Tree of the Cosmosfrom the inflaton field to galaxies

Real basis

• Inflaton field: A hypothetical scalar field whose stored energy drove inflation. It has not been detected directly.

• Primordial gravitational waves: Ripples in spacetime predicted by inflation, which would leave a distinctive pattern in the polarization of the cosmic microwave background. A team announced a detection in 2014, but it turned out to be interference from Milky Way dust.

• Quark–gluon plasma: The state of the universe in its first few microseconds: hotter than 2 trillion degrees, with quarks and gluons not yet confined inside protons and neutrons.

• Baryogenesis: Some process, still unknown, left matter outnumbering antimatter by about one part in a billion. That small remainder makes up everything today.

• Big Bang nucleosynthesis: About 3 to 20 minutes after the Big Bang, the universe made hydrogen, helium and a little lithium. It was the universe's first “element furnace”.

• Recombination: The universe cooled to about 3,000 K, electrons were captured by nuclei, and the first neutral atoms formed.

• Cosmic microwave background: The light released at recombination has traveled to this day, stretched by cosmic expansion into microwaves at about 2.7 K.

• Dark matter halos: Dark matter first clumped under gravity, then ordinary gas fell into these gravity wells. These were the seeds of galaxies.

• Cosmic reionization: Ultraviolet light from the first stars and galaxies re-ionized the diffuse neutral hydrogen, and the universe became transparent.

• Cosmic ray: High-energy particles accelerated by supernova remnants. They smash carbon, nitrogen and oxygen nuclei, producing the universe's beryllium and most of its boron.

• Protostars: An embryonic star formed by a collapsing gas cloud. It has not begun hydrogen fusion yet and shines by releasing gravitational energy as it contracts.

• Population III stars: The first generation of stars, made almost entirely of hydrogen and helium, possibly hundreds of times the Sun's mass and living only a few million years. None has been observed directly yet.

• Blue giant: Massive O- and B-type stars with surface temperatures of tens of thousands of degrees and luminosities up to hundreds of thousands of times the Sun's, but only enough fuel to burn for a few million years.

• Red supergiant: The late life of a massive star. Betelgeuse is a red supergiant; placed where the Sun is, its surface would extend beyond the orbit of Mars.

• Wolf–Rayet stars: Extremely hot massive stars whose powerful stellar winds have stripped off the outer hydrogen, exposing the helium and carbon inside.

• Core-collapse supernova: A massive star's iron core collapses and the star explodes as it rebounds. Oxygen, neon, magnesium, silicon, sulfur, calcium and other elements come mainly from here.

• Neutron star: The core left behind by a supernova, only about 20 km across; a teaspoon of its matter weighs billions of tonnes.

• Stellar-mass black hole: When the most massive stars die, their cores collapse into black holes. In 2015, gravitational waves let us directly “hear” two such black holes merge for the first time.

• Red giant: After a Sun-like star uses up the hydrogen in its core, it swells into a red giant and fuses three helium nuclei into carbon in its core.

• Asymptotic giant branch stars: The final stage of low-mass stars. Inside, the slow neutron-capture process makes strontium, barium, lead and other elements, which stellar winds blow into space.

• Pulsars: A rapidly spinning neutron star that sweeps radio waves around like a lighthouse. The fastest pulsars spin more than 700 times per second.

• Planetary nebula: A glowing shell of gas thrown off by a star, nothing to do with planets. The name comes from how they looked like planetary disks in early telescopes.

• White dwarf: The remnant of a Sun-like star: the size of Earth but with about the Sun's mass, slowly cooling over tens of billions of years.

• Magnetar: The most strongly magnetized objects, with fields more than a quadrillion times Earth's.

• Nova: A white dwarf pulls in hydrogen from a companion star, the surface suddenly undergoes a nuclear explosion and brightness jumps by more than ten thousand times, but the white dwarf itself survives.

• Type Ia supernovae: A white dwarf explodes entirely once its mass exceeds about 1.4 solar masses. More than half the iron in the Solar System may come from here. They are also the “standard candles” used to measure cosmic expansion.

