The phenomenon that devastates our idea of ​​the expansion of the universe

A team of researchers has used a new technique to measure the rate of expansion of the universe. Their results contradict previous estimates and reopen the debate

We know that the universe is constantly expanding, but scientists cannot agree on how fast it is expanding. Now, a team of researchers has applied a new method to make these measurements that uses light from the explosion of a distant star, and their results are going to add fuel to the fire of this controversy.

The universe has been in constant expansion since the outbreak of the Big Bang, about 13.7 billion years ago. To measure the rate at which this expansion occurs, the researchers use the Hubble Constant. However, astrophysicists use two different ways to measure this constant that give different results.

Some look at objects relatively close to Earth to determine how fast they are moving away from our planet, which is called the cosmic distance scale. With it they have determined that the universe is expanding at a speed of 73 kilometers per second per million parsecs (km/s/Mpc). Others use observations of the cosmic microwave background—the residual light from the Big Bang firecracker—and get a speed of about 67 km/s/Mpc.

This discrepancy between the data obtained with both methods is known as the Hubble stress. And it may be due to both errors in the measurement system and the fact that we still have a lot to learn about the mechanisms of the cosmos.

Now, a team of researchers, led by Patrick Kelly, a professor of astrophysics at the University of Minnesota, has used a new method to measure the Hubble constant that has yielded a different number—although similar to that obtained by observing the distant universe. —, 66.6 km/s/Mpc with an uncertainty of 7 percent, less than in other similar observations.

How it works

The team has built on the work of the Norwegian astrophysicist Sjur Refsdal, who in 1964 suggested that another way to measure the Hubble constant is by observing the light of supernovae, the last step in the evolution of stars that ends in a powerful and bright burst.

Refsdal suggests that if the light from the explosion on its way to Earth passes close to a massive object—such as a cluster of galaxies—it is affected by its gravitational grip and bends and deforms, causing different images of the object to appear. . Something similar to what happens when we look at the bottom of a glass of water. This is known as gravitational lensing.

Some of these light paths will be longer and some will be shorter, so a single supernova would appear several times at slightly offset positions in the sky. That delay between each appearance would correspond to the total distance traveled by its light, so combining these delays with knowledge of the speed at which the supernova was moving away from us would give us a value for the Hubble constant.

In 2014, the same phenomenon that Refsdal describes occurred, and Kelly and her team were there to observe it. One such supernova occurred about 14 billion light-years from Earth, and the researchers used the gravitational lensing method to correctly predict the arrival of its image nearly a year later. Now the team has used that data to measure the rate of expansion of the universe.

“This is unlike anything that’s been done before,” says Kelly. “If the value of the Hubble constant turns out to be 73 as local measurements would indicate at this point, then there must be something wrong with our understanding of galaxy cluster lensing and these models are routinely used to study the universe. far”.

The researchers are already working to obtain new measurements with this method. If the value of 66.6 km/s/Mpc is maintained, it would force us to rethink our theories about the nature of the mysterious dark matter, that invisible matter that accounts for 85% of all matter in the universe, as well as the so-called model standard of cosmology.

That moment could come soon. The James Webb Space Telescope will carry out a measurement with its Hope instrument in a few months, and the Vera Rubin Observatory in Chile, which will start up next year, will make it possible to find a greater number of this type of supernovae.