Hubble measurements suggest that the disparity in Hubble's constant calculations is not a coincidence


IMAGE: Nearly 200,000 light-years from Earth, the Great Magellanic Cloud, a satellite galaxy of the Milky Way, floats in space, in a long, slow dance around our galaxy. As…
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Credit: NASA, ESA. Acknowledgment: Josh Lake

The measurements of Hubble's current expansion rate do not match the expected rate based on how the Universe appeared shortly after the Big Bang more than 13 billion years ago. Using new data from the NASA / ESA Hubble Space Telescope, astronomers have significantly reduced the possibility that this discrepancy is a coincidence.

Using new observations from the NASA / ESA Hubble Space Telescope, researchers have improved the foundations of the cosmic distance scale, which is used to calculate precise distances to nearby galaxies. This was done by observing pulsating stars called Cepheid variables in a neighboring satellite galaxy known as the Large Magellanic Cloud, which is now estimated to be 162,000 light-years away. By defining distances to galaxies that are increasingly distant, these Cepheid variables are used as milestone markers. Researchers use these measurements to determine how fast the Universe is expanding over time, a value known as the Hubble constant.

Before Hubble was launched in 1990, the estimates of the Hubble constant varied by a factor of two. In the late 1990s, the Hubble Space Telescope Key Project on the Extragalactic Distance Scale refined the value of the Hubble constant to 10 percent, achieving one of the key goals of the telescope. In 2016, astronomers using Hubble discovered that the Universe is expanding five to nine percent faster than previously calculated by refining the Hubble constant measurement and further reducing the uncertainty to only 2.4 percent. In 2017, an independent measure supported these results. This latest research has reduced the uncertainty in Hubble's constant value to an unprecedented 1.9 percent.

This research also suggests that the probability that this discrepancy between the measurements of the current expansion rate of the Universe and the expected value based on the early expansion of the Universe is a coincidence is 1 in 100,000, a significant improvement over a previous estimate last year 3,000.

"Hubble's tension between the early and later Universe may be the most exciting development in cosmology in decades," said Principal Investigator and Nobel Laureate Adam Riess of the Space Telescope Science Institute (STScI). and Johns Hopkins University, in Baltimore, EE. UU "This mismatch has been growing and now it has reached a point that is really impossible to dismiss as a coincidence, this disparity could not happen by chance".

As the measurements of the equipment became more accurate, his calculation of the Hubble constant remained inconsistent with the expected value derived from observations of the early Universe expansion carried out by the Planck satellite of the European Space Agency. These measurements map a residual glow of the Big Bang known as the Cosmic Microwave Background, which helps scientists predict how the early Universe would likely have become the rate of expansion that astronomers can measure today.

The new estimate of the Hubble constant is 74.03 kilometers per second per megaparsec [1]. The number indicates that the Universe is expanding at a speed about 9 percent faster than implied in the Planck observations of the early Universe, which gives a value for the Hubble constant of 67.4 kilometers per second per megaparsec.

To reach this conclusion, Riess and his team badyzed the light of 70 Cepheid variables in the Large Magellanic Cloud. Because these stars shine and attenuate at predictable rates, and the periods of these variations give us their luminosity and, therefore, distance, astronomers use them as cosmic landmarks. The Riess team used an efficient observation technique called Drift And Shift (DASH) that uses Hubble as a "point-and-shoot" camera to take quick pictures of bright stars. This avoids the slowest step of anchoring the telescope with guide stars to observe each star. The results were combined with observations made by the Araucaria Project, a collaboration between astronomers from institutions in Europe, Chile and the United States, to measure the distance to the Large Magellanic Cloud by observing the attenuation of light when a star pbades by. . Your partner in a binary-star system.

Because cosmological models suggest that the observed values ​​of the expansion of the Universe must be the same as those determined in the Cosmic Microwave Fund, a new physics may be necessary to explain the disparity. "Previously, theorists were telling me:" It can not be … It's going to break everything. "Now they're saying," We could actually do this, "said Riess.

Several scenarios have been proposed to explain the discrepancy, but there is still no conclusive answer. An invisible form of matter called dark matter can interact more strongly with normal matter than astronomers thought. Or perhaps dark energy, an unknown form of energy that permeates space, is responsible for accelerating the expansion of the Universe.

Although Riess does not have an answer to this disconcerting disparity, he and his team intend to continue using Hubble to reduce the uncertainty in their measure of the Hubble constant, which they expect to decrease to 1 percent.


The results of the team have been accepted for publication in The astrophysical diary.


[1] This means that for every 3.3 million light years farther, a galaxy is from us, it seems to be moving about 74 kilometers per second faster, as a result of the expansion of the Universe.

More information

The Hubble Space Telescope is an international cooperation project between ESA and NASA.

The team of astronomers in this study consists of Adam G. Riess (Johns Hopkins University, USA, STScI, USA), Stefano Casertano (STScI, USA), Wenlong Yuan (Johns Hopkins University, USA), Lucas M. Macri (Texas A & M) University, USA), Dan Scolnic (Duke University, USA)

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Adam Riess

Space Telescope Science Institute

Baltimore, USA

Tel: +1 410 338 6707

Email: [email protected]

Bethany Downer

ESA / Hubble, responsible for public information

Garching, Germany

Email: [email protected]

Resignation: AAAS and EurekAlert! they are not responsible for the accuracy of the press releases published in EurekAlert. through contributing institutions or for the use of any information through the EurekAlert system.

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