Largest 3D map of the universe: More evidence of variable dark energy

There is growing evidence in cosmology that so-called dark energy is not constant, but changes “in unexpected ways” over the course of time. This has now been announced by the research team responsible for the largest three-dimensional map of the universe. The data collected in the first year after the Dark Energy Spectroscopic Instrument (DESI) was put into operation had already pointed to this biggest discovery in cosmology for decades. Data from the first three years of research that has now been analyzed confirms this. However, it cannot yet be sufficiently ruled out that this is not a statistical anomaly.

Possibly, the most important discovery in decades

As the DESI Collaboration now explains, almost 15 million galaxies and quasars were measured with the instrument within the first three years of operation. The data set is thus more than twice as large as that which contained the first indications of variable dark energy, while at the same time being significantly more accurate. On their own, the data would still confirm the standard model of cosmology and thus also a constant dark energy, but together with other increasingly precise measurements, the new picture emerges. This involves measuring the cosmic microwave background, supernovae and weak gravitational lenses.

Taken together, the measurements indicate that the influence of dark energy is decreasing over time. This would have significant consequences because the fate of the cosmos as a whole depends on the balance between normal matter and dark energy, among other things. This balance is the fundamental component for the expansion of the universe. However, it is still too early to announce a discovery; depending on how the various measurement results are combined, the probability is between 2.8 and 4.2 sigma. 5 sigma is considered the threshold for a certain discovery.

Data available to all

After Edwin Hubble and others proved at the beginning of the 20th century that the universe was expanding, researchers long assumed that this expansion was slowing down. It was not until 1998, however, that the analysis of distant supernovae revealed that, on the contrary, the expansion was actually accelerating. This was awarded the Nobel Prize in Physics in 2011. Dark energy is thought to be responsible for this acceleration, but its nature is still extremely mysterious. The DESI is supposed to help explain it, and the impression is growing that this is exactly what is happening. If dark energy were indeed not constant, this would be the most important discovery since accelerated expansion.

The DESI has been collecting spectra of millions of galaxies since 2021, covering around a third of the night sky. From the spectra, researchers can not only deduce the chemical composition of the emitting objects, but also their relative distance and proper motion, depending on how far they are shifted into the red. The aim is to create the most comprehensive map of the expanding universe. Thanks to robot-controlled glass fibers, the instrument can simultaneously capture the spectra of 5,000 galaxies and measure up to 150,000 objects in a good night. The first complete data set (DR1) is now available, as are the studies based on it.

(mho)