Scientists help detect dark energy by testing gravity

Scientists help detect dark energy by testing gravity

This image, the first released by NASA’s James Webb Space Telescope, shows galaxy cluster SMACS 0723. Some galaxies appear to be smeared or stretched due to a phenomenon called gravitational lensing. This effect could help scientists map the presence of dark matter in the universe. Image credits: NASA, ESA, CSA, STScI

Could one of the biggest puzzles in astrophysics be solved by revamping Einstein’s theory of gravity? A new study co-authored by NASA scientists suggests not yet.

The expansion of the universe is accelerating, and scientists don’t know why. This phenomenon seems to contradict everything researchers understand about the effects of gravity on the universe: It’s as if you throw an apple into the air, and it keeps going up, faster and faster. The cause of the acceleration, known as dark energy, remains a mystery.

A new study from the International Dark Energy Survey, using the Victor M. Blanco 4-meter telescope in Chile, marks the latest effort to determine if this is just a misunderstanding: the understanding of how gravity works on a cosmic scale Expectations are defective or incomplete. This potential misunderstanding may help scientists explain dark energy. But the study — one of the most precise tests yet of Albert Einstein’s theory of cosmic-scale gravity — found that the current understanding still appears to be correct.

Findings presented by a team of scientists, including some at NASA’s Jet Propulsion Laboratory, at the International Conference on Particle Physics and Cosmology (COSMO’22) in Rio de Janeiro on Wednesday, Aug. 23. The work lays the groundwork for two upcoming space telescopes that will explore our understanding of gravity with greater precision than the new study and may finally solve the mystery.

More than a century ago, Albert Einstein developed general relativity to describe gravity, and it has so far accurately predicted everything from the orbit of Mercury to the existence of black holes. But if the theory doesn’t explain dark energy, some scientists believe, then they may need to revise some of its equations or add new components.

To find out if this is the case, members of the Dark Energy Survey looked for evidence that the strength of gravity has changed over cosmic history or cosmic distances. A positive finding that suggests Einstein’s theory is incomplete could help explain the accelerated expansion of the universe. They also examined data from other telescopes besides Blanco, including the ESA (European Space Agency) Planck satellite, and came to the same conclusion.

The video explains a phenomenon called gravitational lensing, which causes images of galaxies to appear distorted or blurred. This twist is caused by gravity, an effect scientists can use to detect dark matter that doesn’t emit or reflect light.Image credit: NASA Goddard Space Flight Center

The study found that Einstein’s theory was still valid. So there is no explanation for dark energy yet. But the research will be used for two upcoming missions: the Euclid mission, scheduled to launch no earlier than 2023, provided by NASA; and NASA’s Nancy Grace Roman Space Telescope, targeted for 2027 Launch before May. Both telescopes will search for changes in gravitational strength over time or distance.

blurred vision

How do scientists know what happened to the universe in the past? By looking at distant objects. A light-year is a measure of the distance light can travel in a year (about 6 trillion miles, or about 9.5 trillion kilometers). This means that an object one light-year away appears to us as it did a year ago when light first left the object. Galaxies billions of light-years away appear to us as they did billions of years ago. The new study looked at galaxies around 5 billion years ago. Euclid will look back 8 billion years and Roman will look back 11 billion years.

Galaxies themselves don’t reveal the strength of gravity, but what they look like from Earth does. Most matter in our universe is dark matter, which does not emit, reflect or otherwise interact with light. While scientists don’t know what it’s made of, they know it’s there because its gravity exposes it: the vast reservoir of dark matter in our universe warps space itself. As light travels through space, it encounters these distorted parts of space, causing images of distant galaxies to appear curved or blurred. This is one of the first images released by NASA’s James Webb Space Telescope.

Dark Energy Survey scientists search images of galaxies for more subtle distortions caused by dark matter bending space, an effect called weak gravitational lensing. The strength of gravity determines the size and distribution of dark matter structures, which in turn determine how distorted these galaxies are to us. This is how images reveal the strength of gravity at different distances from Earth and in distant times throughout the history of the universe. The team has now measured the shape of more than 100 million galaxies, and so far, the observations match the predictions of Einstein’s theory.

“As measurements become more precise, there is still room for challenges in Einstein’s theory of gravity,” said study co-author Agnès Ferté, a postdoctoral researcher at JPL. “But we still have a lot of work to do before we’re ready for Euclid and Rome. So we must continue to work with scientists around the world to solve this problem, as we have done in dark energy investigations That way.”

NASA’s Rome mission will test competing theories of cosmic acceleration

More information:
Dark Energy Survey Year 3 Results: Constraints on ΛCDM Extensions with Weak Lensing and Galactic Clusters, arXiv:2207.05766 [astro-ph.CO]

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