A type of hydrogen that doesn’t interact with light could explain how long neutrons live and reveal the identity of the universe’s dark matter, according to a new theory.
Category: cosmology – Page 7
Unveiling the birth of star cluster groups in the Milky Way
A study published in Astronomy & Astrophysics has identified four previously unknown primordial open cluster (OC) groups in the Milky Way.
Open clusters, loose assemblies of stars born from the same giant molecular cloud (GMC), are typically considered to form in isolation. However, the newly discovered OC groups consist of multiple member clusters originating from the same GMC, formed through sequential star formation processes.
Notably, two of these groups, labeled G1 and G2, appear to have formed via a hierarchical mechanism triggered by multiple supernova (SN) explosions.
New research determines the thermodynamic properties of the quark gluon plasma
Very soon after the Big Bang, the universe enjoyed a brief phase where quarks and gluons roamed freely, not yet joined up into hadrons such as protons, neutrons and mesons. This state, called a quark-gluon plasma, existed for a brief time until the temperature dropped to about 20 trillion Kelvin, after which this “hadronization” took place.
Now a research group from Italy has presented new calculations of the plasma’s equation of state that show how important the strong force was before the hadrons formed. Their work is published in Physical Review Letters.
The equation of state of quantum chromodynamics (QCD) represents the collective behavior of particles that experience the strong force—a gas of strongly interacting particles at equilibrium, with its numbers and net energy unchanging. It’s analogous to the well-known, simple equation of state of atoms in a gas, PV=nRT, but can’t be so simply summarized.
From infinite past to future: Simulation tracks complete journey of gravitational wave through black hole spacetime
In a new Physical Review Letters study, researchers have successfully followed a gravitational wave’s complete journey from the infinite past to the infinite future as it encounters a black hole.
Reported by scientists from the University of Otago and the University of Canterbury, the study represents the first time anyone has captured the full cause-and-effect relationship of gravitational wave scattering in a single simulation.
The researchers are tackling the scattering problem in gravitational physics. In other words, they want to understand what happens to gravitational waves when they encounter massive objects (like black holes) and scatter off them.
Cosmic ray research helps unravel lithium-7 origin
The origin of lithium (Li), the third element of the periodic table, has long been shrouded in mystery. This element, commonly found in cosmic rays as two stable isotopes, 6 Li and 7 Li, is crucial to understanding the origins of the universe and the evolution of its chemical elements.
In a recent study, an international team of researchers used the Alpha Magnetic Spectrometer (AMS-02) aboard the International Space Station to measure the cosmic-ray fluxes of 6 Li and 7 Li based on data accumulated from May 2011 to October 2023.
Based on information from over 2 million nuclei amassed across 12 years, the team formulated a hypothesis that strengthens the case for one possible origin of lithium while challenging another previously accepted explanation.
Matter-spewing ‘singularities’ could eliminate the need for dark energy and dark matter
“The new model can account for both structure formation and stability, and the key observational properties of the expansion of the universe at large, by enlisting density singularities in time that uniformly affect all space to replace conventional dark matter and dark energy,” research author Richard Lieu, a physics professor at The University of Alabama in Huntsville, said in a statement.
The dark universe is poses such a huge conundrum for scientists because it suggests that only 5% of the matter and energy in the cosmos comprises what we see around us on a day-to-day basis in stars, planets, moons, our bodies — and everything else, really.
In other words, we have no idea what the other 95% of the cosmos is.
Unknown physics may help dark energy act as ‘antigravity’ throughout the universe
The researcher added that with better data on the horizon, including the first public data on galaxy clustering from DESI released last week, the team will re-apply their methods, compare their results with their current findings, and detect any statistically significant differences.
“I think there are more questions than answers at this point,” Chen said. “This research certainly enforces the idea that different cosmological datasets are beginning to be in tension when interpreted within the standard Λ CDM model of cosmology.”
Gravitational-Wave Rockets
Almost every galaxy hosts a supermassive black hole at its center. When galaxies merge, the two black holes spiral in closer to each other and eventually merge through gravitational-wave emission. Within a few billion years, this process will be featured close to home as our own Milky-Way will collide with its nearest massive neighbor, the Andromeda galaxy.
If the two black holes have different masses, the emission of gravitational waves is asymmetric, causing the merger product to recoil. The intense burst of gravitational waves in a preferred direction during the final plunge of the two black holes towards each other, kicks the remnant black hole in the opposite direction through the rocket effect. The end result is that gravitational waves propel the black hole remnant to speeds of up to a few percent of the speed of light. The recoiling black hole behaves like the payload of a rocket powered by gravitational waves.
In 2007, I published a single-authored paper in the prestigious journal Physical Review Letters, suggesting that a gravitational-wave recoil could displace a black hole from the galactic center and endow it with fast motion relative to the background stars. If the kick is modest, dynamical friction on the background gas or stars would eventually return the black hole back to the center.
