Welcome back, and thanks for spending another evening here. Tonight we have thirteen stops, from stars that keep records of their own orbits to a visitor that may be older than the Sun.
We'll watch two stars draw rings of dust, meet a dead star barely larger than the Moon, find enormous circles that only radio telescopes can see, and visit a moon that another world is slowly painting red. At the end, we'll follow a comet that has been travelling far longer than our Solar System has existed.
Get comfortable. 🌙
1. ⭐ Wolf-Rayet 140 draws dust rings like a fingerprint
In 2022, the James Webb Space Telescope photographed a star system surrounded by at least 17 concentric rings, like the ridges of an enormous fingerprint.
Wolf-Rayet 140 contains two massive stars on an elongated orbit that lasts about eight years. One is a Wolf-Rayet star, hot and evolved, blowing an extremely powerful wind. The other is a massive O-type star.
When the stars swing close together, their winds collide and compress carbon-rich gas enough for dust to form. As they separate again, that fresh dust drifts outward as a new shell. Webb's images show the result of more than a century of orbits.
Comparing observations taken a year apart, astronomers have even watched the shells expand, moving outward at close to 1% of the speed of light.
The system is building its own tree rings: a new shell of dust for every orbit, each one recording time as it drifts away.
2. ⭐ ZTF J1901+1458 is a white dwarf barely larger than the Moon
White dwarfs are what stars like the Sun leave behind when they finish fusing. Most are roughly the size of Earth.
ZTF J1901+1458 is only about 4,300 kilometers across, scarcely larger than our Moon. Yet it holds around 1.35 times the Sun's mass, close to the theoretical limit for a white dwarf.
It also spins once every seven minutes and has an extremely strong magnetic field. Together, those clues suggest it formed when two smaller white dwarfs merged. Mergers like this can sometimes trigger a thermonuclear supernova, but this one apparently survived.
Some researchers have suggested it might eventually collapse into a neutron star, although that remains speculative.
Two dead stars may have combined into one that packs more than the Sun's mass into something barely bigger than the Moon.
3. ⭐ Epsilon Aurigae's eclipses last nearly two years
Every 27 years, the bright star Epsilon Aurigae fades, and then stays dim for an astonishingly long time. Each eclipse lasts nearly two years.
For more than a century, astronomers struggled to explain what could block a star for so long.
The leading explanation is a companion star wrapped in a vast disk of dust and gas. As the companion moves along its orbit, the disk slowly passes in front of the brighter star, and it's so large that crossing takes years. Infrared observations from the Spitzer Space Telescope helped measure the disk and support this picture.
What passes in front of the bright star isn't another star at all, but a comparatively cool sheet of material much larger than the companion it surrounds.
An eclipse can outlast some spacecraft missions when the thing doing the eclipsing is an entire disk around a star.
4. 🕳️ GW200105 and GW200115 caught black holes swallowing neutron stars
Gravitational-wave observatories had already detected black holes merging with black holes, and neutron stars merging with neutron stars. A black hole merging with a neutron star remained elusive.
In January 2020, they recorded two such events, ten days apart: GW200105 and GW200115.
In one, a black hole of roughly 8.9 solar masses merged with a neutron star of about 1.9. In the other, a black hole of about 5.7 solar masses merged with a neutron star of about 1.5. The detections were announced in June 2021.
Neither produced a confirmed flash of light. Depending on the masses, spins and orbit, a black hole can swallow a neutron star whole without tearing off enough material to make a bright display.
Some of the most violent collisions in the universe can be nearly invisible to telescopes while still ringing through spacetime.
5. 🌌 Odd radio circles appear only to radio telescopes
In data collected in 2019, astronomers using Australia's ASKAP radio telescope noticed something unexpected: faint, giant circles that didn't match any known kind of object.
They named them odd radio circles, or ORCs. Some span roughly a million light-years, and they're barely visible, if at all, in ordinary optical images.
Sharper observations with the MeerKAT telescope showed that at least some ORCs surround distant galaxies. One explanation is an enormous expanding shock wave from an energetic event in the galaxy's core. Others involve old black-hole outbursts, powerful galactic winds or galaxies interacting.
Their origin is still unresolved.
The universe contains circles many times wider than the Milky Way that visible-light astronomy largely missed.
6. 🌌 The Stingray Nebula faded within twenty years
Most nebulae change over thousands or millions of years, far too slowly for us to notice.
The Stingray Nebula is different. Hubble photographed it in 1996 and again in 2016, and the comparison was startling. The nebula had faded dramatically, with its oxygen emission dropping by nearly a factor of 1,000, and its shape had visibly changed.
The likely cause is its central star. As the star's temperature changed, it produced less of the ultraviolet light that makes the surrounding gas glow, so the nebula dimmed.
The star may have gone through a brief burst of helium burning in a shell around its core, though its exact evolution is still being studied.
We usually see the universe in snapshots separated by millions of years. Here, a whole nebula transformed within two decades.
7. ☄️ 3I/ATLAS may carry chemistry from before the Sun
In July 2025, astronomers discovered 3I/ATLAS, only the third confirmed object known to have passed through our Solar System from interstellar space.
As it approached the Sun and warmed, telescopes found an unusually large share of carbon dioxide in the gas around it, and Webb detected methane.
Then came a remarkable result. A study published in Nature in June 2026 measured the comet's isotopes with Webb and ALMA. Its water contains more than ten times as much deuterium, a heavy form of hydrogen, as known comets, and its carbon isotopes differ from typical Solar System material.
