- The approach is using gravitational lensing.
- Astronomers measured the brightness of galaxies in different ranges, including infrared, in a region of the sky that is 450 square degrees.
- The authors added infrared images to the Dark Energy Survey, which was performed by another team in the optical range.
Astrophysicists discovered new results by studying the distribution of matter in the universe. There are at least two ways to do this. Both rely on different aspects of the CDM model. Lambda-CDM model is a parametrization of the Big Bang cosmological model in which the universe contains three major components: first, a cosmological constant denoted by Lambda (Greek Λ) and associated with dark energy; second, the postulated cold dark matter (abbreviated CDM); and third, ordinary matter.
The first method is based on the observation of relic radiation emitted when the Universe was only 380,000 years old. This work was done by the Planck project team.
The second approach uses gravitational lensing. The fact is that the gravity of massive objects deflects light rays, working as a lens. By measuring the distortions that the light of distant galaxies has undergone, it is possible to reconstruct the mass distribution between them and the observer. It is clear that the distribution of mass in the universe does not depend on how we measure it. And if there are no errors in our theories, then the results obtained by different methods should be the same. But that was not the case.
The scientists involved in the analysis of new data were hoping to resolve this controversy. Instead, they found that it had grown even larger. Now there is only one chance in a hundred that all the calculations are correct, and the difference is caused by unavoidable measurement errors.
In order to use the effect of gravitational lensing, you need to know the distance to different light sources. In this case, millions of distant galaxies acted as such distant candles, or beacons.
Scientists find the redshift of a galaxy by measuring its brightness in different colors, such as blue, green, and red. The result is even more accurate if you add infrared (IR) data. This is exactly what the staff of the Kilo-Degree Survey (KiDS) project did. Astronomers measured the brightness of galaxies in different ranges, including infrared, in a region of the sky that is 450 square degrees. Although this is only 1% of the entire celestial sphere, for such accurate measurements, this is a solid coverage.
Scientists hoped that adding IR data would reduce the contradiction, but it turned out exactly the opposite. To test this again, the authors added infrared images to the Dark Energy Survey, which was performed by another team in the optical range. Again, the refinement of distances to galaxies using IR data increased the discrepancy with the Planck data.
The team is now working to include even more galaxies in the sample. This will increase the accuracy of measurements and either reduce the contradiction with the Planck data, or strengthen it even more.
Astrophysicists suggested that the properties of dark energy, which accelerates the expansion of the Universe, change over time. Relic radiation was emitted more than 13 billion years ago, just 380,000 years after the Big Bang. But observations of gravitational lensing tell of much later epochs.
Interestingly, the value of the Hubble constant, which determines the rate of expansion of the Universe, also depends on whether to measure it from data on relic radiation or in another way. And this contradiction can also be eliminated by assuming that dark energy changes.
However, this will not solve all the problems with the Hubble constant: using the third method of measuring it, astronomers got a result that differs from the first two. The Hubble constant is a unit that describes how fast the universe is expanding at different distances from a particular point in space. It is one of the keystones in our understanding of the universe’s evolution and researchers are mired in a debate over its true value.
There are still unknown questions about the universe and we continue to discover and understand.