Welcome back, and thanks for spending another evening here. Tonight we have twelve stops, including a few familiar ideas with new evidence to follow.
We'll retrace a star's journey from the heart of the Milky Way, meet a neutron star that takes most of a night to turn once, watch an asteroid shed six tails, and visit small planets that were already ancient when the Sun formed. At the end, there's a world whose atmosphere and surface frost keep exchanging places.
Get comfortable. 🌙
1. ⭐ S5-HVS1's motion points back to the Galactic center
We've met hypervelocity stars before. S5-HVS1 gives us something more specific: a route back to where one of them was launched.
The star moves at roughly 1,700 kilometers per second relative to the Milky Way, fast enough to escape. Combining its distance, motion across the sky and velocity along our line of sight lets astronomers run its trajectory backward.
The discovery study traced that path to the Galactic center about five million years ago. It provides unusually direct evidence for an encounter with Sagittarius A*, rather than merely a star moving fast somewhere in the galaxy.
The likely explanation is that the central black hole separated a binary system, capturing one star and ejecting the other. We haven't identified the lost companion, but the escaping star still carries a clue: its motion preserves the address of an encounter millions of years old.
2. 🧲 1E 161348−5055 takes more than six hours to turn once
Neutron stars usually rotate in seconds or fractions of a second. The object at the center of supernova remnant RCW 103 works on a very different clock.
1E 161348−5055 has an X-ray period of about 6.67 hours. Magnetar-like bursting activity supports the interpretation that this is its rotation period, making it an exceptionally slow magnetar.
The remnant is only a few thousand years old. That leaves a difficult question: how did a young neutron star lose so much angular momentum so quickly?
One proposed explanation involves a fallback disk, material left over from the supernova that could interact with the star's magnetic field and brake its rotation. Models of this process explore how that might work; the exact history remains uncertain.
A stellar remnant can pack more than the Sun's mass into a city-sized sphere, yet take longer than a quiet evening to complete a single turn.
3. 🌌 GN-z11 has evidence of a feeding black hole
We visited GN-z11 earlier for its place in the young universe. Webb spectroscopy has given us a more detailed question to ask about what was happening inside it.
We see the galaxy as it was roughly 430 million years after the Big Bang. Its spectrum contains highly ionized gas and signatures of unusually dense gas, consistent with material near an actively accreting black hole.
The researchers' analysis inferred a black hole of around a million solar masses, feeding rapidly. Its mass and growth rate depend on the interpretation of the spectrum, but the evidence adds a particular engine to the galaxy's story.
The challenge is explaining how it grew so early. A massive starting seed, unusually fast feeding, or some combination could help.
A distant galaxy's light can tell us more than when it existed. Hidden in its spectral lines may be evidence of a black hole already eating while the universe was still very young.
4. 🕳️ ASASSN-14li had a rhythm in its X-rays
When a star wandered too close to a supermassive black hole, the resulting tidal disruption event, ASASSN-14li, gave astronomers a temporary view of the material surrounding it.
Among its X-rays, researchers found a repeating brightness variation with a period of roughly 131 seconds. The signal persisted across observations for more than a year. The study used it to investigate the black hole's spin.
The interpretation depends on what produces the rhythm. If it traces motion close to the innermost stable orbit, its frequency constrains the black hole's rotation because spin changes where that orbit lies.
We aren't watching a resolved piece of debris circle the horizon. We're measuring changes in light and testing which motions could produce them.
Even so, a star's destruction supplied something surprisingly orderly: a short, persistent beat from material close to a black hole.
5. ⭐ HD 49798's companion is slowly spinning faster
The hot subdwarf HD 49798 has a compact companion, RX J0648.0−4418, whose X-ray pulses arrive every 13.2 seconds.
Its identity has been debated: a massive white dwarf or a neutron star? A timing study spanning about thirty years favors a massive white dwarf accreting material from the subdwarf's wind.
The measurements also show that the pulse period is gradually shortening. The companion is spinning up.
We've encountered rapidly rotating white dwarfs before, but here decades of pulses let astronomers follow a tiny change in the rotation and refine the binary's masses and orbit.
The system looks like a point from Earth. With enough patience, its X-rays reveal a stellar remnant turning a little faster as the years pass.
6. 🌠 The Taurid stream has a gravitationally gathered swarm
The Taurid meteor complex includes material associated with Comet Encke. Its bright fireballs have also prompted questions about whether much larger fragments might share the stream.
Planetary gravity can concentrate debris into a resonant swarm, rather than leaving it evenly spread along an orbit. Meteor observations support such a concentration for smaller objects.
That doesn't establish a vast hidden population of dangerous asteroids. A dedicated telescopic search, published in 2025, found no large swarm members and placed limits on how many roughly hundred-meter objects could be there.
Claims connecting the Taurids to particular prehistoric catastrophes remain speculative.
The useful picture is a meteor stream with structure that gravity keeps shaping. When Earth crosses a comet's debris, the material needn't be distributed evenly along the trail.