Those measurements suggest it formed somewhere extremely cold, below about 30 kelvin. Compared against models of how the galaxy's chemistry has changed, its carbon points to formation roughly 10–12 billion years ago. That age is model-dependent rather than directly measured.
A comet from another star may preserve a record of planet formation from billions of years before the Sun existed.
8. 🌙 Charon's red pole is painted by Pluto
We've visited Charon's enormous canyons before. When New Horizons flew past in 2015, it found something else unexpected: a dark reddish cap around the moon's north pole, informally called Mordor Macula.
The leading explanation is that Pluto is painting it. Methane escapes from Pluto's atmosphere, and some of it drifts to Charon, where it freezes onto the extremely cold pole during the long polar winter.
Ultraviolet light then turns the frozen methane into more complex compounds. Over time, these build up into reddish organic material called tholins, which stay behind even after the methane leaves again.
The two worlds never touch. Yet one shapes the surface chemistry of the other.
One distant world may be slowly coloring another with molecules escaping from its own sky.
9. 🔴 Mars grows "spiders" every spring
Near Mars's south pole, orbiting spacecraft have photographed dark, branching patterns that look like enormous spiders. They're geological features called araneiform terrain.
In winter, carbon dioxide freezes into translucent slabs of ice over the ground. When spring sunlight returns, it passes through the ice and warms the surface beneath.
Ice at the bottom of the slab turns directly into gas, and pressure builds until the gas bursts out through cracks, carrying dust with it. The escaping gas carves branching channels under the ice, while the dust falls back as dark fans on top.
Mars Reconnaissance Orbiter has photographed these formations in detail as they return season after season.
Every Martian spring, sunlight turns frozen carbon dioxide into eruptions that etch spider-shaped patterns into the landscape.
10. ☄️ 16 Psyche is unusually rich in metal
Most asteroids are mixtures of rock and other primitive material. 16 Psyche stands out: radar, density estimates and its spectrum suggest that metal makes up roughly 30–60% of its volume.
One idea is that Psyche is part of the metal core of an early planetary building block, stripped of its rocky outer layers by violent collisions. If so, it would let us examine the kind of material that lies deep inside planets.
That origin isn't established. Psyche might instead have formed as an unusual mix of rock and metal from the start.
NASA launched the Psyche spacecraft in October 2023 to find out, and it's on its way to study the asteroid's composition, structure and history up close.
Earth's own core lies thousands of kilometers beneath us. Psyche may let us study something like a planet's interior without drilling through a planet.
11. 🌌 NGC 4258's water masers weighed a black hole
Under the right conditions, water molecules in space can amplify microwave radiation into intense, narrow beams, a natural maser. It's like a laser, but for microwaves.
In the galaxy NGC 4258, astronomers found water masers in a thin, warped disk orbiting close to the central black hole, seen nearly edge-on from Earth.
By measuring the masers' positions and speeds with radio telescopes spread across great distances, they reconstructed how the disk rotates. That gave exceptionally strong evidence for a compact central mass of roughly 39 million Suns.
The same measurements also gave a precise geometric distance to the galaxy, which helps calibrate the ladder of methods astronomers use to measure the universe.
Nature supplied the instruments: ordinary water molecules became radio beacons tracing gas around a black hole millions of light-years away.
12. 🌌 Galaxy clusters cast shadows on the oldest light
The cosmic microwave background has been travelling through space since the universe became transparent. Some of its light passes through galaxy clusters on the way to us.
Those clusters are filled with extremely hot gas, full of fast-moving electrons. When microwave background photons scatter off them, they gain a little energy. This is the thermal Sunyaev–Zeldovich effect.
The result is a distinctive distortion. At lower microwave frequencies, a cluster appears as a slight dimming in the background; at higher frequencies, as a slight brightening. ESA's Planck mission used this signature to find clusters across the whole sky.
The elegant part is that the cluster's gas doesn't need to shine brightly itself. Astronomers look at how it changes light arriving from behind.
The oldest light in the universe becomes a giant backlight, revealing hot gas in clusters billions of light-years away.
13. 🌌 Lensed quasars reveal small clumps of dark matter
Dark matter doesn't emit or reflect light. So how could we find small clumps of it that hold few or no stars?
Gravitational lensing helps. When a distant quasar sits almost directly behind a massive galaxy, the galaxy's gravity can split the quasar into several images, sometimes four arranged around it.
The positions and brightnesses of those images depend on all the mass along the light's path. A small, invisible clump of dark matter near one of the paths adds a tiny extra distortion.
In 2020, researchers analyzing Hubble observations of several lensed quasars reported evidence for such small clumps, supporting the prediction that cold dark matter should form structures smaller than visible galaxies.
What dark matter is made of remains unknown. But tiny imperfections in images from billions of light-years away can reveal where it gathers.
🌙 One last thought before you sleep
Think about 3I/ATLAS.
It may have formed around a star that shone long before the Sun, when the Milky Way was still young. At some point, perhaps through a close encounter with a planet, it was flung out of its home system.
Then it travelled. While it drifted between the stars, generations of stars were born and died. The Sun formed. Earth assembled, grew oceans and filled with life. People built telescopes.
And in 2025, this old traveller happened to pass through our neighborhood. Sunlight warmed it for the first time in billions of years, its ice turned to gas, and we caught that gas in our instruments and read a little of where it came from.
We can't visit most of the places we study. But every so often, the universe brings a piece of its history close enough for us to notice.
That's all for tonight. Thanks for wondering along with me. Good night, and clear skies. 🌌
— Kasi