The search for dark matter and dark energy widens

The hunt for dark matter and dark energy in the universe is expanding.

The big picture: Gravity from dark matter holds gas and dust together in stars and galaxies while dark energy pushes galaxies away from one another. Together, scientists think they make up 95 percent of our universe but what exactly they are remains elusive.

• Over decades, a few dark matter candidates have been crossed off the list (it's not any of the known elementary particles) and scientists have discovered new galaxies and places to search for clues about both dark energy and dark matter.
• "The indirect observations of dark matter just continue to grow," Joseph Pesce, program director at the National Science Foundation tells Axios. "We see dark matter kind of everywhere we look, and it seems to follow matter."

Now, the next generation of tools to spot evidence of dark matter and dark energy is coming online, adding more precise space-based telescopes and new ground observatories to the hunt.

• "We desperately need data to tell us how to build our theories and to refine them, and to tell us which ones are right, which ones have a chance of being right, and which ones are just wrong," says Timothy Tait, a particle physicist at the University of California, Irvine.

Driving the news: The European Space Agency's Euclid space telescope is slated to launch from Cape Canaveral on July 1 aboard a SpaceX Falcon 9 rocket. (The telescope was originally meant to fly on a Russian Soyuz rocket, but ESA made the switch after Russia invaded Ukraine.)

• It will survey more than one-third of the sky — collecting data from 1 billion galaxies that existed as far back as when the universe was a mere 3.8 billion years old.
• Gravity from dark matter still dominated the universe then and slowed its expansion until about 7 billion years ago, when dark energy's influence became greater and the universe began to expand more rapidly. Its effects can be seen in the radiation left over from the Big Bang and how fast galaxies recede into space over time.
• Euclid will capture images of galaxies and other objects during that transition, which scientists hope will yield new clues.

How it works: The images gathered by Euclid will be used to determine the size of the universe at various points in time.

• Light from galaxies can be distorted by clumps of dark matter as it travels across the universe. From that data, scientists can create a map of dark matter in the universe at different times. What that distortion looks like can also help scientists determine if dark matter is made of heavy or light particles — information that can help to hone the search for dark matter candidates in particle accelerators on Earth.
• Data from Euclid images will also be used to look at how the distances between clusters of galaxies changed over the history of the universe as they were influenced by dark energy.
• "The underlying landscape of how big the universe is and how quickly it's growing, and the gravity that's pulling structures together interplay with each other," says Leonidas Moustakas, an observational cosmologist at NASA's Jet Propulsion Laboratory who is a member of the Euclid science team. "If you can measure statistically the amount of structure at different times, you can connect it to the size of the universe."

Between the lines: Ultimately answers about dark energy will determine whether the acceleration of the universe can be explained by a mathematical fix to Einstein's theory of gravity known as the cosmological constant, an entirely new force or a modification of theories of gravity.

What to watch: NASA is planning to launch its Nancy Grace Roman space telescope in 2027, which will also study cosmic acceleration using some of the same methods as Euclid.

• It will survey a smaller area of the sky — overlapping with Euclid — but with greater precision.
• The ground-based Vera Rubin Observatory, which is expected to begin operations in the next year, will also probe the nature of dark matter by picking up the distorted light emitted by distant objects and warped by other, closer objects to see how much dark matter's unseen gravity is influencing our universe.

The very big picture: "We're very lucky that we live in this cosmic epoch," Tait says.

• Any earlier in the universe, dark energy would have such a small effect that its effects wouldn't be measurable, he says. And, if we lived far in the future, dark energy would dominate everything.
• We're in the midst of a relatively balanced cosmic push and pull between dark energy and dark matter.
• That gives scientists the opportunity to measure both but also to explore whether they might interact and whether one is determining the properties of the other, Tait says.
• "If that's true, then it's only in a time like now where you can see kind of similar amounts of both of them, that you would be able to see those dynamics and actually understand that important piece of the puzzle."