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Category: cosmology

Cosmic ray puzzle resolved as scientists link ‘knee’ formation to black holes

Milestone results released by the Large High Altitude Air Shower Observatory (LHAASO) on November 16 have solved a decades-old mystery about the cosmic ray energy spectrum—which shows a sharp decrease in cosmic rays above 3 PeV, giving it an unusual knee-like shape.

The cause of the “knee” has remained unclear since its discovery nearly 70 years ago. Scientists have speculated that it is linked to the acceleration limit of the astrophysical sources of cosmic rays and reflects the transition of the cosmic ray energy spectrum from one power-law distribution to another.

Now, however, two recent studies—published in National Science Review and Science Bulletin, respectively—demonstrate that micro-quasars driven by black hole system accretion are powerful particle accelerators in the Milky Way and are the likely source of the “knee.” The studies also advance our understanding of the extreme physical processes of black hole systems.

Universe’s expansion ‘is now slowing, not speeding up’: Evidence mounts that dark energy weakens over time

The universe’s expansion may actually have started to slow rather than accelerating at an ever-increasing rate as previously thought, a new study suggests.

“Remarkable” findings published today in Monthly Notices of the Royal Astronomical Society cast doubt on the long-standing theory that a mysterious force known as ‘dark energy’ is driving distant galaxies away increasingly faster.

Instead, they show no evidence of an accelerating universe.

Astronomers Discover Potentially Habitable “Super-Earth” Just 18 Light-Years Away

Astronomers from the University of California, Irvine have discovered a planet orbiting within the “habitable zone” of its host star, a region where temperatures may allow liquid water to exist on the surface. Because water is essential for all known forms of life, this finding raises the possibility that the planet could have life-supporting conditions.

Located in a relatively nearby area of the Milky Way Galaxy, the planet appears to be rocky like Earth but several times more massive, earning it the classification of a “super-Earth.” The team of UC Irvine scientists and their collaborators describe their analysis of the planet in a new paper published in The Astronomical Journal.

“We have found so many exoplanets at this point that discovering a new one is not such a big deal,” said co-author Paul Robertson, UC Irvine associate professor of physics & astronomy. “What makes this especially valuable is that its host star is close by, at just about 18 light-years away. Cosmically speaking, it’s practically next door.”

Black hole mergers could give rise to observable gravitational-wave tails

Black holes, regions of spacetime in which gravity is so strong that nothing can escape, are intriguing and extensively studied cosmological phenomena. Einstein’s general theory of relativity predicts that when two black holes merge, they emit ripples in spacetime known as gravitational waves.

Once the gravitational waves originating from black hole mergers fade, subtle hints of these waves could remain, known as late-time gravitational-wave tails. While the existence of these tails has been widely theorized about in the past, it was not yet conclusively confirmed.

Researchers at Niels Bohr Institute, University of Lisbon and other institutes worldwide recently performed black hole merger simulations based on Einstein’s equations, to further probe the existence of late-time gravitational-wave tails. Their simulations, outlined in a paper in Physical Review Letters, suggest that these tails not only exist, but could also have a larger amplitude than originally predicted and could thus be observed in future experiments.

Our solar system is moving faster than expected

How fast and in which direction is our solar system moving through the universe? This seemingly simple question is one of the key tests of our cosmological understanding. A research team led by astrophysicist Lukas Böhme at Bielefeld University has now found new answers, ones that challenge the established standard model of cosmology.

The study’s findings have just been published in the journal Physical Review Letters.

“Our analysis shows that the solar system is moving more than three times faster than current models predict,” says lead author Böhme. “This result clearly contradicts expectations based on standard cosmology and forces us to reconsider our previous assumptions.”

New evidence suggests Einstein’s cosmic constant may be wrong

Dark energy may be evolving—hinting that the universe’s ultimate destiny could be far stranger than we ever imagined. Astronomers are rethinking one of cosmology’s biggest mysteries: dark energy. New findings show that evolving dark energy models, tied to ultra-light axion particles, may better fit the universe’s expansion history than Einstein’s constant model. The results suggest dark energy’s density could be slowly declining, altering the fate of the cosmos and fueling excitement that we may be witnessing the universe’s next great revelation.

Dark energy, the mysterious force thought to drive the universe’s accelerating expansion, remains one of the deepest puzzles in modern physics. For years, the leading explanation has been that this energy is constant – an unchanging property of empty space responsible for cosmic acceleration. But recent evidence has scientists rethinking that assumption.

Last year, results from the Dark Energy Survey (DES) and the Dark Energy Spectroscopic Instrument (DESI) caught the attention of cosmologists by suggesting that dark energy might not be fixed after all. “This would be our first indication that dark energy is not the cosmological constant introduced by Einstein over 100 years ago but a new, dynamical phenomenon,” explained Josh Frieman, Professor Emeritus of Astronomy and Astrophysics.

Universe’s expansion ‘is now slowing, not speeding up’

The universe’s expansion may actually have started to slow rather than accelerating at an ever-increasing rate as previously thought, a new study suggests.

“Remarkable” findings published today in Monthly Notices of the Royal Astronomical Society cast doubt on the long-standing theory that a mysterious force known as ‘dark energy’ is driving distant galaxies away increasingly faster.

Instead, they show no evidence of an accelerating universe.

A Mathematician’s Model Brings Science Fiction’s Wormholes Closer to Reality

Could a tunnel through space and time—long a dream of science fiction—ever exist in theory? According to Arya Dutta, a Ph.D. student in Mathematics at the Katz School, the answer might be yes, at least on paper.

Accepted for publication in the International Journal of Geometric Methods in Modern Physics, Dutta’s study, “Thin-shell Wormhole with a Background Kalb–Ramond Field,” explored a mathematical model of a wormhole—a hypothetical shortcut through spacetime that could, in theory, connect two distant regions of the universe. “A wormhole allows faster-than-light travel or even time travel,” said Dutta. “It hasn’t been observed yet, but theoretical research has advanced a lot.”

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