• Neutron star mergers: Two neutron stars collide, making heavy elements such as gold, platinum and uranium through rapid neutron capture. In 2017, humans observed both its gravitational waves and its light for the first time.

• Kilonova: The glowing afterglow of a neutron star merger, about a thousand times as bright as a nova, with freshly made heavy elements in its spectrum.

• Red dwarf: The most common stars in the Milky Way, with a fraction of the Sun's mass. They can live trillions of years, far longer than the universe's current age.

• Sun-like star: A yellow dwarf with a surface at about 5,800 K and a lifespan of about 10 billion years. The Sun is one ordinary member.

• Brown dwarf: “Failed stars” without enough mass to ignite hydrogen fusion, between giant planets and stars.

• Binary star system: About half of Sun-like stars have a companion. Mass transfer between the two stars gives rise to novae, Type Ia supernovae and X-ray binaries.

• Cepheid variable: Brightness pulses with a fixed period; the longer the period, the brighter the star. This rule, found by Leavitt in 1912, let Hubble measure the distances of galaxies.

• X-ray binary: When a compact object devours its companion, the accretion disk is heated to millions of degrees and emits X-rays. Cygnus X-1 was the first confirmed black hole candidate.

• Globular cluster: A ball of hundreds of thousands of ancient stars packed tightly together, up to more than 12 billion years old, older than most of the Milky Way's structure.

• Dwarf galaxy: Small galaxies with only hundreds of millions to a few billion stars and an especially high share of dark matter; the “building blocks” of large galaxies.

• Supermassive black hole: Almost every large galaxy has one at its center, with millions to billions of times the Sun's mass. Why they grew so fast in the early universe is still a puzzle.

• Quasars: Light emitted as a supermassive black hole feeds frantically. A quasar can outshine the whole Milky Way by hundreds of times.

• Active galactic nucleus: A supermassive black hole that is feeding, with jets that can extend hundreds of thousands of light-years beyond the galaxy.

• Protogalaxy: Young, gas-rich galaxies in the early universe, forming stars furiously. The Webb telescope saw them just a few hundred million years after the universe began.

• Galaxy merger: Galaxies grow through collisions. Mergers trigger large-scale star formation and can turn spiral galaxies into elliptical ones.

• Starburst galaxy: They form stars at tens to hundreds of times the Milky Way's rate, usually triggered by mergers or strong interactions.

• Elliptical galaxy: Formed by major mergers; their gas is used up, they barely form stars any more, and they are full of old red stars.

• Irregular galaxy: Galaxies with no clear shape; the Large and Small Magellanic Clouds are examples, often distorted by gravitational disturbances.

• Spiral galaxy: Disk galaxies where new stars are constantly born along the spiral arms; about 60% of large galaxies are of this type.

• Barred spiral galaxy: It has a “bar” of stars across its center; the Milky Way is one of them.

• Milky Way: About 100,000 light-years across, with 100 to 400 billion stars. The Sun sits on a minor spiral arm and circles the center once every 230 million years.

• Sagittarius A*: The supermassive black hole at the center of the Milky Way, about 4 million solar masses. The Event Horizon Telescope published its image in 2022.

• Density wave: Spiral arms are not fixed matter but slowly rotating “traffic jams”; stars passing through are squeezed and new stars form.

• Open cluster: Hundreds to thousands of young stars born from the same cloud of gas, such as the Pleiades, which gradually disperse within a few hundred million years.

• Galaxy group: Dozens of galaxies bound together by gravity; the smallest kind of galaxy collection.

• Local Group: A family of the Milky Way, the Andromeda Galaxy and about 80 small galaxies, about 10 million light-years across.

• Galaxy cluster: Thousands of galaxies gathered together, with gas at tens of millions of degrees between them; most of the mass is dark matter.

• Supercluster: A larger structure made of galaxy clusters, stretching over 100 million light-years and not entirely bound by gravity.

• Gravitational lens: Massive objects bend light, distorting, magnifying or even multiplying the images of galaxies behind them. It can be used to “weigh” dark matter.

• Filaments: Galaxies line up along giant threadlike structures that can be hundreds of millions of light-years long.

