Cepheids and Type 1a supernovae “from a greater distance or at a higher resolution than what Hubble can see.” This, in turn, can refine Hubble’s observed velocity.

An article based on the study will be published in the Astronomical Journal. A preview is available at

Follow Elizabeth Howell on Twitter @howellspace. Follow us on Twitter @Spacedotcom or Facebook.

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