Pull up a blanket; we're heading out again. Tonight's thirty stops are all new ones.
We'll meet two dead stars whirling around each other every seven minutes, visit a planet whose atmosphere is being blown into a gigantic comet-like tail, look for the probable ocean hidden inside Pluto, ride along with a spacecraft that flew through the Sun's outer atmosphere, encounter galaxies that stopped making stars astonishingly early, and finish with something surrounding you right now: particles that have been traveling since about one second after the Big Bang.
Let's go. 🌙
1. ⭐ ZTF J1539+5027 — two dead stars orbit each other every seven minutes
Imagine two stars completing an entire orbit in less time than it takes to make a cup of tea.
ZTF J1539+5027 is a binary of two white dwarfs separated by only about one-fifth of the distance between Earth and the Moon. They orbit each other roughly every 6.9 minutes.
Astronomers found the system because, from our point of view, the two stars repeatedly eclipse each other. Every orbit also carries away energy as gravitational waves, so the stars are slowly spiraling closer together. Eventually they may transfer mass or merge, depending on the details of their evolution.
The system is especially valuable because future space-based gravitational-wave observatories such as LISA should detect binaries like this one very clearly.
These are two stellar corpses completing thousands of orbits a month while gradually radiating their orbital energy into spacetime itself.
2. 🪐 GJ 436 b has an enormous comet-like hydrogen tail
GJ 436 b is a Neptune-sized planet orbiting extremely close to a red dwarf about 32 light-years away.
Ultraviolet observations revealed something spectacular: the planet is wrapped in an enormous cloud of hydrogen extending millions of kilometers into space.
Its star's radiation heats the upper atmosphere until hydrogen escapes. Radiation pressure and the surrounding stellar environment then sculpt the escaping gas into something resembling a giant cometary tail.
The planet isn't about to disappear. Its reservoir is large and the loss rate isn't high enough to destroy it quickly. But we're directly watching atmospheric escape on another world.
Planetary atmospheres aren't permanent shells. Given enough radiation, a star can slowly blow a planet's sky into space.
3. 🌌 The Milky Way is warped
Textbook illustrations usually show our galaxy as a perfectly flat spiral disk. It isn't.
Measurements of stars across the Milky Way show that its outer disk bends and twists, a bit like a slightly warped vinyl record.
Mapping this is hard because we live inside the disk, but surveys using Cepheid stars, hydrogen gas and, above all, precise stellar positions and motions have reconstructed the distortion.
The warp probably reflects gravitational interactions with the Milky Way's dark-matter halo, satellite galaxies such as the Large Magellanic Cloud, or the continuing infall of material.
So our galaxy isn't a rigid structure. It flexes, oscillates and responds to the gravity around it. If we could somehow view the Milky Way from far outside, its elegant spiral would show a distinctly crooked edge.
4. 🕳️ A black hole's photon sphere can force light into near-orbits
Close to a nonrotating black hole, at about 1.5 Schwarzschild radii from the center, lies a remarkable region where, mathematically, photons can travel in circles. It's called the photon sphere.
Such an orbit is unstable. The tiniest disturbance sends the photon either outward or down toward the event horizon.
Even so, it has spectacular observational consequences. Light passing near this critical region can loop partway, or even several times, around a black hole before escaping. That's what produces the sequence of ever-narrower photon rings predicted around black-hole shadows.
An observer near a black hole could, in principle, receive photons that had already traveled around it before arriving.
Gravity becomes so intense that light can chase its own path around darkness.
5. 🧊 Pluto probably has an ocean beneath its ice
New Horizons transformed Pluto from a frozen dot into a geologically complicated world, and one of the most intriguing possibilities it raised is a present-day subsurface ocean.
The strongest clues come from Pluto's geology and the enormous Sputnik Planitia basin. The basin sits close to the point directly opposite Pluto's moon Charon, a location that's easy to explain if the basin holds extra mass, possibly including liquid water pushed up beneath a relatively thin ice shell.
Models of Pluto's thermal evolution also show that an internal ocean could survive if the icy shell insulates it well enough.
The ocean hasn't been detected directly, so it remains an inference rather than an established observation. But the possibility is remarkable.
More than five billion kilometers from the Sun, beneath nitrogen glaciers and mountains of water ice, Pluto may still be hiding liquid water.
6. 💥 ASASSN-15lh — an explosion so luminous its identity became a mystery
In 2015 astronomers detected ASASSN-15lh, an extraordinarily luminous transient.
It was first classified as an extreme superluminous supernova, radiating at its peak hundreds of billions of times the luminosity of the Sun. That interpretation soon became controversial.