• Cosmic void: Empty regions over 100 million light-years across with very few galaxies, taking up most of the universe's volume.

• Laniakea Supercluster: The supercluster containing the Milky Way, mapped in 2014. Its name means “immeasurable heaven” in Hawaiian, and it contains about 100,000 galaxies.

• Cosmic web: A three-dimensional network of filaments, walls, nodes and voids: how the universe looks on the largest scales.

• Baryon acoustic oscillations: Sound waves in the early universe left a characteristic spacing of about 500 million light-years in the distribution of galaxies, a ruler for measuring cosmic expansion.

• Dark energy: Starting about 5 billion years ago, cosmic expansion switched from decelerating to accelerating. Whatever drives it is called dark energy, about 70% of the universe's total energy.

• Protoplanetary disk: A rotating disk of gas and dust around a newborn star. The Atacama Large Millimeter Array has photographed rings and gaps in the disk cleared by planets.

• Calcium-aluminum-rich inclusions: The oldest solids in meteorites, about 4.567 billion years old, taken as time zero of the Solar System.

• Chondrules: Tiny beads of rock flash-melted and cooled in the protoplanetary disk. Most meteorites contain them.

• Sun: Holds 99.86% of the Solar System's mass and converts about 4 million tonnes of mass into energy every second.

• Solar wind: A constant stream of charged particles from the Sun. It blows out past a hundred astronomical units before it meets the interstellar medium.

• Planetesimals: Kilometer-sized lumps of rock and ice, built up step by step from dust. They are the building blocks of planets.

• Jupiter: More than twice the mass of all the other planets combined. It probably formed first, and its gravity shaped the whole Solar System.

• Asteroid belt: Its total mass is only about 3% of the Moon's. Jupiter's gravity kept it from ever forming a planet.

• Saturn: Its average density is lower than water's. The rings are mostly ice chunks and may be only a few hundred million years old.

• Grand Tack hypothesis: One model says Jupiter once migrated inward to near Mars's orbit before Saturn “pulled” it back out. That could explain why Mars is so small.

• Uranus: Its rotation axis lies almost on its side, probably the result of a giant impact early on.

• Neptune: In 1846 its position was first predicted by mathematics, then confirmed with a telescope.

• Mercury: The planet closest to the Sun. One solar day there lasts about 176 Earth days, longer than its year.

• Venus: A thick carbon dioxide atmosphere causes a runaway greenhouse effect. The surface is about 465°C, hotter than Mercury.

• Earth: The only known planet with life, and the densest planet in the Solar System.

• Mars: It once had rivers and lakes. Curiosity found sedimentary rock from an ancient lake in Gale Crater.

• Ceres: The largest object in the asteroid belt. Dawn found bright salt deposits in its craters.

• Moon: Probably formed from material thrown out when Theia hit Earth. It stabilizes Earth's rotation axis and raises the tides.

• Earth's magnetic field: Flowing iron in the liquid outer core generates a magnetic field that blocks the solar wind and protects the atmosphere and oceans.

• Primordial atmosphere: The early atmosphere was mostly carbon dioxide, nitrogen and water vapor, with almost no oxygen.

• Kuiper belt: A belt of icy bodies beyond Neptune's orbit. In 2019 New Horizons flew past one of them, Arrokoth.

• The Nice model: The giant planets' orbits once went through an unstable rearrangement that threw many small bodies into the inner Solar System, possibly triggering the Late Heavy Bombardment.

• Pluto: Reclassified as a dwarf planet in 2006. New Horizons found that its “heart-shaped” region is a plain of nitrogen ice.

• Oort cloud: A spherical cloud of icy bodies surrounding the Solar System, possibly extending beyond 1 light-year. Long-period comets come from here.

• Comets: A “dirty snowball”. Rosetta detected glycine and phosphorus on comet 67P.

• Plate tectonics: The crust is broken into slowly moving plates that cycle carbon into the mantle and regulate Earth's climate over the long term.

• Deep-sea vents: Hot water rich in hydrogen and sulfides vents from the seafloor. Discovered only in 1977, they host whole ecosystems that live without sunlight.

