Welcome back, and thanks for spending another evening here. Tonight we have fourteen stops, and many of them are about things that aren't quite what they seemed: homes that may not exist, steady lights that flicker, and planets that were never there.
We'll watch a small star nibbling a brown dwarf one bite at a time, read the rubble of Neptune's lost moons, find out that our home supercluster may be only a suburb, ask whether Venus once ate its own moon, and hunt for a planet that astronomers saw for decades but that never existed. At the end, we'll ask whether the universe goes on forever.
Get comfortable. 🌙
1. ⭐ ZTF J0440+2325 is a star slowly snacking on a brown dwarf
When a star and a close companion get too cozy, the usual ending is quick and brutal: the star swallows it. That's the fate expected for Earth when the Sun swells into a red giant.
Years ago, Kevin Burdge of MIT spotted a strange signal in data from the Zwicky Transient Facility, a sky survey at Palomar Observatory. The light rose and fell in a shape like a triangle. "I remember first looking at this and thinking, stars don't make triangular waveforms like this," he said. The puzzle sat for years.
When Burdge and graduate student Aaron Householder finally followed it up, they found a small star about 300 light-years away, about 85 times Jupiter's mass, with a brown dwarf of about 25 Jupiter masses circling it every 87 minutes. Their whole orbit would fit inside the Sun.
The star is pulling gas off the brown dwarf, about a hundred-thousandth of Earth's mass every year. The stream slams straight into the star's surface and makes a hot spot, and the triangle is that fireball swinging in and out of view.
It's the first time anyone has seen this, published in October 2026. At this pace, the meal could last billions of years.
Not every star gulps its companions. Some prefer to take very small bites.
2. 🌙 Neptune's little moons are made of shattered worlds
Neptune's moons are a mess. Unlike the other giant planets, it has no orderly family of large moons. Its giant moon Triton probably began life elsewhere, as a visitor from the Kuiper Belt that Neptune captured. What happened to the rest?
New evidence came from Neptune's tiny inner moons, five of which Voyager 2 found in 1989 just outside the planet's rings. In 2026, a Caltech team led by Ryleigh Davis used Webb to take the first spectra of three of them, Larissa, Galatea and Proteus, along with the rings.
They found clay minerals on Larissa, Galatea and in the rings, and no water ice at all. That's bizarre this far from the Sun, where almost everything is icy. And clays need liquid water to form, deep inside a body big enough to melt its ice.
The team's explanation: Neptune once had big icy moons, and Triton's arrival wrecked them. The small moons we see today gathered from the debris, their insides turned out. Another possibility is that a Pluto-sized object passed too close and was torn apart. Each moon also shows a hydrated mineral nobody can identify.
Neptune's smallest moons may be the scattered insides of worlds that no longer exist.
3. 🕳️ GW250114 caught black holes obeying Hawking's rule
In 1971, Stephen Hawking put forward something simple and strange: the total surface area of black holes can never shrink. When two merge, they lose energy in gravitational waves, and the new black hole may spin faster, which shrinks its area. Even so, the theorem says, the final area must be larger than the two before it.
For decades, nobody could check. A first test in 2021, using LIGO's very first detection, was suggestive but only about 95% confident. Then, on January 14, 2025, LIGO caught GW250114, two black holes of about 30 to 40 Suns colliding 1.3 billion light-years away. After ten years of upgrades, the signal was far clearer than the first detection in 2015.
After merging, the new black hole "rang" like a struck bell, and for the first time the team confidently picked out two distinct tones. From those, they worked out its mass, its spin and so its area.
The two original black holes had a combined surface area of about 240,000 square kilometers, roughly the size of Oregon. The final one had about 400,000, roughly the size of California. This time the confidence was 99.999%.
Right after the 2015 detection, Hawking phoned Kip Thorne to ask whether LIGO could test his theorem. He died in 2018. "If Hawking were alive, he would have reveled in seeing the area of the merged black holes increase," Thorne said.
Even when black holes collide, the rules hold.
4. 🌌 Laniakea, our home supercluster, may not exist
Your cosmic address goes something like this: Earth, the Solar System, the Milky Way, the Local Group, and then a vast supercluster. In 2014, a team led by Brent Tully of the University of Hawaii drew that supercluster's borders for the first time.