Its position close to the nucleus of its host galaxy, along with its unusual ultraviolet behavior, led researchers to suggest that it might instead have been a tidal disruption event: perhaps a star torn apart by a rapidly spinning supermassive black hole. Its true nature is still debated.
It's one of astronomy's useful reminders that classification follows evidence, not spectacle. We unquestionably saw an astonishing release of energy.
Exactly what died to produce it is the harder question.
7. 🪐 Kepler-11 packs six planets into an astonishingly tiny region
The Kepler-11 system has six known transiting planets. Five of them orbit their star closer than Mercury orbits the Sun, and the sixth isn't much farther out.
Before the Kepler mission, astronomers didn't know whether such tightly packed multiplanet systems were common, or even whether stable arrangements like this formed naturally.
Because the worlds tug on one another gravitationally, transit timing variations let researchers estimate their masses. Several turned out to have surprisingly low densities, implying thick envelopes of light gases.
Kepler-11 showed that nature can build planetary systems utterly unlike ours: six worlds crowded into a region where the Solar System fits essentially one planet.
8. 🧲 A neutron star's crust may be billions of times stronger than steel
A neutron star's crust is made of atomic nuclei embedded in an extraordinarily dense sea of electrons, giving way to increasingly exotic, neutron-rich matter at depth.
Simulations suggest this material could be around ten billion times stronger than steel in terms of the strain it takes to break it.
That matters because neutron stars can support tiny deformations, "mountains," despite their tremendous gravity. Calling them mountains is generous: one might be only centimeters high.
Yet because the star is so dense, even such minuscule bumps can involve enormous masses, and a spinning, lopsided neutron star could give off continuous gravitational waves.
On Earth, mountains rise kilometers. On a neutron star, gravity is so overpowering that a bump centimeters high can become astrophysically significant.
9. 🌞 Parker Solar Probe became the first spacecraft to fly through the Sun's corona
In 2021 scientists announced that NASA's Parker Solar Probe had crossed the Alfvén critical surface and entered the solar corona. We had, in effect, sent a spacecraft into the Sun's outer atmosphere.
Parker survives because the corona, despite temperatures of millions of degrees, is incredibly thin. Temperature describes how energetic the particles are; it doesn't mean enough of them hit the spacecraft to transfer heat the way dense material on Earth would. A sophisticated heat shield protects the probe from the intense sunlight.
Parker has since plunged through this environment again and again, studying magnetic fields, plasma and the origins of the solar wind.
For most of history, all we could do was look at the Sun. Now we've built something that can fly through part of it.
10. 🌌 The Tadpole Galaxy carries a stellar tail hundreds of thousands of light-years long
UGC 10214, nicknamed the Tadpole Galaxy, trails an extraordinary tail of stars stretching roughly 280,000 light-years.
The likely culprit was a gravitational encounter with another galaxy. During close interactions, gravity can pull stars and gas out into immense tidal tails without individual stars ever needing to collide.
Hubble images reveal clusters of young stars forming within the Tadpole's tail. This is galactic violence acting as creation: a close encounter distorted an entire galaxy, dragged material across intergalactic distances and, at the same time, built places where new stars could form.
Galaxy collisions don't look like car crashes. They look like gravity slowly reaching across hundreds of thousands of light-years and rearranging billions of suns.
11. 🌋 Io's thin sulfur-dioxide atmosphere partly collapses in Jupiter's shadow
Io has a thin atmosphere dominated by sulfur dioxide, but it isn't stable the way Earth's is.
When Io passes into Jupiter's shadow, its surface temperature drops, and observations indicate that a substantial amount of the atmospheric sulfur dioxide can freeze onto the surface. When sunlight returns, the frost sublimates and replenishes the atmosphere, while volcanic eruptions supply extra gas.
So Io's atmosphere is caught in a bizarre cycle between geology and sunlight. Part of its sky can literally turn to frost and later return to gas.
On Earth, weather moves water between the surface and the atmosphere. On Io, the atmosphere itself partly freezes onto the ground every orbit.
12. 🔭 Einstein rings turn galaxies into luminous circles
When a distant galaxy, a massive foreground object and Earth line up almost perfectly, gravitational lensing can produce an Einstein ring.
Light from the background galaxy reaches us along several curved paths around the foreground mass. With near-perfect symmetry, those distorted images merge into a glowing circle.
The effect follows from general relativity and is now routinely observed. And Einstein rings aren't just beautiful: their geometry lets astronomers weigh the foreground lens, including matter that gives off no light, and magnifies galaxies that would otherwise be too faint to study.
