Every morning, a janitor sweeps leaves into a pile. The Sun, as it travels through the galaxy, does something similar: its gravity gathers diffuse interstellar gas into an invisible cone — a giant funnel. Every now and then, the James Webb Space Telescope looks into this funnel, and its instruments register a bright flash — the emission line of neutral helium.

This line, with a wavelength of 1.0833 microns (infrared light, invisible to the eye), turned out to be almost ubiquitous. Astronomers analyzed 22 days of observations from the public archive and saw it in 80 percent of all sessions. But the most intriguing part is its variability. In a single day, the line's brightness can change by a factor of several, as if someone is playing with a dimmer switch.

When Webb crosses that gravitational cone, the glow's intensity spikes. Moreover, the calmer the Sun (fewer sunspots and flares), the brighter the line. This suggests that the radiation originates in cold gas of the Milky Way that slowly flows through our system. Previously, such rapid variability, from hours to days, had gone unnoticed.

In essence, Webb has become a tool for studying the interstellar "air" that the Solar System breathes. And this air, it turns out, is far from calm: it flickers and shimmers, responding to solar gravity and activity. Now we have a chance to discern the fine structure of this gas and understand how it mixes with our own "backyard."