They did it by watching how galaxies move. Subtract the expansion of the universe, and the leftover motion shows where gravity is pulling. The team found boundaries where those flows split apart, like the ridges that divide rivers into separate watersheds. Inside the boundary, everything drains inward.
They called it Laniakea, Hawaiian for "immense heaven," in honor of the Polynesian navigators who crossed the Pacific by the stars. It's about 500 million light-years across, with 100,000 galaxies.
Ten years later, a team led by Aurelien Valade at the Leibniz Institute for Astrophysics Potsdam remapped the flows using 56,000 galaxies, this time tracking how likely each structure is to be real. Their verdict: Laniakea is probably merely an appendage of the much larger Shapley basin, and "may not even exist as a separate entity."
We may live not in a great capital, but in the suburbs of something much bigger.
5. ⭐ FU Orionis flared up in 1936 and never calmed down
In 1936, a young star in Orion did something baffling. Over a few months, FU Orionis became a hundred times brighter. But unlike an exploding star, FU Orionis has dimmed only languidly ever since, and it's still in outburst nearly 90 years later.
It's a star still growing, fed by a disk of gas and dust. In most young stars, the star's magnetic field holds the disk at arm's length. But FU Orionis's disk became unstable and began dumping gas fast enough to push right up against the star's surface. Today the disk outshines the star it's feeding.
Astronomers now know of a whole class of these eruptive young stars, named after FU Orionis. In 2024, a team led by Adolfo Carvalho of Caltech used Hubble to look at FU Orionis in ultraviolet light, closer to the star's surface than anyone had before. Where the speeding disk gas crashes into the star, they found a temperature of about 16,000 kelvins, nearly three times as hot as the Sun's surface and almost twice what models predicted.
"The fact we saw so much extra — it was much brighter in the ultraviolet than we predicted — that was the big surprise," said co-author Lynne Hillenbrand.
For almost a century, a baby star has been in the middle of a growth spurt that refuses to end.
6. 🪐 Kepler-413b has seasons that change on a whim
Earth's seasons are reliable because our planet's tilt is steady. It slowly wobbles like a spinning top, but one full wobble takes about 26,000 years.
Kepler-413b isn't so patient. This planet, about 65 times Earth's mass, circles a close pair of orange and red dwarf stars every 66 days, 2,300 light-years away in Cygnus. Its spin axis wobbles so wildly that its tilt can change by as much as 30 degrees in just 11 years. NASA described its seasons as "so erratic you would hardly know whether to wear Bermuda shorts or a heavy overcoat."
Its orbit wobbles too, tilted about 2.5 degrees from the orbit of its two stars, so it sometimes passes in front of them as seen from Earth and sometimes misses. "Looking at the Kepler data over the course of 1,500 days, we saw three transits in the first 180 days — one transit every 66 days — then we had 800 days with no transits at all," said Veselin Kostov, who led the study. "After that, we saw five more transits in a row."
Nobody knows what knocked it out of line. Unseen planets might be tugging on it, or perhaps a third star nearby.
On Kepler-413b, you couldn't trust next year's calendar, never mind the weather.
7. 🌌 PicII-503 carries the ashes of the first stars
The first stars formed from nothing but hydrogen and helium. Every heavier element, every atom of carbon or iron, had to be made inside stars and spread by their explosions. Astronomers hunt for the second generation, stars that formed from gas sprinkled only with the ashes of the first.
In 2026, a team led by Anirudh Chiti of Stanford found one in Pictor II, a tiny, ancient galaxy orbiting the Milky Way with only several thousand stars. They spotted it using a special filter on the Dark Energy Camera in Chile that estimates a star's metals from a picture alone, and then followed up with the Magellan and Very Large Telescopes.
PicII-503 has less than 1/40,000th of the Sun's iron, the lowest ever measured in a star outside the Milky Way. But it has more than 1,500 times the Sun's ratio of carbon to iron.
That pattern points to gentle, low-energy explosions in the first stars. Heavy iron near their cores fell back inside, while lighter carbon in their outer layers escaped. A more powerful blast would have flung everything clean out of such a small galaxy.
The Milky Way's outskirts hold many stars with the same carbon-rich signature. PicII-503 suggests they came from little galaxies like this one, swallowed long ago.
In one faint star, a tiny galaxy has kept a record of the universe's first fires.