One galaxy becomes a natural telescope for another. Every so often the universe lines things up so perfectly that gravity draws a circle out of light.
13. 🪐 HAT-P-7b has clouds that appear to move around the planet
Kepler watched HAT-P-7b, an intensely heated hot Jupiter, through many orbits, and astronomers noticed that the position of its brightest region shifted over time.
One interpretation involves atmospheric circulation and changing cloud patterns. On the cooler nightside, minerals such as corundum (aluminum oxide, the stuff that forms rubies and sapphires when impurities are present) could condense into clouds. Those clouds might then drift around the planet before evaporating on the scorching dayside.
We can't photograph individual clouds on HAT-P-7b. Instead, astronomers infer its global weather from tiny variations in the combined light of planet and star.
We've reached the point where we can study changing weather on worlds more than a thousand light-years away.
14. ⭐ R136a1 is among the most massive stars known
Inside the Tarantula Nebula in the Large Magellanic Cloud lies R136a1, one of the most massive stars known. Current estimates put it well over 100 solar masses, and it may have started life considerably heavier.
Stars like this live extravagantly and briefly. R136a1 is millions of times more luminous than the Sun and drives ferocious stellar winds, shedding enormous amounts of material.
Radiation pressure is a fundamental limit on how massive stars can get, because intense light pushes outward against the matter falling in. R136a1 sits near that extreme edge of stellar physics.
The Sun has been shining for 4.6 billion years and has billions left. A monster like R136a1 burns through its whole existence in only a few million years.
15. 🌑 The Moon has permanently shadowed regions colder than Pluto
Near the lunar poles are craters whose floors essentially never see direct sunlight. Some drop below roughly 40 kelvin, which makes them among the coldest places ever measured in the Solar System, colder than Pluto's typical surface.
These regions act as cold traps. Water molecules and other volatile substances that wander in can stay frozen for immense stretches of time. Spacecraft have confirmed water ice in the polar regions, which makes these sites especially interesting for future exploration.
The Moon holds extraordinary thermal extremes. Sunlit ground near the equator can get hotter than boiling water, while some polar shadows sit only a few dozen degrees above absolute zero.
Both exist on the same small world right beside Earth.
16. 🕳️ HLX-1 is one of the strongest intermediate-mass black-hole candidates
HLX-1, or Hyper-Luminous X-ray Source 1, lies in the galaxy ESO 243-49.
Its extraordinary X-ray luminosity is hard to explain with an ordinary stellar-mass black hole unless it breaks the usual assumptions about how accretion works. That makes it one of the strongest candidates for an intermediate-mass black hole, possibly weighing thousands to tens of thousands of solar masses.
Its brightness also varies dramatically, hinting at changes in how it's feeding.
Objects like HLX-1 matter because intermediate black holes may be the evolutionary stepping stones between stellar remnants and the monsters in galactic centers. Finding one is like discovering a missing evolutionary fossil, not of biology, but of gravity.
17. 🌊 Saturn's moon Dione may also hide an ocean
Enceladus may not be Saturn's only ocean moon.
Measurements of Dione's gravity and shape, combined with models of its interior, support the possibility of a subsurface ocean lying tens or perhaps hundreds of kilometers beneath its icy surface.
Unlike Enceladus, Dione isn't spraying obvious plumes into space today, which makes confirmation much harder. Its surface does show fractures and tectonic features that point to a complicated geological past.
If Dione really does have an ocean, the outer Solar System may hold many more liquid reservoirs than early astronomers imagined. Liquid water wouldn't be an Earthly rarity confined to planets at comfortable distances from their stars.
It could be common beneath the ice throughout the outer Solar System.
18. 🌌 The Milky Way is cannibalizing the Sagittarius Dwarf Galaxy
Our galaxy is tearing apart a smaller neighbor right now.
The Sagittarius Dwarf Spheroidal Galaxy has passed through the Milky Way's gravitational field again and again. Each passage strips away stars, leaving enormous stellar streams wrapped around our galaxy.
Astronomers map these streams using stellar positions, velocities and chemistry. They're powerful probes of the Milky Way's gravity, and therefore of its invisible dark-matter halo.
The process also shows how large galaxies grow. The Milky Way wasn't assembled peacefully from a single cloud; it has repeatedly swallowed smaller systems and absorbed their stars.
Some stars in our galactic halo are immigrants from galaxies the Milky Way destroyed.
19. 💥 Pair-instability supernovae may completely obliterate stars
Most massive stellar explosions leave something behind: a neutron star or a black hole.
