Physicists have proposed a mind-boggling space mission that might finally expose the true nature of dark matter, an enigmatic substance that is considered one of the biggest unsolved mysteries in science, reports a new study.
Dark matter is about five times more plentiful in the universe than the familiar stuff that makes up stars, planets, and even our bodies, distinguishing it as a fundamental component of the universe. But despite its abundance, dark matter has proved completely inscrutable to our instruments, and it has never been directly detected; we only know that it exists due to indirect observations of its gravitational influence over luminous bodies, such as galaxy clusters.
Scientists have developed many sophisticated techniques to snag the first direct detection of dark matter, a milestone that could answer a whole host of open questions about our universe, but all have come up short so far.
Now, a team led by Yu-Dai Tsai, a physicist at the University of California, Irvine, has proposed a fascinating space mission that would use the most accurate clocks ever invented to search for dark matter that might be bound to the Sun. In this way, the concept mission, which the team calls SpaceQ, could potentially uncover “new physics” and “study many fundamental physics topics,” according to a study published in Nature Astronomy on Monday.
“Dark matter is one of the most important remaining mysteries in astronomy and cosmology, given its unknown and elusive nature,” Tsai said in an email to Motherboard. “If we could find dark matter and understand its properties, we can understand the evolution of our universe, and understand many astrophysical measurements better, including the velocity distribution of these objects in the small scale (from small galaxies to galaxy clusters).”
“This will also be one of the most significant breakthroughs in particle physics as it is one of the final remaining ingredients to our understanding of particle physics as well,” he added.
The SpaceQ mission concept is built around the incredible accuracy of what the team calls “quantum clocks,” a category that includes existing atomic clocks, which are ultra-precise instruments that use oscillations within atoms to tell time, as well as molecular and nuclear clocks that are currently in development, and are expected to be even more sensitive. In addition to telling time, these clocks can measure incredibly subtle changes in atomic frequencies.
To that end, Tsai started thinking about the possibility of using these clocks to search for a hypothetical version of dark matter, known as ultralight dark matter (ULDM), which theories suggest could become bound to the Sun in a structure called a dark matter halo. A space mission to the Sun might be able to detect ULDM particles, assuming they exist, by measuring tiny changes in the frequencies of the atomic transitions in quantum clocks that expose ULDM’s interactions with other forms of matter.
“We show that the projected sensitivity of space-based clocks for detection of a Sun-bound [dark matter] halo exceeds the reach of Earth-based clocks by orders of magnitude,” Tsai and his colleagues said in the study.
“At present, to our knowledge, this is the only proposal capable of reaching these target sensitivities in our parameter space of interest,” they added.
Since 2020, Tsai has been developing the concept with study co-authors Marianna Safronova, an expert in atomic physics at the University of Delaware, and Joshua Eby, a dark matter expert at the Kavli Institute for the Physics and Mathematics of the Universe.
“The solar probe mission would allow the atomic clocks to study enhanced dark matter density close to the Sun, and probe very interesting and motivated target models detailed in our paper,” Tsai noted. “In addition, we can also test the variation of the fundamental constants, with the change of gravitational potential, when we go close to the Sun. This has been one of the main fundamental physics motivations for developing precise clocks.”
The trio were inspired, in part, by two pioneering NASA missions: the Deep Space Atomic Clock, a test of an unprecedented space navigation clock launched in 2019, and the Parker Solar Probe, which was launched in 2018 and has since traveled closer to the Sun than any other mission. SpaceQ is a dazzling mashup of these two trailblazing missions that combines the Sun-grazing maneuvers of Parker with the sensitive atomic measurements of the deep space clock.
“The Deep Space Atomic Clock (DSAC) is a technology for us to realize space travel, and the Parker Solar Probe is an amazing mission for us to study the Sun,” Tsai said. “Both are existing and cutting-edge technologies with practical purposes. It is amazing to utilize them to study fundamental physics, not to mention the combination of them.”
At this point, the mission is still just an idea, but it offers a novel approach to search for dark matter that could potentially be much more effective than existing techniques. Plus, on a pure gut level, how wild would it be to search for dark matter—one of the biggest missing links in the universe—around our Sun using a daredevil probe carrying ludicrously precise clocks?
“A network of clocks in space and on Earth can study many fundamental physics topics, including transient topological dark matter and multimessenger signatures of exotic particles,” the researchers concluded in the study. “In our consideration, if a signal were to be present, the comparison of ground- and space-based clocks could help to map the density of [dark matter] in the vicinity of Earth to further constrain the bound [dark matter] scenario.”
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