Hubble provides the most accurate measurement of the expansion of the universe to date

Hubble provides the most accurate measurement of the expansion of the universe to date

By analysing more than 30-year-old data collected by the Hubble Space Telescope, NASA has been able to measure the rate of expansion of the universe in the most accurate way to date.

Astronomers have known for almost a century that the universe is expanding. The further the galaxies are apart, the faster they move. The speed at which they move, depending on the distance to the Earth, is defined as the constant Hubble. Measuring this value was one of the main objectives of the telescope.

To measure the constant Hubble, astronomers analyse distances to different types of objects whose brightness is well known. To study relatively close objects, astronomers rely on Cepheids. This is a class of stars that pulsate according to a predictable pattern.

More accurate constant

Over the past few decades, measurements of these objects have allowed astronomers to calculate a permanent Hubble of about 70 km per second per megaparsec from the Earth at a speed of about 70 km per second, and this speed increases by 70 km/s with each megaparsec.

However, in recent years, teams have used other methods to try to refine this estimate, and the results have varied widely. For this new work, the NASA team has collected and analysed the most complete catalogue of these objects to date to make the most accurate measurement of this constant. All these objects, isolated in forty-two galaxies, have been obtained by Hubbles over the past thirty years.

From this work, the constant Hubble that the team calculated was 73 km/s/Mpk, plus/minus 1 km/s/Mpk. This reduces the error to only 1.4 per cent, which is more accurate than other measurements. This new clarification can help astronomers improve cosmological models by better determining their age or future.

Large gap that raises questions

However, the main mystery remains: it was predicted that the rate of expansion of the universe would be slower than Hubble actually sees. By combining the Standard Cosmological Model of the Universe and Measurements carried out by the mission of the European Space Agency Plank, astronomers predict a lower value of the permanent Hubble: 67.5 km/s/Mpk.

According to researchers, given the large size of Hubble's sample, there is only one chance per million that astronomers are wrong in the new estimate, but the measurements of the Standard Model of Cosmology are also very reliable. Astronomers still cannot explain the difference between the rate of expansion of the local universe and the early universe, but the answer may be related to new physics.

This mystery can be answered by the James Webb telescope, which will expand Hubble's work by providing long-range or higher-resolution space markers.