But theory predicts that stars in certain extreme mass ranges can undergo a pair-instability supernova. At enormous core temperatures, energetic photons can turn into electron–positron pairs. That drains the radiation pressure holding up the core, which then contracts and triggers runaway nuclear burning.
Under the right conditions, the resulting explosion is so violent that the entire star is blown apart. No neutron star. No black hole. Nothing but expanding debris.
Astronomers have identified candidate events, but pinning down an unambiguous textbook example is still difficult.
If the mechanism works as predicted, nature has a way for a star not merely to die, but to erase its stellar body completely.
20. 🪐 TrES-2b reflects less light than coal
TrES-2b is one of the darkest exoplanets ever measured. Kepler observations indicate that it reflects less than about one percent of the visible light falling on it. Fresh asphalt and coal would look reflective by comparison.
Its atmosphere is too hot for bright ammonia clouds like Jupiter's, while gases including sodium and potassium soak up visible light efficiently.
Yet it wouldn't look perfectly black up close. It's hot enough to give off thermal radiation, and parts of it might glow a dim red.
So TrES-2b is a giant world whose atmosphere swallows almost all the visible starlight that reaches it. Against space, it would look like a vast dark silhouette faintly glowing with its own heat.
21. 🌀 The Whirlpool Galaxy is interacting with a smaller companion
The Whirlpool Galaxy, M51, has some of the most beautifully defined spiral arms known, and they're not just decoration.
Right next to it sits the smaller galaxy NGC 5195, and the gravitational interaction between the two has probably helped strengthen M51's spiral structure and trigger star formation. Computer simulations show how galactic encounters can set up density waves that compress gas and produce prominent arms.
The pair illustrates a recurring theme in astronomy: galaxies evolve partly through their relationships. Their shapes, star-formation rates and central black holes can all be influenced by their neighbors.
The Whirlpool's famous symmetry may owe much of its beauty to another galaxy gravitationally disturbing it.
22. ☄️ 2I/Borisov was an unmistakable comet from another star system
Two years after 'Oumuamua, astronomers found another object on an unbound, interstellar path. This time there was little doubt about what it was.
2I/Borisov showed a clear coma and tail: it was an interstellar comet. Spectroscopy picked up familiar cometary molecules, letting astronomers compare material formed around another star with comets born in our own Solar System.
Borisov turned out to be both alien and surprisingly recognizable. It probably formed in a distant planetary system, was flung out by gravity, drifted through interstellar space for an unknown length of time, and happened to pass through ours.
For several months, we had a natural sample of another planetary system passing through the neighborhood. Then it headed back out, never to return.
23. 🧲 A pulsar's timing can rival atomic clocks
Millisecond pulsars can spin hundreds of times a second with extraordinary long-term stability. Their rotation is so predictable that astronomers can calculate when pulses should arrive years into the future.
They aren't perfectly regular. Stellar motion, interstellar plasma, glitches and other effects all have to be modeled. But the best of them are extraordinarily precise astrophysical clocks, precise enough for experiments ranging from searches for gravitational waves to tests of general relativity.
They've even inspired pulsar navigation, where a spacecraft works out its position from X-ray pulsars somewhat as a receiver on Earth uses GPS satellites. NASA's SEXTANT experiment demonstrated the idea aboard the International Space Station in 2017.
The galaxy comes with naturally occurring clocks: city-sized dead stars spinning in the dark, broadcasting navigation beacons across thousands of light-years.
24. 🌍 Earth's core is almost as hot as the Sun's surface
Earth's inner core reaches temperatures estimated at around 5,000–6,000°C, comparable to the visible surface of the Sun. Yet the inner core is solid.
The reason is pressure. At Earth's center it reaches roughly 360 gigapascals, which raises iron's melting point enough for the innermost material to crystallize.
Around it is the liquid outer core, where flowing, electrically conductive iron alloy helps generate Earth's magnetic field.
We infer all this mostly from seismic waves rather than direct samples; the deepest hole humans have drilled reaches only a tiny fraction of Earth's radius.
So thousands of kilometers beneath your bed tonight lies a metal sphere nearly as hot as a star's surface, and almost everything we know about it comes from listening to earthquakes pass through the planet.
25. 🌌 "Red and dead" galaxies can stop forming stars astonishingly early
Astronomers once expected galaxies in the early universe to be overwhelmingly busy forming stars.
The James Webb Space Telescope has strengthened the evidence for an unexpected population: massive quiescent galaxies that existed surprisingly early in cosmic history. They had already built large stellar populations and then sharply cut back or stopped forming stars while the universe was only a small fraction of its current age.