8. ☄️ Chariklo's rings are changing in front of us
For a long time, rings belonged only to the giant planets. Then, in 2013, astronomers found two rings around Chariklo, a small body only about 250 kilometers across that orbits between Saturn and Uranus.
The rings are far too narrow to photograph, even for Webb. Instead, astronomers wait for Chariklo to pass in front of a distant star. As each ring crosses, the starlight dips for a moment, revealing how much it blocks.
Four years ago tonight, on October 18, 2022, Webb watched one of these crossings, the first ever predicted for and caught by the telescope. Pulling it off meant knowing Chariklo's orbit, the star's position and Webb's own path around its station 1.5 million kilometers from Earth with extraordinary precision.
When a team led by Pablo Santos-Sanz compared the result with a decade of earlier crossings, they found the two rings had changed in opposite ways. The inner ring now blocks more light than before, and the outer ring less. Rings around small worlds had been thought of as stable.
Some of the difference might come from the colors of light used in different observations, and the team can't yet say what's driving the change.
Even the rings of a tiny world far from the Sun can be restless.
9. 🧲 The Crab Nebula's steady glow suddenly flared
The Crab Nebula is the wreckage of a star whose explosion was seen from Earth in the year 1054. At its heart spins a pulsar, a neutron star turning 30 times a second. Apart from the pulsar's beat, astronomers believed the nebula was a virtually constant source of high-energy light, one of the steadiest beacons in the sky.
Then, starting in 2009, NASA's Fermi telescope and Italy's AGILE satellite caught it flaring in gamma rays, light tens of millions of times more energetic than visible light. On April 12, 2011, came a "superflare" about 30 times the nebula's normal gamma-ray output and five times more powerful than any before. Four days later, an even brighter flare erupted. Within a couple of days, it had all faded away.
NASA's Chandra X-ray Observatory was ready and looking during the flare, and it saw nothing obviously change.
Theorists think the flares come from sudden rearrangements of the intense magnetic field near the neutron star, flinging electrons to nearly the speed of light. They must happen within about a third of a light-year of the pulsar, but nobody has pinned down exactly where. "These superflares are the most intense outbursts we've seen to date, and they are all extremely puzzling events," said Alice Harding of NASA Goddard.
Even the steadiest light in the sky has a temper.
10. 🌑 Venus may have eaten its own moon
Earth has a big moon. Venus, almost Earth's twin in size, has none. Why?
The usual answers involve drama: maybe Venus never suffered the right kind of giant collision to make a moon, or maybe a later collision destroyed it. In 2026, Stephen Kane of UC Riverside and his colleagues found that no catastrophe may be needed.
The key is spin. Earth turns once a day, and through the tides, our planet's spin slowly pushes the Moon outward. Venus takes 243 Earth days to turn once. Around such a slow spinner, the tides work in reverse, dragging a moon inward.
Kane simulated moons from half to ten times the mass of ours. In most runs, the moon spiraled inward until it crashed into Venus, and bigger moons met that fate faster. The full study shows that the outcome depends on how fast young Venus spun, and a lunar-mass moon sits right at the edge of survival. But for many plausible starts, the moon is lost through tides alone.
"When I made this discovery, I was shocked," Kane said. Proof would be hard to find, because Venus resurfaced most of itself around a billion years ago. Any scar may lie deep inside.
Venus may not be moonless by accident, but by the slow logic of its own sluggish spin.
11. 🌌 Crater II is a giant galaxy that moves too slowly
In 2016, astronomers found a new galaxy orbiting the Milky Way in the constellation Crater. Crater II turned out to be one of the largest of the Milky Way's companions, with half its light spread within about 3,600 light-years of its center. Only the two Magellanic Clouds and the Sagittarius dwarf are bigger. Yet it's so faint it's barely there, one of the most diffuse galaxies known. They called it "the feeble giant."
Then a team led by Nelson Caldwell measured how fast 62 of its stars are moving. The answer was about 2.7 kilometers per second, the coldest of any dwarf galaxy measured. Earth moves around the Sun more than ten times faster.
Before the measurement came out, Stacy McGaugh had used an alternative theory of gravity called MOND, which does away with dark matter, to predict a very low value of about 2.1. Caldwell's team found that dark matter can still explain the stars' motions, but it makes Crater II the most extreme low-density outlier among the Milky Way's dwarf galaxies.
