Scientists suggest sending atomic clocks near the Sun to search for dark matter

Ultralight dark matter has wavelike properties that could affect the operation of the clocks.
Deena Theresa
Artist's impression of a space atomic clock used to uncover dark matter.
Artist's impression of a space atomic clock used to uncover dark matter.

Kavli IPMU 

For decades, scientists have been trying to wrap their heads around the dark matter, which makes up an estimated 85 percent of the mass in the universe. Despite experimental efforts running for decades, researchers have only been able to observe the essence, not quite detect it.

Now, a new study published in Nature Astronomy on December 5 revealed that an atomic clock on-board a spacecraft inside the inner depths of the solar system could search for ultralight dark matter. The latter has wavelike properties that could affect the operation of the clocks.

Atomic clocks are already in space, enabling Global Positioning Systems (GPS). They tell time by measuring the rapid oscillations of atoms. 

University of Delaware physicist Marianna Safronova and collaborators Yu-Dai Tsai of the University of California, Irvine, and Joshua Eby of the University of Tokyo and the Kavli Institute for the Physics and the Mathematics of the Universe want to put these "precision timepieces to work in the quest to find dark matter," as per a release

Atomic clocks can pick on oscillating signals

According to the researchers, in a particular region of the solar system, between the orbit of Mercury and the Sun, the density of large matter is large. This could translate into exceptional sensitivity to the oscillating signals.

Atomic clocks, which operate by measuring the frequency of photons emitted in transitions of various states in atoms, could pick up these signals. And if there is ultralight dark matter in the presence of the clock experiment, the frequencies will be modified - slightly increasing the oscillations of the dark matter and decreasing the photon energy.

"The more dark matter there is around the experiment, the larger these oscillations are, so the local density of dark matter matters a lot when analyzing the signal," Eby said in a statement.

Different atomic clocks are already working in space

As per the paper, the work would be done by atomic, nuclear, and molecular clocks that are still under development and are known as "quantum sensors."

"This was inspired by the Parker Solar Probe," Safronova said in a statement. The Parker Solar Probe is an ongoing NASA mission that sent a spacecraft closer to the Sun than any other spacecraft has gone before. 

"It showed that you could send a satellite very close to the Sun, sensing new conditions and making discoveries. That is much closer to the Sun than what we are proposing here," she said.

In 2019, NASA's Deep Space Atomic Clock mission demonstrated the best atomic clock in space until now, but Safronova stresses that various types of clocks based on higher frequencies have been developed in the past 15 years. Such clocks will have very precise orders of magnitude and will not even lose a second of time in billions of years.

"There is a whole range of great things we can do in space," Safronova said. "We are at the very, very beginning of that."

Study Abstract:

Recent advances in quantum sensors, including atomic clocks, enable searches for a broad range of dark matter candidates. The question of the dark matter distribution in the Solar system critically affects the reach of dark matter direct detection experiments. Partly motivated by the NASA Deep Space Atomic Clock and the Parker Solar Probe, we show that space quantum sensors present new opportunities for ultralight dark matter searches, especially for dark matter states bound to the Sun. We show that space quantum sensors can probe unexplored parameter space of ultralight dark matter, covering theoretical relaxation targets motivated by naturalness and Higgs mixing. If a two-clock system were able to make measurements on the interior of the solar system, it could probe this highly sensitive region directly and set very strong constraints on the existence of such a bound-state halo in our solar system. We present sensitivity projections for space-based probes of ultralight dark matter, which couples to electron, photon, and gluon fields, based on current and future atomic, molecular, and nuclear clocks.

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