Hubble takes another step in determining the rate of expansion of the universe

Since the discovery of, or almost, the expansion of the universe, the question has plagued astrophysicists. How fast is this expansion continuing today? Because observations and theory do not give the same answer. Today, the Hubble Space Telescope provides additional precision.

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[EN VIDÉO] Interview: why is the universe expanding?
With the discovery of the expansion of the universe came other questions: how fast is this expansion happening? is there acceleration? or slow down? Futura-Sciences interviewed Aurélien Barrau, an astrophysicist specializing in cosmology and author of the book Des univers multiples.

Our universe is expanding. there is no doubt. What is being discussed is speed which continues today this movement. Its current rate of expansion – which translates to what physicists baptized, the Hubble constantly. It was in honor of the American Edwin Hubble who discovered the phenomenon of the expansion of the universe and made the first measurements of it in the 1920s. And the tribute stone is further strengthened today as researchers unveil new ones new results more accurate than ever. Obtained from data collected over more than 30 years by The Hubble Space Telescope.

It must be remembered that measurement was precisely one of the main reasons for the existence of this instrument. Efforts that have been made since the 1970s were aimed at developing a tool that could solve cepheider. Because the Cepheids, variable starshas long served as cosmic markers, a kind of standard gauge for measure distances in the universe. Since 1912, exactly. They can both be seen in ours The Milky Way only in galaxies distant, thanks to the Hubble Space Telescope, up to about 80 millionlight years.

It was when Hubble was launched in the 1990s that the first series of Cepheid observations was made. With the main purpose of refining the measurement of the distances from galaxies close to ours. In the early 2000s, the effort was for astronomers was rewarded. They were thus able to derive a value of Hubble constantly with an accuracy of 10%. A value of 72 plus or minus 8 kilometers per second per. megaparsec (km / s / Mpc).

Which value is correct?

To refine this value, the researchers then added new cameras to the space telescope. With the idea of ​​achieving an accuracy of 1%. One idea in particular led to the collaboration Supernova, H0, for the equation of the state of dark energy (SH0ES).

The new results published today by the researchers are thus based on a sample of cosmic markers that has more than doubled. They also incorporate an updated analysis of past data. And a total of 42 supernovae – knowing that Hubble is witnessing one supernova explosion per year, approximately … – also useful for determining distances in the universe. Thus, given the size of their sample, astronomers estimate for only one chance out of a million, the possibility “from an unfortunate draw”. And give a value of the Hubble constant of about 73 km / s / Mpc. Exactly 73.04 +/- 1.04 km / s / Mpc.

The problem is that from the measurements of Planck mission (European Space Agency, ESA) on our early universe and according to the standard cosmological model, theorists predict a value of the Hubble constant that should be 67.5 plus or minus 0.5 km / s / Mpc. So where does this discrepancy come from? Astronomers still do not know. But it is possible that they have to look for the answer somewhere in the new laws of physical. ONE much recent study for example, trying to explain the discrepancy using a “world mirror» invisible particles that would only interact with our world via gravity.

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