How? Possibilities include running out of gas, powerful feedback from active galactic nuclei, gravitational heating and environmental effects. The exact mechanisms are still an active area of research.
Their existence tells us that early galaxies didn't all mature gradually. Some apparently grew up extraordinarily fast, burned through a furious youth and went quiet while the universe itself was still young.
26. 🌙 Saturn's moon Iapetus has an enormous equatorial ridge
Iapetus is one of the Solar System's strangest moons.
Running along much of its equator is a mountainous ridge that reaches roughly 20 kilometers high in places, giving parts of Iapetus the look of a walnut.
How the ridge formed is still uncertain. One hypothesis says Iapetus once had a small moon or ring system whose material gradually spiraled inward and piled up along the equator. Other models involve tectonic processes from an earlier era when it spun faster.
Iapetus is also dramatically two-toned, with one hemisphere much darker than the other. It looks less like a simple icy moon than a world assembled from several unrelated astronomical mysteries.
27. 🔭 Astronomers have directly photographed planets orbiting other stars
Most exoplanets are detected indirectly, because their stars wobble or dim. But some have actually been directly imaged.
The HR 8799 system is a spectacular example: at least four giant planets orbit the young star at large distances. By observing the system repeatedly over the years, astronomers have watched the planets move along their orbits.
Direct imaging is brutally difficult, because stars vastly outshine their planets. Instruments use coronagraphs and sophisticated image processing to suppress the starlight, and young giant planets make easier targets because they still glow brightly in the infrared with heat left over from their formation.
These aren't artistic reconstructions of inferred planets. They're actual photons arriving from alien worlds themselves.
28. ⚛️ Cosmic rays can strike Earth with macroscopic energies packed into single particles
Most cosmic rays are ordinary atomic nuclei traveling at extraordinary speeds, but a few reach almost unimaginable energies.
The famous Oh-My-God particle, detected in 1991, carried roughly 3 × 10²⁰ electron volts. That's tens of joules, about the kinetic energy of a thrown baseball, concentrated into a single subatomic particle. Its speed differed from the speed of light by an almost inconceivably tiny amount.
Where such ultra-high-energy cosmic rays come from is still an important open question. Candidate accelerators include active galactic nuclei and other extreme environments.
Somewhere out there, nature runs particle accelerators that reach energies millions of times beyond those of humanity's Large Hadron Collider.
29. 🌀 The Sun doesn't sit still at the center of the Solar System
We casually say Earth orbits the Sun. More precisely, Earth and the Sun both orbit their common center of mass, or barycenter, and the same is true for every body in the Solar System.
Jupiter is so massive that the Sun–Jupiter barycenter lies just outside the Sun's visible surface. With all the planets pulling at once, the Solar System's barycenter wanders relative to the Sun, sometimes inside it and sometimes outside.
So, seen from the right outside frame, the Sun traces a complicated wobble instead of sitting perfectly still while the planets circle it. The same principle lets astronomers detect exoplanets through stellar radial velocities.
Planets don't merely orbit stars. They make their stars move too.
30. 🌌 A sea of neutrinos from the Big Bang should surround you right now
About one second after the Big Bang, the universe became transparent to neutrinos, and those particles have been traveling ever since.
So cosmological theory predicts a cosmic neutrino background, like the cosmic microwave background but far older. Today these primordial neutrinos should have a temperature of around 1.95 kelvin, with hundreds of them in every cubic centimeter once all the neutrino and antineutrino types are counted.
They're extraordinarily hard to detect directly because neutrinos interact so weakly. Experiments have been proposed to catch them, but no widely accepted direct detection exists yet. Their existence is still strongly supported indirectly, by cosmological observations and well-tested early-universe physics.
If the standard cosmological picture is right, your bedroom tonight is full of particles that have been traveling freely for almost the entire 13.8-billion-year history of the universe.
🌙 One last thing before sleep
Looking into space has a curious consequence: you have never seen the Sun exactly as it is now. You see it as it was about eight minutes ago.
You see Jupiter as it was tens of minutes in the past. Sirius is about 8.6 years behind the present. Andromeda appears as it was roughly 2.5 million years ago. For distant enough galaxies, the delay stretches to billions of years.
So there's no single snapshot of "the universe right now" available to us. Every direction is a different depth in time.
Tonight's sky isn't really a ceiling dotted with objects at different distances. It's an archive. Whenever you look up, your eyes are taking in pages from thousands of different chapters of cosmic history at once.
That's all for tonight. Thanks for reading along. Good night, and may your skies be clear. 🌌
— Kasi