Turbocharging constraints on dark matter substructure through a synthesis of strong lensing flux ratios and extended lensed arcs
TL;DR
Imagine you're looking at a distant flashlight through a glass marble — the marble bends the light and creates multiple distorted images of the flashlight. Now imagine tiny invisible lumps scattered around the marble. Those lumps would subtly warp the images in ways we can measure. That's gravitational lensing! Dark matter forms these invisible lumps (called subhalos), and different theories of what dark matter IS predict different sizes and numbers of these lumps. This paper combines two ways of studying those warped images — the brightness of the multiple images AND the smeared arc of light from the galaxy around the flashlight — to get a much sharper picture of those tiny lumps. They also built a mathematical shortcut that makes the calculations 100 to 1000 times faster. The upshot: they can now test whether dark matter clumps exist down to sizes smaller than has ever been probed before, helping us rule out certain types of dark matter particles.
Strong gravitational lensing provides a purely gravitational means to infer properties of dark matter halos and thereby constrain the particle nature of dark matter. Strong lenses sometimes appear as four lensed images of a background quasar accompanied by spatially-resolved emission from the quasar host galaxy encircling the main deflector (lensed arcs). We present methodology to simultaneously reconstruct lensed arcs and relative image magnifications (flux ratios) in the presence of full populations of subhalos and line-of-sight halos. To this end, we develop a new approach for multi-plane ray tracing that accelerates lens mass and source light reconstruction by factors of $\sim 100-1000$. Using simulated data, we show that simultaneous reconstruction of lensed arcs and flux ratios isolates small-scale perturbations to flux ratios by dark matter substructure from uncertainties associated with the main deflector mass profile on larger angular scales. Relative to analyses that use only image positions and flux ratios to constrain the lens model, incorporating arcs strengthens likelihood ratios penalizing warm dark matter (WDM) with a suppression scale $m_{\rm{hm}} / M_{\odot}$ in the range $\left[10^7 - 10^{7.5}\right]$, $\left[10^{7.5} - 10^{8}\right]$, $\left[10^8 - 10^{8.5}\right]$, $\left[10^{8.5} - 10^{9}\right]$ by factors of $1.3$, $2.5$, $5.6$, and $13.1$, respectively, for a cold dark matter (CDM) ground truth. The $95\%$ exclusion limit improves by 0.5 dex in $\log_{10} m_{\rm{hm}}$. The enhanced sensitivity to low-mass halos enabled by these methods pushes the observational frontier of substructure lensing to the threshold of galaxy formation, enabling stringent tests of any theory that alters the properties of dark matter halos.
- 1A new methodology is presented for simultaneously reconstructing lensed arcs and flux ratios in the presence of full populations of subhalos and line-of-sight halos.
- 2A new multi-plane ray tracing approach accelerates lens mass and source light reconstruction by factors of ~100-1000.
- 3Combining lensed arcs with flux ratios isolates small-scale dark matter substructure perturbations from main deflector mass profile uncertainties on larger angular scales.
- 4Incorporating arcs strengthens likelihood ratios penalizing warm dark matter by factors of 1.3, 2.5, 5.6, and 13.1 across successive half-decade bins in halo mass suppression scale.
- 5The 95% exclusion limit on the warm dark matter halo mass suppression scale improves by 0.5 dex, pushing substructure lensing to the threshold of galaxy formation.
The 2026 World Cup's grass is an engineering problem
Imagine you're trying to play soccer in 16 different places across the United States, Canada, and Mexico — some in freezing cold, some blazing hot, some in stadiums with roofs that block sunlight. Half of those stadiums normally use fake grass. Now FIFA, the organization that runs the World Cup, wants every single pitch to feel and play exactly the same way, like a video game where every level has identical physics. To do that, they hired grass scientists — yes, that's a real job — who figured out how to grow special grass on thin mats with plastic underneath so it can be transported like a carpet, stitched with synthetic fibers so it doesn't rip when players sprint and tackle, and tested by literally shooting balls at it with a cannon to make sure it bounces right. Different grass species are used depending on whether a stadium is hot, cool, or dark. It's basically a giant, living, high-tech floor installation that has to survive the world's best athletes running on it.
Non-Mendelian inheritance of DNA methylation patterns in mice
Imagine your DNA is like a huge book of instructions. Mendel's laws are the normal rules for how chapters of that book get passed from parents to children. But there's also a layer of sticky notes on top of the book—called epigenetic marks—that tell cells which chapters to read and which to ignore. This study found that most of the time (about 93%), these sticky notes follow the normal inheritance rules. But about 7% of the time, they do something unexpected: new patterns appear that neither parent had, or a mark from one parent somehow silences the same mark from the other parent (called paramutation), or males and females end up with completely different sticky notes even when they inherit the same DNA. Scientists discovered this by using a new ultra-precise DNA reading technology in mice, and it opens the door to understanding hidden layers of how traits—and possibly diseases—are passed down through generations.
Adversarial AI reveals mechanisms and treatments for disorders of consciousness
Imagine your brain is like a city with millions of roads and traffic systems. When you're awake and conscious, traffic flows in complex, coordinated patterns. In a coma, something has gone wrong — but we've never had a great way to figure out exactly which roads are broken or how to fix them. This study built a very smart AI that learned to tell the difference between 'awake brain' and 'coma brain' by studying hundreds of thousands of brainwave recordings. Then, like a detective, the AI was pitted against a simulated model of the brain to figure out: what changes in the brain's wiring would explain the difference? The AI figured out — on its own, without being told — that two key things go wrong in a coma: a specific circuit deep in the brain (called the basal ganglia indirect pathway) gets disrupted, and the brain's 'braking system' (inhibitory neurons) starts working too hard in the wrong places. The researchers then checked these predictions against real patient data, and both checked out. The AI also suggested that zapping a specific deep brain region with high-frequency electrical pulses might help wake people up — and early evidence from human patients supports this idea.
Trionda: Enhanced Surface Roughness Relative to Previous FIFA World Cup Match Balls
Imagine throwing a ball through air. The air pushes back on the ball, slowing it down—that's called drag. But something interesting happens: at a certain speed, the air flowing around the ball switches from a smooth, lazy flow to a chaotic, turbulent flow, and paradoxically the ball actually experiences LESS drag in that turbulent zone. Think of it like a golf ball—those dimples are there precisely to trigger this turbulence early and make the ball fly farther. The speed at which this switch happens is called the 'critical speed' or 'drag crisis.' Scientists put the Trionda ball in a wind tunnel—basically a giant fan tube—and measured exactly how much air resistance it faces at different speeds. They found that Trionda's surface is effectively rougher than most previous World Cup balls, meaning it hits that drag crisis switch at a lower speed (11.9 meters per second, roughly 27 mph). In plain terms, Trionda behaves more predictably in flight than some past balls, but very long, powerful kicks may travel slightly shorter distances than they would have with previous balls.