Related research

These studies relate to this topic but are not direct proof of this page.

• The αβγ paper: Alpher and Gamow calculated how light elements formed in the Big Bang, and Bethe's name was added to make “αβγ.”

  Source: Alpher, Bethe & Gamow, Physical Review 1948, "The origin of chemical elements"

• Cosmic microwave background: Two Bell Labs researchers couldn't get rid of the noise in their antenna, and finally realized it was the afterglow of the Big Bang. They won the 1978 Nobel Prize.

  Source: Penzias & Wilson, The Astrophysical Journal 1965, "A measurement of excess antenna temperature at 4080 Mc/s"

• Explaining the afterglow: A Princeton team was preparing to look for this radiation, got scooped by the lab next door, and wrote down the theoretical explanation.

  Source: Dicke, Peebles, Roll & Wilkinson, The Astrophysical Journal 1965, "Cosmic black-body radiation"

• A perfect blackbody: The spectrum measured by COBE matched the theoretical blackbody curve almost perfectly, giving decisive support to Big Bang theory.

  Source: Mather et al., The Astrophysical Journal Letters 1990, "A preliminary measurement of the cosmic microwave background spectrum by the Cosmic Background Explorer (COBE) satellite"

• Ripples in the afterglow: The background radiation has temperature ripples of one part in 100,000. These tiny differences became the seeds of galaxies.

  Source: Smoot et al., The Astrophysical Journal Letters 1992, "Structure in the COBE differential microwave radiometer first-year maps"

• Baryon acoustic oscillations: Sound waves in the early universe left a characteristic scale of about 500 million light-years in the distribution of galaxies, which became a ruler for measuring the universe.

  Source: Eisenstein et al., The Astrophysical Journal 2005, "Detection of the baryon acoustic peak in the large-scale correlation function of SDSS luminous red galaxies"

• The 21 cm line: The first detection of 21 cm radio emission from neutral hydrogen let humans “see” gas in the Milky Way that is otherwise invisible.

  Source: Ewen & Purcell, Nature 1951, "Observation of a line in the galactic radio spectrum"

• Signal of the cosmic dawn: The EDGES experiment reported a 21 cm absorption signal left by the first stars, but the result is still disputed and awaits independent verification.

  Source: Bowman et al., Nature 2018, "An absorption profile centred at 78 megahertz in the sky-averaged spectrum"

• The atomic nucleus: Alpha particles occasionally bounced back off gold foil, and Rutherford concluded that an atom's mass is concentrated in a tiny nucleus.

  Source: Rutherford, Philosophical Magazine 1911, "The scattering of α and β particles by matter and the structure of the atom"

• What powers the stars: Bethe calculated that stars shine by nuclear fusion, solving the puzzle of how the Sun can burn for billions of years.

  Source: Bethe, Physical Review 1939, "Energy production in stars"

• Invisible mass: The outskirts of the Andromeda galaxy rotate too fast, so a large amount of unseen matter must supply the gravity. Dark matter was no longer just a guess.

  Source: Rubin & Ford, The Astrophysical Journal 1970, "Rotation of the Andromeda Nebula from a spectroscopic survey of emission regions"

• First proposal of dark matter: Zwicky found that galaxies in the Coma Cluster moved too fast and proposed that “dark matter” exists. The idea was ignored for decades.

  Source: Zwicky, Helvetica Physica Acta 1933, "Die Rotverschiebung von extragalaktischen Nebeln"

• Bullet Cluster: After two galaxy clusters collided, the gas stayed in the middle while the centers of gravity ended up on either side. Dark matter had been “flung” out.

  Source: Clowe et al., The Astrophysical Journal Letters 2006, "A direct empirical proof of the existence of dark matter"

• Shadow of a black hole: Radio telescopes around the world formed an Earth-sized “virtual telescope” and photographed the shadow of the black hole at the center of M87.

  Source: Event Horizon Telescope Collaboration, The Astrophysical Journal Letters 2019, "First M87 Event Horizon Telescope Results. I. The shadow of the supermassive black hole"

• Gravitational waves: Two black holes merged 1.3 billion years ago, and ripples in spacetime were finally heard by humans, confirming Einstein's prediction from a century earlier.

