The blazar BL Lacertae, a supermassive black hole surrounded by a bright disk and jets oriented toward Earth, provided scientists with a unique opportunity to answer a longstanding question: How are X-rays generated in extreme environments like this?
NASA’s IXPE (Imaging X-ray Polarimetry Explorer) collaborated with radio and optical telescopes to find answers. The results, available on the arXiv preprint server and set to be published in the journal Astrophysical Journal Letters, show that interactions between fast-moving electrons and particles of light, called photons, must lead to this X-ray emission.
Scientists had two competing possible explanations for the X-rays, one involving protons and one involving electrons. Each of these mechanisms would have a different signature in the polarization of X-ray light. Polarization is a property of light that describes the average direction of the electromagnetic waves that make up light.
What is time? Speaking time travel, black holes and the remits of science. In this podcast conversation, we speak with Professor David Wilkinson — physicist and author of popular science books on Stephen Hawking to explore the question: can we ever fully understand time through science, or does it open up more mystery?
How do you distinguish a galaxy from a mere cluster of stars? That’s easy, right? A galaxy is a large collection of millions or billion of stars, while a star cluster only has a thousand or so. Well, that kind of thinking won’t get you a Ph.D. in astronomy! Seriously, though, the line between galaxy and star cluster isn’t always clear. Case in point, UMa3/U1.
It’s easy to distinguish galaxies such as Andromeda and the Milky Way. They are large, gravitationally bound, and dominated by dark matter. It’s also easy to distinguish star clusters such as the Pleiades. They are loosely bound star groupings without dark matter. But for a type of small dwarf galaxy known as Ultra-Faint Dwarfs (UFDs) the dividing line gets fuzzy.
UFDs are dominated by dark matter. The mass of the Milky Way, for example, is about 85% dark matter. An ultrafaint dwarf galaxy, however, can have a thousand times more dark matter than luminous matter. This is why they are so faint. Since UFDs often contain some of the oldest stars in the Universe, astronomers love to study them for clues on the origins of galaxies. Which brings us to UMa3/U1.
Ever since general relativity pointed to the existence of black holes, the scientific community has been wary of one peculiar feature: the singularity at the center—a point, hidden behind the event horizon, where the laws of physics that govern the rest of the universe appear to break down completely. For some time now, researchers have been working on alternative models that are free of singularities.
A new paper published in the Journal of Cosmology and Astroparticle Physics, the outcome of work carried out at the Institute for Fundamental Physics of the Universe (IFPU) in Trieste, reviews the state of the art in this area. It describes two alternative models, proposes observational tests, and explores how this line of research could also contribute to the development of a theory of quantum gravity.
“Hic sunt leones,” remarks Stefano Liberati, one of the authors of the paper and director of IFPU. The phrase refers to the hypothetical singularity predicted at the center of standard black holes —those described by solutions to Einstein’s field equations. To understand what this means, a brief historical recap is helpful.
NGC 4945, a beautiful spiral galaxy over 12 million light-years away, hides a ferocious secret: a ravenous black hole at its center. This supermassive beast doesn’t just consume matter — it blasts it back out at incredible speeds, launching winds that escape the galaxy itself. This featured Eu
In 2024 a shockwave rippled through the astronomical world, shaking it to the core. The disturbance didn’t come from some astral disaster at the solar system’s doorstep, however. Rather it arrived via the careful analysis of many far-distant galaxies, which revealed new details of the universe’s evolution across eons of cosmic history. Against most experts’ expectations, the result suggested that dark energy —the mysterious force driving the universe’s accelerating expansion—was not an unwavering constant but rather a more fickle beast that was weakening over time.
The shocking claim’s source was the Dark Energy Spectroscopic Instrument (DESI), run by an international collaboration at Kitt Peak National Observatory in Arizona. And it was so surprising because cosmologists’ best explanations for the universe’s observed large-scale structure have long assumed that dark energy is a simple, steady thing. But as Joshua Frieman, a physicist at the University of Chicago, says: “We tend to stick with the simplest theory that works—until it doesn’t.” Heady with delight and confusion, theorists began scrambling to explain DESI’s findings and resurfaced old, more complex ideas shelved decades ago.
In March 2025 even more evidence accrued in favor of dark energy’s dynamic nature in DESI’s latest data release—this time from a much larger, multimillion-galaxy sample. Dark energy’s implied fading, it seemed, was refusing to fade away.
A colossal structure in the distant Universe is defying our understanding of how the Universe evolved.
In light that has traveled for 6.9 billion years to reach us, astronomers have found a giant, almost perfect ring of galaxies, some 1.3 billion light-years in diameter. It doesn’t match any known structure or formation mechanism.
The Big Ring, as the structure has been named, could mean that we need to amend the standard model of cosmology.
Two independent teams have searched for axions using x-ray observations of entire galaxies, setting some of the strictest constraints to date on the properties of these dark matter candidates.