One idea is that the Milky Way's tides have stripped it. But a 2022 study found that tides alone can't explain how a galaxy can be this big and this cold in the standard picture.
A faint giant on our doorstep is quietly testing what gravity really is.
12. 🔭 Vulcan was a planet astronomers saw, but that never existed
In the 1840s, Urbain Le Verrier found Neptune "at the tip of his pen," by working out what was tugging on Uranus. So when he found that Mercury's orbit also drifted in a way no known planet could explain, the answer seemed obvious: another hidden planet, closer to the Sun.
On March 26, 1859, a country doctor named Edmond Lescarbault, between patients, climbed into his little observatory in a stone barn and watched a round dot creep across the face of the Sun. When he wrote to Le Verrier months later, the great astronomer took a train and then a 12-mile walk to question him, and came away convinced. The planet became known as Vulcan.
For about 20 years, people kept seeing it. During the great eclipse of 1878, the astronomer James Watson spotted a bright point near the Sun that wasn't on his star chart and declared it Vulcan. Newspapers around the world announced the find within days.
But Vulcan was never there. In 1915, Albert Einstein used his new theory of gravity, general relativity, to calculate Mercury's orbit, and it matched perfectly with no extra planet. The drift came from the Sun bending space and time. Einstein said he felt palpitations of the heart and was too excited to work for three days.
Sometimes the missing planet is really a missing idea.
13. 🌡️ A water shadow took the young universe's temperature
The afterglow of the Big Bang, the cosmic microwave background, fills all of space at about 2.7 degrees above absolute zero. As the universe expands, it should cool, so in the past it must have been warmer. But measuring the temperature of the universe billions of years ago is hard.
Dominik Riechers of the University of Cologne and his colleagues found a clever way. Using the NOEMA observatory, they studied HFLS3, a galaxy furiously making stars, seen as it was just 880 million years after the Big Bang. It sits inside a cloud of cold water vapor, and that water absorbs a little of the microwave background shining from behind it, casting a faint shadow.
How dark the shadow is depends on the background's temperature. The answer was between about 16 and 30 kelvins, about seven times warmer than today, right in line with what the standard picture of an expanding universe predicts.
There's a lovely twist. The trick only works in the young universe. By about 1.5 billion years after the Big Bang, the background had grown too cold for any water cloud to cast such a shadow.
Through a shadow of water, we read a thermometer left out 12.8 billion years ago.
14. 🌌 The universe may or may not go on forever
Is the universe infinite? It sounds like a question for philosophers, but astronomers can actually test part of it.
On a curved surface like Earth's, triangles have angles adding up to more than 180 degrees, and lines that start parallel can meet. Space itself could be curved the same way, and if it curved back on itself, the universe could be finite with no edge, like the surface of a ball. Astronomers check by measuring the size of the hot and cold patches in the cosmic microwave background. Curved space would distort them. Instead, they look just the size they should in flat space.
But flat doesn't have to mean infinite. Your neighborhood looks flat even though Earth is round. Or space could be flat and still wrap around, like a video game where leaving one edge brings you back on the other side. If so, we might see the same patterns twice, as matching circles in the microwave background. Searches of the WMAP and Planck data have found none, so any loop around the universe passing through us must be longer than 98.5% of the distance across what we can see. Some shapes, though, could still hide shorter loops that miss us entirely.
And only a limited amount of information about the universe can ever reach us, however long we wait. What lies beyond our horizon, we can only infer.
We may live in an infinite universe, or a finite one that only looks endless. We may never know which.
🌙 One last thought before you sleep
So many of tonight's stories were about the gap between what we see and what is.
A steady nebula flickered. A planet was seen again and again, and never existed. A home supercluster dissolved into a bigger one. A ring system that should have been settled turned out to be restless, and a galaxy that should have been bustling with motion barely stirs.
And yet, again and again, the truth was findable. A triangle in a light curve became a star's slow meal. A shadow of water became a thermometer. A ringing black hole proved a theorem written half a century ago.
We see only a small patch of a universe that may go on without end. But what we can see, we can learn to read.
The universe keeps correcting us, and that is how we come to know it.
That's all for tonight. Thanks for wondering along with me. Good night, and clear skies. 🌌
— Kasi