absorption line

The Andromeda galaxy is our nearest large neighbor, and like the Milky Way, it has an invisible gaseous shroud. This shroud of extremely hot, rarefied gas extends for hundreds of thousands of light-years. Seeing it directly is nearly impossible — the gas is too faint.

Imagine a huge stadium packed with people dressed in black. You're standing outside, trying to figure out what's happening inside, even though you can't see a single person. But if two people bump into each other and exchange bright T-shirts, you'd spot a flash of color.

The cosmic detective story began with a quiet flash in the optical band. AT2019wzc slowly brightened and faded like a smoldering ember. But hidden inside was something more energetic — repeating soft X-ray bursts that astronomers call quasi-periodic eruptions. These eruptions last minutes to hours and repeat every few hours or days.

A bright lantern in thick fog seems dim, while a weak flame in clear air can be seen a kilometer away. A similar oddity baffled astrophysicists almost half a century ago.

Forty reddish sparks frozen in the images from JWST. The telescope spotted them in the depths of space, at distances where the Universe was less than two billion years old. These objects are active galactic nuclei — very compact and unusually red. Their color earned them the nickname 'little red dots' (LRDs).

A billiard ball slams into another. Impact, and the balls scatter. But if the push is not sharp but very gentle, the balls just roll together without bouncing. An atom behaves much the same way when hit by a dark matter particle.

The James Webb Space Telescope peered into the era when the expansion of the Universe stretched the light of distant objects into the red, and found a scattering of strange sources — 'little red dots'. Their spectra broke the usual patterns: they are blue in the ultraviolet, but deep red in the optical, as if seen through a cherry veil.

The cosmic microwave background is the afterglow of the Big Bang, which we see at millimeter wavelengths. But it also has a long-wavelength tail extending into the radio range.

Every galaxy floats in an invisible cloud of gas, like fruit in syrup. This gas is the leftover building material from which stars were assembled, and it is constantly replenished by fresh supplies from intergalactic space. Seeing it directly is nearly impossible: it is too tenuous and too cold.

At the center of galaxy PDS 456 shines a quasar — a black hole devouring gas that glows brighter than hundreds of billions of stars. The X-ray telescope XRISM peered into this light and saw a picket fence of dark bands, like shadows cast by a fence at sunset.

A giant magnifying glass made of gravity zoomed in on a distant galaxy, and astronomers got a peek into its chemical kitchen.

A gamma-ray spectrum looks like a picket fence: each line is the precise energy a nucleus released as a photon. But sometimes ghosts appear in that fence — faint lines shifted by the same amount from the main ones. Such a shift could mean that part of the energy went into creating a light particle we cannot yet see directly.

Gas is nearly invisible, but it has a temperature, and you can read it from how the gas 'shadows' the thermal background. In the experiment, a camera looks at a warm screen through a jet of carbon dioxide. If the gas is cooler than the background, it appears as a dark spot; if warmer, it appears bright.

A distant galaxy birthing hundreds of stars should glow in oxygen. That's what astronomers thought: hot young stars heat the gas, which then emits a characteristic infrared glow at a wavelength of 63 microns. It's like steam rising from a boiling pot — a sure sign of vigorous activity.

A distant red object usually means one thing: we're seeing a dust veil over a scorching disk falling into a black hole. But when the James Webb split its light into shades, a shadow appeared inside — just like steam from boiling water intercepts rays.

An ordinary laser amplifies light into a bright beam. Run the process in reverse, and you get an anti-laser — a device that sucks in light without a trace. But such a machine is finicky: even a slight disorder can ruin the absorption. Physicists have found a way to make the anti-laser invulnerable.