Recently detected gamma rays are best accounted for by relativistic protons accelerated by a millennia-old supernova.
Category: cosmology
Milky Way’s ‘little cousins’ may hold clues about infant universe
Ultra-faint dwarf galaxies—tiny satellite galaxies orbiting the Milky Way—have long been seen as cosmic fossils. Now, a new study published today in Monthly Notices of the Royal Astronomical Society uses an unprecedented set of simulations to show just how powerfully these faint systems can reflect the conditions of the early universe and tell us why some galaxies grew and others did not.
They could also reveal what the universe’s earliest “climate” was like—for example, the level of radiation and how this impacted whether and where stars formed.
Dwarf galaxies are often described as small cousins of the Milky Way. They form in small dark matter halos which are predicted by the standard model of cosmology. The faintest examples of such systems are extreme in both size and fragility, and lie on the boundary of our knowledge about galaxy formation and dark matter.
The Universe Is Accelerating…and No One Knows Why
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REFERENCES
How black holes may be responsible for Dark Energy • How BLACK HOLES May be Responsible for DAR…
Is Dark Energy made of particles? • Is Dark ENERGY made of PARTICLES? The Quin…
What is Dark Energy made of? • What is Dark Energy made of? Quintessence?… CHAPTERS 0:00 The 70% mystery 0:58 How Dark Energy was discovered? 4:26 What could be causing Dark Energy? 6:58 Repulsive Gravity? 10:16 What is the energy made of? 11:56 Evolving Dark energy? Quintesssence 14:18 Could Dark Energy be a particle? 16:43 Could Black Holes cause Dark Energy? SUMMARY Dark energy is one of the greatest mysteries in modern physics. It appears to make up nearly 70% of the universe, yet scientists still do not know what it is. Unlike matter, it does not clump together. Unlike radiation, it does not dilute as space expands. Instead, it causes the expansion of the universe to accelerate, pushing galaxies apart faster over time. The discovery of this acceleration came in the late 1990s when astronomers measured distant Type Ia supernovae, which act as reliable “standard candles.” By comparing their brightness and redshift, researchers could determine how fast the universe expanded at different points in cosmic history. Instead of finding that gravity slowed expansion—as expected—they discovered the opposite: the universe was expanding faster and faster. This unexpected result led to the concept of dark energy, the unknown driver behind cosmic acceleration. One possible explanation is that dark energy is a cosmological constant, represented by the Greek letter lambda in Einstein’s equations. In this model, empty space itself contains a constant energy density known as vacuum energy. Quantum mechanics predicts that empty space is not truly empty; quantum fields constantly fluctuate, producing short-lived “virtual particles.” These fluctuations create energy even in a vacuum. Experiments like the Casimir effect provide evidence that vacuum energy is real. However, this explanation has a major problem. When physicists calculate vacuum energy using quantum theory, the predicted value is about 10¹²⁰ times larger than what observations of the universe allow. This enormous mismatch is widely considered the worst prediction in physics. In general relativity, cosmic acceleration can occur if the universe contains energy with negative pressure. In the Friedmann equation, expansion accelerates when pressure is sufficiently negative relative to energy density. Dark energy appears to have exactly this property, effectively producing a form of repulsive gravity that stretches spacetime. Another possibility is that dark energy is not constant but comes from a dynamic field known as quintessence. In quantum theory, fields can have particle-like excitations, meaning dark energy might correspond to extremely weakly interacting particles. If the strength of this field changes over time, the acceleration of the universe could grow stronger. In extreme scenarios, this could eventually lead to a catastrophic future known as the Big Rip, where galaxies, stars, atoms, and even spacetime itself are torn apart. A more speculative idea suggests a connection between supermassive black holes and dark energy. Some recent studies have observed that black holes appear to grow more massive over billions of years than expected from normal matter accretion alone. Researchers have proposed that black holes might somehow be linked to dark energy, though current evidence only shows a correlation and not a confirmed causal explanation. #darkenergy For now, dark energy remains an observed phenomenon with multiple possible explanations. Whether it is a property of empty space, a new field of physics, or something even deeper, it stands as one of the most profound open questions in cosmology.
CHAPTERS
0:00 The 70% mystery
0:58 How Dark Energy was discovered?
4:26 What could be causing Dark Energy?
6:58 Repulsive Gravity?
10:16 What is the energy made of?
11:56 Evolving Dark energy? Quintesssence
14:18 Could Dark Energy be a particle?
16:43 Could Black Holes cause Dark Energy?
