New constraints on the presence of lightweight dark matter in the Milky Way

Dark matter, made up of particles that do not reflect, emit or absorb light, is expected to make up most of the matter in the universe. However, its lack of interactions with light prevents its direct detection using conventional experimental methods.

Physicists have been trying to devise alternative methods to detect and study dark matter for decades, but many questions about its nature and presence in our galaxy remain unanswered. Pulsar Timing Array (PTA) experiments attempt to verify the existence of so-called ultralight dark matter particles by examining the millisecond timing of an array of galactic radio pulsars (i.e. celestial bodies that emit regular millisecond radio wave pulses).

The European Pulsar Timing Array, a multinational team of researchers at different institutes that uses 6 radio telescopes across Europe to observe specific pulsars, recently analyzed the second wave of data they collected. Their paperpublished in Physical review lettersplaces more stringent constraints on the presence of lightweight dark matter in the Milky Way.

“This paper was basically the result of my first doctoral project,” Clemente Samara, co-author of the paper, told Phys.org. “The idea arose when I asked my supervisor if I could conduct research focused on gravitational wave science, but from a particle physics perspective. The main goal of the project was to restrict the existence of so-called lightweight dark matter in our galaxy.”

Light dark matter is a hypothetical candidate for dark matter, consisting of extremely light particles that could solve long-standing mysteries in astrophysics. The latest study conducted by Samara and his colleagues was aimed at verifying the possibility of the presence of this type of dark matter in our galaxy, through data collected by the European Pulsar Timing Array.

“We were inspired by previous efforts in this area, especially by The work of Burayko and her collaborators“Thanks to the longer duration and improved resolution of our data set, we were able to put more stringent constraints on the presence of lightweight dark matter in the Milky Way,” Samara said.

The latest paper by the European Pulsar Timing Array makes different assumptions from those made by other studies conducted in the past. Instead of exploring interactions between dark matter and ordinary matter, it assumes that these interactions occur only through gravitational effects.

“We assumed that dark matter interacts with ordinary matter only through gravitational interaction,” Samara explained. “This is a fairly strong claim: in fact, the only certain thing we know about dark matter is that it interacts with gravity. In short, dark matter produces potential wells in which pulsating radio rays travel. But the depth of these wells is periodic, and so the travel time The radio beam from pulsars to Earth changes with a distinct periodicity as well.

By looking for precisely this effect in the second wave of data from the European Pulsar Timing Array, Samara and his colleagues were able to place new constraints on the presence of very light dark matter around pulsars. The European Pulsar Timing Array has been collecting this data for nearly 25 years, using 6 advanced radio telescopes located in various places around Europe.

“Based on our analyses, we can rule out that ultralight particles in a certain range of masses could make up the entire amount of dark matter,” Samara said. “So, if they were there, we would still need something else to explain what we’re seeing. This result is fairly robust, since we focused on the gravitational interaction of dark matter, which is the only thing we know for sure.”

Recent work by the European Pulsar Timing Array shows that lightweight particles with masses of 10−24.0 eV≲m≲10−23.3 eV cannot make up 100% of the measured local dark matter density and can have a local density of ρ≲0.3 on Most. Jeff/cm³. These new constraints could guide further research in this area, which could benefit future searches for the elusive dark matter candidate.

“I now plan to explore whether pulsars have signatures that can tell us more about dark matter,” Samara added. “Furthermore, I am generally interested in PTA science, so I would also like to work on astrophysical modeling of binary systems of supermassive black holes, which is thought to be a compelling explanation for the random gravitational wave background we recently observed.”