Scientists disagree. A new measurement by NASA’s Hubble Space Telescope of how fast the universe is expanding could lead to a new interpretation of one of the fundamental properties of the universe.
It is not useful to think of a center of the universe, since this could be infinite. But what scientists do know is that the universe is expanding, not necessarily from one center, but that all galaxies are moving away from each other. At what velocity?
The so-called Hubble constant refers to this measurement, the exact value of which is often debated. The Hubble constant is the ratio of the speed and distance of one galaxy to another, which is estimated to be approximately 80 kilometers per second per Mega Parsec (a unit of length in astronomy; 1 megaparsec (Mpc) equals about 3.26 million light years). Last year a study published in the Astrophysical Journal concluded that galaxies that are closest to each other are moving away faster than the most distant galaxies.
But the Hubble constant has been widely debated, and there is still no scientific consensus on the rate at which the universe is expanding.
Now, a new study suggests that this speed could be even higher than previously believed. In fact, the authors, University of Chicago professor Wendy Freedman and her colleagues, differ in the proportions of the universe measured by the European Space Agency’s Planck satellite.
And they are not the only ones. As more research points to a discrepancy between predictions and observations, scientists are considering whether it is necessary to develop a new model for the physics of the universe in order to explain it more accurately.
In a new paper accepted for publication in The Astrophysical Journal , Freedman and his team have announced a new measurement of the Hubble constant by observing a red giant. Measurements, made with Hubble, indicate that the expansion rate of the nearby universe is just under 70 kilometers per second per megaparsec (km / sec / Mpc). (One parsec is equivalent to 3.26 light years away); 10 km / sec / Mpc less than the original measurements, and also slightly less than the value of 74 km / sec / Mpc recently reported by the Hubble team SH0ES using Cepheid variables, which are stars that pulse at regular intervals corresponding to their maximum brightness.
Results that, although they seem unimportant, according to the researchers “are powerful enough to believe that there is something defective in our current model of understanding the universe.”
Why is there no exact data?
The truth is that there are several ways to calculate the Hubble constant, and all of them seem very accurate. From 67.4 km / sec / Mp that the Planck mission measured, measurements obtained from pulsars in the Milky Way that place it at 73.4 km / sec / Mp, to predictions that it could reach 80 km / sec / Mp. Why so much discrepancy in the results?
Astronomers have looked for anything that might be causing the mismatch. “Naturally, questions arise as to whether the discrepancy stems from some aspect that astronomers do not yet understand about the stars we are measuring, or whether our cosmological model of the universe remains incomplete,” says Freedman. “Or maybe they both need to be improved.”
How do you measure the speed of the universe?
This is how scientists can measure the rate of expansion through red giants, a stage in the life of stars that are about to die (and that our Sun will also experience 4.5 billion years from now): at a certain point , the star undergoes a catastrophic event called a helium flash, in which the temperature rises to about 100 million degrees and the star’s structure reorganizes, ultimately dramatically decreasing its luminosity. Astronomers can measure the apparent brightness of red giant stars at this stage in different galaxies, and they can use this as a way to tell their relative distance from another point.
A mission designed to unify the value of the Hubble constant
NASA’s Wide Field Infrared Telescope (WFIRST), scheduled to launch in 2020 , will allow astronomers to better explore the value of the Hubble constant through cosmic time. WFIRST, with its Hubble resolution and a 100 times greater view of the sky, will allow a more precise view of new supernovae, Cepheid variables and red giant stars to improve distance measurements to nearby and distant galaxies.
