The most accurate map of the dark matter in our universe is rare

DES is an effort to map as many galaxies as possible to map dark material, and this is possible because the gravity of dark matter plays an important role in governing how these galaxies are distributed. From August 2013 to January 2019, dozens of scientists came together to use Chile’s four-meter Victor M. Blanco telescope to study the near-infrared sky.

There are two keys to creating a map. The first is simply to observe the location and distribution of galaxies throughout the universe. This arrangement tells the scientist where the highest concentrations of dark matter are.

The second is the observation of gravitational lenses, a phenomenon in which light emitted by galaxies gravitates to dark matter as it moves through space. The effect is similar to looking through a magnifying glass. Scientists use gravitational lenses to deduce how much space dark matter around them takes up. The more distorted the light, the darker the dark matter.

The latest results take into account the first three years of DES data, which includes more than 226 million galaxies observed in 345 nights. “We are now able to map dark matter in the southern hemisphere,” says Niall Jeffrey, a researcher at University College London and École Normale Supérieure in Paris, who is leading the DES project.

In general, the data is consistent with the so-called Standard Cosmological Model, which states that the universe was created in the Big Bang and that the total mass energy content is 95% dark matter and dark energy. And the new map gave scientists a more detailed look at some of the vast structures of dark matter in the universe that are otherwise invisible to us. The brightest points on the map represent the highest concentrations of dark matter, and form sets and halos around very low-density voids.

But some of the results were amazing. “We’ve found notes that the universe is smoother than expected,” Jeffrey says. “These tips are also seen in other gravitational lens experiments.”

This is not what general relativity predicts, as it suggests that dark matter should be more clumsy and so evenly distributed. The authors write In one of 30 papers “Although the evidence is by no means definitive, we are beginning to see traces of the new physics.” For cosmologists, “this would be consistent with changing the laws of gravity described by Einstein,” says Jeffrey.

While the consequences are dire, caution is key, as we still know very little about dark matter (something we have yet to directly observe). For example, Jeffrey warns that “because of the complex astrophysics, if the surrounding galaxies were formed in a strange way, our lens results would be misleading.”

In other words, there could be some exotic explanations of the results, perhaps in ways that are compatible with general relativity. That would be very quick for any astrophysicist to rely on Einstein’s correctness for a lifetime’s work. And let’s not forget: general relativity has adapted very well all other tests that has been thrown at him over the years.

The results are already generating waves, although more DES data is being published. “Already, astronomers are using these maps to study the structures of the cosmic network and to better understand the connection between galaxies and dark matter,” says Jeffrey. Maybe we shouldn’t wait too long to find out if the results are really clear or if we need a massive rewriting to understand the universe.