  Source: Abbott et al. (LIGO & Virgo), Physical Review Letters 2016, "Observation of gravitational waves from a binary black hole merger"

• The Chandrasekhar limit: A white dwarf has a maximum mass, about 1.4 solar masses. Beyond it, the star is doomed to keep collapsing.

  Source: Chandrasekhar, The Astrophysical Journal 1931, "The maximum mass of ideal white dwarfs"

• Giant black hole in the early universe: When the universe was under 700 million years old, there was already a black hole of 800 million solar masses. How did it grow so fast? Still a mystery.

  Source: Bañados et al., Nature 2018, "An 800-million-solar-mass black hole in a significantly neutral Universe at a redshift of 7.5"

• The Galactic center: Tracking stars near the galactic center for over a decade proved a black hole of about 4 million solar masses hides there. Nobel Prize 2020.

  Source: Ghez et al., The Astrophysical Journal 2008, "Measuring distance and properties of the Milky Way's central supermassive black hole with stellar orbits"

• B²FH: This hundred-page paper explained, step by step, how stars forge the elements of the periodic table. We are all stardust, and this is where that idea starts.

  Source: Burbidge, Burbidge, Fowler & Hoyle, Reviews of Modern Physics 1957, "Synthesis of the elements in stars"

• Hoyle's prediction: For stars to make enough carbon, Hoyle predicted that carbon-12 must have a special energy level, which experiments then confirmed.

  Source: Hoyle, The Astrophysical Journal Supplement 1954, "On nuclear reactions occurring in very hot stars. I. The synthesis of elements from carbon to nickel"

• Kilonova: The first time the same cosmic event was both “heard” and “seen”: the merger of two neutron stars.

  Source: Abbott et al., Physical Review Letters 2017, "GW170817: Observation of gravitational waves from a binary neutron star inspiral"

• Where gold comes from: The material thrown out by neutron star mergers contains large amounts of heavy elements. The gold on your ring probably came from such a collision.

  Source: Kasen et al., Nature 2017, "Origin of the heavy elements in binary neutron-star mergers from a gravitational-wave event"

• Pulsars: Graduate student Jocelyn Bell noticed a radio signal precise to the second. At first jokingly called “little green men,” it turned out to be a neutron star.

  Source: Hewish, Bell et al., Nature 1968, "Observation of a rapidly pulsating radio source"

• A galaxy at redshift 14: The Webb telescope confirmed bright galaxies that already existed about 300 million years after the universe began, much earlier than expected.

  Source: Carniani et al., Nature 2024, "Spectroscopic confirmation of two luminous galaxies at a redshift of 14"

• Hubble Deep Field: Hubble stared at a small patch of “empty” sky for ten days of exposure and captured about three thousand galaxies.

  Source: Williams et al., The Astronomical Journal 1996, "The Hubble Deep Field: Observations, data reduction, and galaxy photometry"

• Gaia star map: The Gaia satellite measured the positions and motions of over a billion stars, producing the most detailed 3D map of the Milky Way.

  Source: Gaia Collaboration, Astronomy & Astrophysics 2018, "Gaia Data Release 2. Summary of the contents and survey properties"

• Cold dark matter: If dark matter is “cold” and slow-moving, galaxies gather bottom-up step by step, which matches observations.

  Source: Blumenthal, Faber, Primack & Rees, Nature 1984, "Formation of galaxies and large-scale structure with cold dark matter"

• The shape of dark matter halos: Computer simulations show that cold dark matter halos, from dwarf galaxies to galaxy clusters, all follow the same density profile. The profile was later named after its three authors.

  Source: Navarro, Frenk & White, The Astrophysical Journal 1996, "The structure of cold dark matter halos"

• Recipe of the universe: The Planck satellite measured the tiny fluctuations in the cosmic microwave background: ordinary matter makes up about 5% of the Universe's total energy, dark matter about 27%, and the rest is dark energy.

  Source: Planck Collaboration, Astronomy & Astrophysics 2020, "Planck 2018 results. VI. Cosmological parameters"