Cambridge Researchers Uncover Innovative Method for Dark Energy Measurement

In a groundbreaking discovery, researchers hailing from the University of Cambridge have unveiled a novel method for gauging dark energy, the enigmatic force that comprises over two-thirds of the universe and drives its relentless expansion. What's particularly remarkable is that they made this discovery right in our cosmic neighborhood.

Traditionally, scientists have probed dark energy by peering at far-off galaxies, unable to directly perceive this elusive phenomenon. However, the Cambridge team embarked on a unique path. By meticulously examining the mutual gravitational dance of Andromeda and our own Milky Way, they were able to establish an upper limit on the cosmological constant, which represents the simplest model of dark energy. Astonishingly, this upper limit exceeded the values previously discerned from the early universe by a factor of five.

Although this technique is still in its infancy, the implications are profound. It suggests that we might eventually detect dark energy by scrutinizing our immediate cosmic surroundings. These findings have been published in The Astrophysical Journal Letters.

In our observable cosmos, everything, from the tiniest insects to colossal galaxies, constitutes a mere five percent. The remaining 95 percent remains shrouded in darkness: approximately 27% is believed to be dark matter, the binding force of the cosmos, while a staggering 68% is attributed to dark energy, the cosmic push that propels celestial objects away from each other.

Dr. David Benisty, the first author from the Department of Applied Mathematics and Theoretical Physics, explains, "Dark energy is a general term encompassing various models that could supplement Einstein's theory of gravity. The simplest of these is known as the cosmological constant, a constant energy density that propels galaxies apart."

Einstein initially introduced the cosmological constant into his theory of general relativity but later discarded it. It remained dormant until the late 1990s when scientists uncovered dark energy's role in the universe's accelerated expansion. However, the challenges persist: the exact nature of dark energy remains elusive, and direct detection remains elusive.

Over the years, astronomers have devised several methods to detect dark energy, primarily involving the study of objects from the universe's infancy and assessing their rate of recession. However, parsing the effects of dark energy from eons past proves challenging, as the force is overshadowed by the more potent gravitational forces at play within galaxies.

Yet, remarkably, there exists a region within the universe acutely sensitive to dark energy, and it happens to be right in our cosmic backyard. The Andromeda galaxy, the closest neighbor to our Milky Way, is on a collision course with us. As these galaxies draw near, they will commence a slow cosmic waltz, with a single orbit consuming a staggering 20 billion years. However, due to the overwhelming gravitational forces, they will merge and collide roughly five billion years from now.

Dr. Benisty underscores, "Andromeda is the lone galaxy not receding from us, allowing us to study its mass and movement for insights into the cosmological constant and dark energy."

By running simulations founded on the best available mass estimates for both galaxies, Benisty and his colleagues, Professor Anne Davis and Professor Wyn Evans, discovered that dark energy significantly influences how Andromeda and the Milky Way orbit one another.

Benisty elucidates, "Dark energy exerts its influence on every pair of galaxies: gravity endeavors to bring them together, while dark energy compels them apart. In our model, by altering the value of the cosmological constant, we can observe how it alters the galaxies' orbital patterns. Based on their mass, we can establish an upper boundary for the cosmological constant, one five times greater than what we can measure from the rest of the universe."

The researchers acknowledge that while this technique shows immense promise, it isn't a direct detection of dark energy. More precise measurements of Andromeda's mass and motion from the James Webb Telescope (JWST) could potentially refine these upper limits on the cosmological constant.

Furthermore, studying other pairs of galaxies may further fine-tune the technique and provide deeper insights into how dark energy shapes our universe. "Dark energy remains one of cosmology's greatest enigmas," remarks Benisty. "It's possible that its effects fluctuate across distances and epochs, but we hope that this technique can help unravel the mystery."

For those interested, the research paper titled "Constraining Dark Energy from the Local Group Dynamics" by David Benisty, Anne-Christine Davis, and N. Wyn Evans was published on August 8, 2023, in The Astrophysical Journal Letters.