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Category: cosmology

Dark energy might be changing and so is the Universe

Dark energy may be alive and changing, reshaping the cosmos in ways we’re only beginning to uncover. New supercomputer simulations hint that dark energy might be dynamic, not constant, subtly reshaping the Universe’s structure. The findings align with recent DESI observations, offering the strongest evidence yet for an evolving cosmic force.

Since the early 20th century, scientists have gathered convincing evidence that the Universe is expanding — and that this expansion is accelerating. The force responsible for this acceleration is called dark energy, a mysterious property of spacetime thought to push galaxies apart. For decades, the prevailing cosmological model, known as Lambda Cold Dark Matter (ΛCDM), has assumed that dark energy remains constant throughout cosmic history. This simple but powerful assumption has been the foundation of modern cosmology. Yet, it leaves one key question unresolved: what if dark energy changes over time instead of remaining fixed?

Recent observations have started to challenge this long-held view. Data from the Dark Energy Spectroscopic Instrument (DESI) — an advanced project that maps the distribution of galaxies across the Universe — suggests the possibility of a dynamic dark energy (DDE) component. Such a finding would mark a significant shift from the standard ΛCDM model. While this points to a more intricate and evolving cosmic story, it also exposes a major gap in understanding: how a time-dependent dark energy might shape the formation and growth of cosmic structures remains unclear.

ID830 is the most X-ray luminous radio-loud quasar, observations find

An international team of astronomers have employed the Spektr-RG spacecraft and various ground-based telescopes to investigate a distant quasar known as ID830. Results of the new observations, published November 7 on the pre-print server arXiv, indicate that ID830 is the most X-ray luminous radio-loud quasar known to date.

Quasars, or quasi-stellar objects (QSOs), are (AGN) in the centers of active galaxies, powered by supermassive black holes (SMBHs). They showcase very high bolometric luminosities (over one quattuordecillion erg/s), emitting observable in radio, infrared, visible, ultraviolet and X-ray wavelengths.

New Proofs Probe Soap-Film Singularities

It would take nearly a century for mathematicians to prove him right. In the early 1930s, Jesse Douglas and Tibor Radó independently showed that the answer to the “Plateau problem” is yes: For any closed curve (your wire frame) in three-dimensional space, you can always find a minimizing two-dimensional surface (your soap film) that has the same boundary. The proof later earned Douglas the first-ever Fields Medal.

Since then, mathematicians have expanded on the Plateau problem in hopes of learning more about minimizing surfaces. These surfaces appear throughout math and science — in proofs of important conjectures in geometry and topology, in the study of cells and black holes, and even in the design of biomolecules. “They’re very beautiful objects to study,” said Otis Chodosh (opens a new tab) of Stanford University. “Very natural, appealing and intriguing.”

Mathematicians now know that Plateau’s prediction is categorically true up through dimension seven. But in higher dimensions, there’s a caveat: The minimizing surfaces that form might not always be nice and smooth, like the disk or hourglass. Instead, they might fold, pinch or intersect themselves in places, forming what are known as singularities. When minimizing surfaces have singularities, it becomes much harder to understand and work with them.

Black hole blast outshines 10 trillion Suns

A distant supermassive black hole has set a new cosmic record, unleashing the brightest flare ever seen as it devoured a gigantic star that wandered too close. A colossal black hole 10 billion light-years away has been caught devouring one of the universe’s biggest stars, unleashing a flare 30 times brighter than any seen before. The flare, detected by Caltech’s ZTF, likely marks a tidal disruption event — when a star is shredded by a black hole’s gravity.

The Universe’s most massive stars typically end their lives in spectacular explosions known as supernovae before collapsing into black holes. But one enormous star seems to have met a very different fate. Instead of exploding, it strayed too close to an immense black hole, which tore it apart and consumed it piece by piece.

That scenario best explains the findings of a new Nature Astronomy study describing the most powerful and most distant flare of energy ever seen from a supermassive black hole. The object was first detected in 2018 by the Zwicky Transient Facility (ZTF), a sky survey funded by the US National Science Foundation (NSF) and operated at Caltech’s Palomar Observatory. It was also tracked by the Catalina Real-Time Transient Survey, another NSF-funded Caltech project. The flare brightened dramatically — by a factor of 40 within months — and at its peak was 30 times more luminous than any black hole flare observed before. At maximum intensity, it shone with the light of 10 trillion suns.

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.

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