SUMMARY
Dark energy is one of the greatest mysteries in modern physics. It appears to make up nearly 70% of the universe, yet scientists still do not know what it is. Unlike matter, it does not clump together. Unlike radiation, it does not dilute as space expands. Instead, it causes the expansion of the universe to accelerate, pushing galaxies apart faster over time.
The discovery of this acceleration came in the late 1990s when astronomers measured distant Type Ia supernovae, which act as reliable “standard candles.” By comparing their brightness and redshift, researchers could determine how fast the universe expanded at different points in cosmic history. Instead of finding that gravity slowed expansion—as expected—they discovered the opposite: the universe was expanding faster and faster. This unexpected result led to the concept of dark energy, the unknown driver behind cosmic acceleration.
One possible explanation is that dark energy is a cosmological constant, represented by the Greek letter lambda in Einstein’s equations. In this model, empty space itself contains a constant energy density known as vacuum energy. Quantum mechanics predicts that empty space is not truly empty; quantum fields constantly fluctuate, producing short-lived “virtual particles.” These fluctuations create energy even in a vacuum. Experiments like the Casimir effect provide evidence that vacuum energy is real.
Do decoherence, gravity, dark matter and dark energy all originate from quantum corrections?
Only about 5% of the universe is composed of normal matter that we can directly observe, while the remaining 95% is widely believed to consist of dark matter and dark energy. Paradoxically, however, the nature of these dark components remains unknown. Is this due to limitations in our observational capabilities, or does it reflect a more fundamental incompleteness in the classical laws of physics that have long underpinned our understanding of the universe?
In a recent study published in the International Journal of Modern Physics D, I proposed that dark matter and dark energy may not correspond to physically existing substances, but could instead emerge as effective phenomena arising from the quantum nature of gravity.
The Universe Is Expanding Too Fast and Scientists Can’t Explain Why
The most precise measurement yet shows the Universe is expanding faster than expected, deepening the Hubble tension. The result hints that something may be missing from our current understanding of the cosmos.
An international team of astronomers has produced one of the most accurate measurements so far of how quickly the nearby Universe is expanding. Rather than settling a long-standing debate, the new result intensifies one of the biggest unresolved problems in cosmology. The collaboration includes John Blakeslee of NSF NOIRLab, which is funded by the U.S. National Science Foundation, and draws on data from telescopes across two NSF NOIRLab Programs.
Two competing ways to measure cosmic expansion.
Why Quantum Physics Says There’s a Multiverse
In this video.
CHIME tracks a hyperactive repeating fast radio burst source
Using the Canadian Hydrogen Intensity Mapping Experiment (CHIME), an international team of astronomers has performed radio observations of FRB 20220912A—a highly active source of repeating fast radio bursts. Results of the monitoring campaign, published April 10 on the preprint server arXiv, could help us better understand the nature of these enigmatic sources.
Fast radio bursts (FRBs) are intense bursts of radio emission lasting milliseconds showcasing the characteristic dispersion sweep of radio pulsars. The physical nature of these bursts is yet unknown, and astronomers consider a variety of explanations ranging from synchrotron maser emission from young magnetars in supernova remnants to cosmic string cusps.
Our Universe Might Be a Giant Brain, According to New Theories
There’s something quietly unsettling about placing a photograph of a human neuron next to a simulated image of the large-scale cosmic web. The two look almost identical: delicate, branching filaments connecting dense clusters, with vast open spaces in between. One fits inside your skull. The other stretches across billions of light-years. The resemblance is hard to dismiss, and for a growing number of researchers, it’s far more than a visual coincidence.
What started as a striking observation in cosmology and neuroscience has evolved into a serious theoretical question. Could the universe, at its most fundamental level, operate the way a brain does? The ideas being put forward aren’t purely philosophical. Some of them come with testable mathematics, published peer-reviewed papers, and the names of well-regarded physicists attached. What follows is an honest look at where the science currently stands.
The estimated 200 billion detectable galaxies aren’t distributed randomly, but are lumped together by gravity into clusters that form even larger clusters, which are connected to one another by “galactic filaments,” long thin threads of galaxies. This vast architecture is what scientists call the cosmic web. When you zoom far enough out, the structure of the entire observable universe begins to take on a shape that looks startlingly familiar.
Black Hole Jets Pack Power of 10,000 Suns, Stunning New Study Reveals
New observations reveal how black hole jets behave under pressure, offering a crucial benchmark for understanding their role in cosmic evolution.