7. 🌌 NGC 4889 holds an enormous black hole without a brilliant quasar
At the center of the giant elliptical galaxy NGC 4889, in the Coma Cluster, lies a black hole whose mass has been estimated at around twenty billion Suns.
Astronomers inferred it from the motions of nearby stars. The exact mass has substantial uncertainty, but even the lower estimates describe an enormous object. ESA/Hubble's account explains the measurements and its comparatively quiet state.
You might expect something that massive to dominate the sky around it. Yet NGC 4889's center isn't currently shining as a brilliant quasar.
A black hole's mass and its brightness tell us different things. Mass records what it has accumulated; the light from its surroundings depends on the supply and behavior of material falling inward now.
An immense black hole can therefore be easy to miss in light while remaining unmistakable in the motions of stars.
8. 🪐 Kepler-444's five small planets formed long before the Sun
Kepler-444 is roughly eleven billion years old, more than twice the age of our Solar System. Five planets smaller than Earth orbit its main star, all with years shorter than ten days.
We've met an ancient giant planet before. This system tells us something about the early formation of small, likely rocky worlds.
The discovery study used the star's oscillations to estimate its age. The result showed that terrestrial-sized planets could form when the universe had far fewer heavy elements than it does today.
These planets orbit too close to their star to be Earth analogues. Their significance is the time they have had.
When the Sun began forming 4.6 billion years ago, these little worlds had already spent billions of years going around their star.
9. ☄️ 311P/PANSTARRS grew six tails
In 2013, Hubble observed an object in the asteroid belt with six comet-like tails. It was then called P/2013 P5 and is now known as 311P/PANSTARRS.
The tails record separate releases of dust, which sunlight pushed into different-looking trails. Hubble's observations showed their appearance changing dramatically within thirteen days.
The favored explanation involves rapid rotation shedding loose surface material, rather than the evaporation of ice that powers a typical comet. Uneven thermal radiation can gradually change an asteroid's spin, a process called the YORP effect.
The details of the dust release remain under study. But the object shows why appearance alone can mislead us.
A tail can mean that ice is escaping as gas. Or it can mean an asteroid is losing its grip on its own surface.
10. 🕳️ ASASSN-14ko may be a star losing material on repeated visits
A tidal disruption doesn't always have to destroy a star in one encounter. On a sufficiently close orbit, a star might lose some of its outer layers, survive, and return.
ASASSN-14ko is a candidate for this kind of repeating partial tidal disruption.
Researchers identified a series of flares about 114 days apart in the galaxy ESO 253-3. The pattern was consistent enough that they predicted later flares and watched them arrive. NASA's account describes the observations and the competing explanations.
In the partial-disruption picture, each close passage removes more material. That debris then powers another flare as it falls toward the black hole.
The model is still an interpretation, rather than a direct view of the star. But it offers an unsettling possibility: a stellar catastrophe that leaves enough of the star to happen again.
11. 🌙 Deimos may collect pieces blasted off Mars
Impacts on Mars can launch material fast enough to escape the surface. A small fraction of that ejecta can eventually reach its moons, Phobos and Deimos.
That means Deimos's surface may contain pieces of Mars mixed with the moon's own material. It doesn't settle the moon's uncertain origin, but it adds another history to the grains resting there.
Transport models suggest Martian ejecta could preserve material from different geological eras and regions. Sampling a moon could therefore help us study the planet beneath it.
JAXA's MMX mission targets Phobos for sample return and will also observe Deimos. A returned Martian grain would need careful identification; we can't assume every sample would contain one.
Still, a small moon can be more than a destination of its own. It may also be a collection tray for fragments of another world.
12. 🪐 Pluto's atmosphere trades material with its surface frost
Pluto's thin atmosphere is made mostly of nitrogen. That nitrogen also exists as ice on the ground, and sunlight helps move it between the two.
Over Pluto's 248-year orbit, seasons, changing solar distance and the slow response of surface ice affect atmospheric pressure. For decades, pressure rose even while Pluto moved farther from the Sun: stored heat complicated the simple expectation of immediate cooling.
Astronomers track the atmosphere through stellar occultations, measuring how a background star's light changes as it passes behind Pluto's air.
A 2026 analysis of occultations from 2017–2023 found evidence of a pressure plateau followed by a possible decline. Haze affects the interpretation, and further measurements are needed to confirm the change.
The long-term evolution remains uncertain, but the exchange itself is real. On Pluto, some of the material making up the sky can settle back onto the ground as frost.
🌙 One last thought before you sleep
Think about the small planets around Kepler-444.
We tend to use Earth as our starting point for imagining a world's history. Four and a half billion years already feels like more time than the mind can comfortably hold.
Yet when Earth was assembling, those planets were old. They had orbited their star through billions of years before there was a Sun to shine on our oceans, before there were oceans here at all.
Their short years have kept passing while our own world changed from molten rock into somewhere that can look back at them.
Astronomy gives us many ways to feel small. Tonight, perhaps the gentler one is time: our world's beginning was an ordinary moment in the long lives of other worlds.
That's all for tonight. Thanks for wondering along with me. Good night, and clear skies. 🌌
— Kasi