New work brings researchers closer to understanding dark matter. [Image: Witthaya Prasongsin/ Getty Images]
For half a century or more, astronomers have searched the universe for clues to the nature of dark matter: a hypothetical type of matter that does not interact with electromagnetic radiation. With light detectors off the table, scientists must use unconventional technologies to seek evidence of dark matter’s existence.
Researchers in Australia and Germany have developed a new technique that searches for subtle interactions between potential dark matter and electrons (Phys. Rev. Lett., doi: 10.1103/PhysRevLett.134.031001 ). The team analyzed data from a network of cavity-stabilized lasers connected by optical fiber, as well as data from atomic clocks aboard GPS satellites. The comparison yielded new constraints on the effects that hypothetical dark matter may have on electrons.
Dark matter in the cosmos
The search for dark matter originated decades ago, when scientists realized that their optical and radio-frequency observations of the motions of galaxies did not square with their calculations of the amount of mass in these galaxies. The “missing mass” quickly became one of the great unsolved mysteries in astronomy. To track down its nature, astrophysicists have looked for possible interactions between these tiny hypothetical dark particles and known subatomic particles, or at how dark matter affects the values of fundamental physical constants.
The researchers at the University of Queensland, Australia, and the Physikalisch-Technische Bundesanstalt (PTB), Germany, looked for oscillations in the frequency ratio between two spatially separated lasers connected by a 2200-km-long optical fiber. PTB and British scientists had originally developed the setup used for this experiment to improve the performance of optical clocks. The two lasers were stabilized to an optical cavity, so that any changes in the length of the cavity would alter the frequency of the lasers—and scientists can easily measure such small changes in laser frequency.
The search for dark matter originated decades ago, when scientists realized that their optical and radio-frequency observations of the motions of galaxies did not square with their calculations of the amount of mass in these galaxies.
Space and time results
Since the lasers were separated by both space and time, researchers were able to filter out the parts of the signal between the two lasers that were caused by the time separation. On the other hand, the spatial separation’s effects—with the dark matter assumed to be a bosonic field acting like coherent waves—could have revealed the presence of dark matter particles. However, the team found no statistically significant oscillations in the signal.
In the other test of the dark matter hypothesis, the Queensland–PTB group also studied the rubidium-based microwave atomic clocks aboard multiple GPS satellites, which are compared with a ground-based hydrogen maser. Combined with the laser-pair results, the researchers came up with a number representing the coupling of scalar dark matter to elections for masses between 10–19 and 2 × 10–15 eV/ c2.