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Primordial black holes (PBHs) are black holes formed in the early universe due to extreme density fluctuations, unlike those formed by collapsing stars. Recent research by Banerjee and colleagues explores how radiative symmetry breaking (RSB) , a type of phase transition, might produce PBHs during periods of supercooling. RSB occurs when the universe's temperature drops significantly below a critical level before transitioning to a new phase. This creates unique conditions for forming PBHs. Banerjee's study uses a model-independent approach , meaning their findings apply across many theoretical frameworks. The team discovered that PBHs form in "late-blooming" regions—patches of the universe transitioning later than their surroundings. These PBHs generally have low initial spin and a range of masses, some large enough to survive until today. They also found that PBHs could explain certain microlensing anomalies, suggesting we might have already observed their effects. ...

Black holes are mysterious objects that pull in everything, even light. While black holes with companion stars have been studied a lot, isolated black holes—those wandering alone in space—are harder to understand. A new study by Tripathi and colleagues explores how these black holes interact with streams of gas, or winds, passing by them. When a wind is directly aimed at the black hole, the process follows the classical Bondi-Hoyle-Lyttleton (BHL) model . In this scenario, the wind is pulled straight into the black hole without forming a disk. But when the wind flows past the black hole, a smaller amount of gas is captured, creating a new type of accretion process called lateral BHL accretion . This unique setup can lead to the temporary formation of accretion disks , which are spinning rings of gas orbiting the black hole. The study found that the gas’s composition and temperature affect what happens next. If the gas contains more protons (like electron-proton gas), the disk forms but...

Millicharged particles (mCPs) are a mysterious class of particles with a very small electromagnetic charge, much smaller than that of an electron. These particles are part of the "dark sector" of the universe, which includes invisible particles and forces that don't interact directly with regular matter or light. Despite their tiny charge, mCPs could be produced in large numbers by events like the early universe's Big Bang or stellar processes like supernovae. Detecting these elusive particles is a major challenge because they interact weakly with electromagnetic fields. However, recent advances in light-shining-through-wall (LSW) experiments using superconducting radio-frequency (RF) cavities offer a promising method to detect them. In these experiments, a strong electromagnetic field is created in one cavity, and when mCPs pass through it, they get deflected. This creates small disturbances that can be detected by a nearby shielded cavity. Superconducting RF cavitie...

Axions are hypothetical particles originally proposed to solve a problem in particle physics but have since gained attention as possible dark matter candidates. Dark matter makes up most of the universe's mass, yet we can't detect it directly. Axions are weakly interacting and extremely light, making them ideal candidates. After the Peccei-Quinn (PQ) symmetry breaks in the early universe, axions form "strings" in spacetime called axion strings. These strings move and release energy in the form of axions and gravitational waves (GWs). Recent research by Jia and Bian studied these axion strings and found that they emit more axions than GWs, with the latter being too weak for current detection methods like pulsar timing arrays (PTAs). The study also placed important constraints on axions' mass and decay constant, narrowing down their possible properties. Although the gravitational waves from these strings aren't detectable yet, the research advances our understan...

The question "Are we alone?" has intrigued humans for centuries. As we explore the universe, scientists are searching not only for simple life forms but also for intelligent civilizations, possibly powered by artificial intelligence (AI). This search is part of a field called astrobiology, where researchers aim to find signs of life on exoplanets or detect radio signals from intelligent beings.  A recent proposal by Shant Baghram suggests that advanced civilizations might be powered by AI. Building on the Kardashev scale, which ranks civilizations based on their energy consumption, Baghram argues that AI-dominated civilizations could be between Type II and Type III—using energy from their star and even from black holes.  Baghram also introduces a new concept called space exploration distance, which measures how far a civilization has explored beyond its planet. As these AI civilizations venture further, they may harvest energy from primordial black holes, which are believed t...

In space, particles like ions and electrons are accelerated to extremely high energies in environments such as solar flares, radiation belts, and supernova remnants. The Hillas limit, proposed in 1984, provides a simple way to estimate the maximum energy these particles can achieve. It depends on the magnetic field strength (B), the size of the acceleration region (L), and the particle charge (q). Recent studies confirm that many environments, like supernova remnants, follow the Hillas limit closely. However, exceptions exist. For example, electrons in solar flares and radio galaxies often show much lower energies than predicted. This is likely due to energy losses, like synchrotron radiation, or weak particle confinement. On the other hand, protons in planetary radiation belts sometimes exceed the Hillas limit due to additional energy from processes like cosmic ray interactions. These findings highlight that while the Hillas limit is a useful guideline, factors like energy loss, turbu...

Supernova explosions are some of the most powerful events in the universe, releasing huge amounts of energy. Scientists know they affect the regular matter in galaxies, but what about their impact on dark matter (DM), the mysterious substance that makes up most of the universe’s mass? In the recent study, Vogl and Xu explores how supernova energy could interact with dark matter through a type of invisible energy called  dark radiation . The researchers propose that if even a small fraction of a supernova's energy escapes as dark radiation into the surrounding DM halo, it could alter the halo's shape. Normally, DM halos have a dense “cuspy” center, but the energy from dark radiation might smooth out this center into a less dense “core.” This might explain why some small galaxies, like dwarf galaxies, have cores instead of cusps. To test this idea, the researchers looked at several theoretical models of dark radiation, including particles like dark photons and dark Higgs bosons. ...