The First RELHIC? Cloud-9 is a Starless Gas Cloud
TL;DR
Imagine the universe is filled with invisible scaffolding made of dark matter - we can't see it directly, but it provides the framework for everything else. Scientists have long predicted that some of these invisible structures should be filled with gas but never light up with stars, like empty lots in a city that have utilities but no buildings. Cloud-9 is the first confirmed example of this phenomenon - it's essentially an "invisible galaxy" made of dark matter and gas, sitting near the spiral galaxy M94. Using powerful telescopes, researchers confirmed it has no stars (making it invisible to normal light) but contains about a million times the mass of our Sun in hydrogen gas. This discovery is important because it proves our theories about how the universe is structured are correct, and helps explain why some cosmic neighborhoods remain dark while others become brilliant galaxies.
Abstract Five-hundred-meter Aperture Spherical Telescope observations have recently identified a compact H i cloud (hereafter Cloud-9) in the vicinity of the spiral galaxy M94. This identification has been confirmed independently by Very Large Array and Green Bank Telescope observations. Cloud-9 has the same recession velocity as M94, and is therefore at a similar distance (∼4.4 Mpc). It is compact ( ∼1′ radius, or ∼1.4 kpc), dynamically cold ( W 50 = 12 km s −1 ), nonrotating, and fairly massive, with an H i mass of ∼10 6 M ⊙ . Here we present deep Hubble Space Telescope/Advanced Camera for Surveys imaging designed to search for a luminous stellar counterpart. We visually rule out the presence of any dwarf galaxy with stellar mass exceeding 10 3.5 M ⊙ . A more robust color–magnitude diagram-based analysis conservatively rules out a 10 4 M ⊙ stellar counterpart with 99.5−8.2+0.5 % confidence. The nondetection of a luminous component reinforces the interpretation that this system is a reionization-limited H i cloud (RELHIC); i.e., a starless dark matter halo filled with hydrostatic gas in thermal equilibrium with the cosmic ultraviolet background. Our results make Cloud-9 the leading RELHIC candidate of any known compact H i cloud. This provides strong support for a cornerstone prediction of the Lambda cold dark matter model, namely the existence of gas-filled starless dark matter halos on subgalactic mass scales, and constrains the present-day threshold halo mass for galaxy formation.
- 1Cloud-9 is confirmed as the first robust candidate for a reionization-limited H i cloud (RELHIC), a starless dark matter halo filled with neutral hydrogen gas
- 2Deep Hubble Space Telescope imaging rules out any stellar counterpart with mass exceeding 10^4 solar masses with 99.5% confidence
- 3The system has properties consistent with theoretical predictions: compact size (~1.4 kpc radius), dynamically cold (W50 = 12 km/s), and massive H i content (~10^6 solar masses)
- 4Cloud-9 provides strong observational support for the Lambda cold dark matter model's prediction of gas-filled starless dark matter halos on subgalactic scales
- 5The discovery constrains the present-day threshold halo mass for galaxy formation at approximately 10^9.7 solar masses
M87's black hole flipped its magnetic field
Imagine a bar magnet with a north and south pole. Now imagine that magnet suddenly flipping so north becomes south and vice versa. That's essentially what happened with the magnetic field around the giant black hole at the center of galaxy M87 — except this black hole is 6.5 billion times heavier than our Sun. Scientists noticed this flip by watching the powerful beam of energy, called a jet, that shoots out from the black hole. The direction and behavior of that beam changed in a way that revealed the magnetic field had reversed. It's a big deal because those magnetic fields are thought to act like the engine that powers and steers these cosmic jets, and we've rarely caught one flipping in action.
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.
Digital twin–guided ablation for ventricular tachycardia
Imagine your heart is a city, and ventricular tachycardia is like a traffic jam caused by a broken road — electrical signals get stuck going in circles instead of flowing properly, causing the heart to beat dangerously fast. Doctors can fix this by burning away the broken road using a procedure called ablation. The problem is, finding the exact broken road inside a beating heart is like navigating a city you've never visited before, while driving, in the dark. What these researchers did is take detailed MRI pictures of each patient's heart, build a 3D computer copy — a 'digital twin' — and then simulate where the electrical problem was happening inside that virtual heart. They tested their fix on the computer model first, figured out exactly where to go, and THEN performed the real procedure. What used to take three hours of exploratory surgery was done in about 30 minutes, because the doctors already had a GPS map before they started.