Cosmic Simulator — Build and Evolve a Universe

About the Game

Cosmic Simulator is an interactive 2D universe sandbox. Begin with a reproducible Big Bang, then watch matter move through dark-matter halos, cluster under gravity, ignite as stars, form planetary systems, and return to space through supernovae. The model is scientifically inspired rather than a precise astrophysics calculation.

Features

• Seeded universes with adjustable primordial gas, expansion, gravity, dark-matter balance, and initial speed.
• Emergent star formation from dense matter, accelerated stellar lifecycles, layered supernova shocks, metal-rich gaseous ejecta, expanding nebulae, neutron stars, pulsars, and black-hole remnants.
• Quasars that ignite when a supermassive black hole actively feeds at a galactic center.
• Simplified planet formation and orbital motion around stars.
• Pan, zoom, object selection, detailed inspection, and clickable cosmic event history.
• Experimental tools to add matter, stars, or black holes to the same running simulation.
• Optional labels, orbit paths, gravity vectors, dark-matter halos, velocities, and density layers.
• Local Save and Load for the current universe.
• Three experimental dark-matter models: cold/WIMP-like, warm, and self-interacting.

Controls

• Start Big Bang: Creates the configured universe and begins cosmic time.
• Drag / mouse wheel: Pan and zoom. Double-click an object to focus it.
• Select: Choose a halo, star, planet, black hole, cluster, or nebular remnant and inspect its properties. Galaxy labels describe derived member systems rather than standalone objects.
• Matter / Star / Hole / Neutron: Add an experiment at the selected point in space. The Neutron tool can create an ordinary neutron star or a beamed pulsar.
• Remove: Delete the selected object under the pointer.
• Pause and speed controls: Stop time or accelerate it from 1× to 1M×.
• Gravity controls: Experiment with gravity from 0.5× to 5×.
• Save / Load: Store or restore the current universe on this device.

Cosmic Simulator Experiment Guide

Use the same universe seed when comparing settings. A repeated seed keeps the initial density pattern consistent, making changes in expansion, gravity, matter balance, or dark-matter model easier to observe. Start at 1,000× or 10,000×, accelerate to 1M× while waiting for long-term evolution, and slow down or pause when an important event appears in the history.

1. Expansion versus gravitational collapse

1. Start a universe with Balanced expansion, 1× gravity, and the default matter balance. Save it after gas clouds become visible.
2. Reset with the same seed and choose Powerful expansion. Compare the number of dense gas clouds, stars, and galaxies.
3. Repeat with 1.5× gravity.

Watch for: Powerful expansion spreads gas and halo centers farther apart. Stronger gravity helps gas remain concentrated, increases encounters, and can accelerate the appearance of stars. Use the Density and Gravity Field layers to compare the competing effects.

2. Compare dark-matter models

Run the same seed once with each model: Cold / WIMP-like, Warm dark matter, and Self-interacting.

Watch for: Cold dark matter favors more concentrated small structures and satellite subhaloes. Warm dark matter suppresses some small-scale structure. Self-interacting dark matter creates softer central cores and settles differently. The enormous translucent regions are dark-matter haloes; the much smaller labeled galaxy boundaries are derived from their actual stars, planets, gas, and black holes.

3. Grow a galaxy inside a halo

Enable Labels, Dark Matter, and Matter Density. Follow a dense gas cloud inside a halo and raise the simulation speed.

Watch for: Gas must become both cool and dense before forming stars. A galaxy label appears only after multiple real stars share a host halo. As planets form around those stars, the label’s star and planet counts update. Galaxies are classifications of their members, not separate simulated bodies.

4. Recycle a supernova

Let a massive star age naturally, or place several stars close together to encourage a massive stellar collision. Pause when a supernova appears, then inspect the expanding remnant and resume at high speed.

Watch for: The initial flash is followed by shock fronts and a longer-lived nebula. Oxygen-, silicon-, iron-, and carbon-rich gas is thrown outward, heats and compresses nearby clouds, then cools. This enriched gas can later become part of new stars and makes rocky planets more likely.

5. Feed a black hole

Place a black hole near a gas cloud or a dense stellar region. Turn on the Gravity Field and reduce the speed when matter begins falling inward.

Watch for: Consumed gas, planets, and stars increase the black hole’s mass, event horizon, capture reach, and gravitational influence. A hot accretion disk can become X-ray bright; the black center itself does not emit that light. Very massive black holes are reclassified as supermassive.

6. Produce gravitational waves

Place two black holes near each other, preferably inside a dense central region, and let gravity bring them together.

Watch for: The pair merges into a more massive black hole while conserving their combined motion. Expanding cyan rings represent gravitational waves. The effect is visual and educational rather than a numerical general-relativity calculation.

7. Trigger stellar collisions

Place several stars within a compact region and increase gravity. Slow the simulation as their paths begin crossing.

Watch for: Stars can merge into a more massive star. A sufficiently massive or energetic collision can cause a supernova, return enriched gas to space, and leave a black hole.

8. Build a before-and-after observation

Save a universe before a major intervention. Add matter, a star, or a black hole; allow it to evolve; then record the statistics and event history. Load the save to repeat the experiment with one changed variable.

Useful measurements include gas particles, dense gas clouds, stars, planets, derived galaxies, dark haloes and subhaloes, galaxy clusters, nebulae, supernovae, black-hole mergers, and stellar collisions. Because the simulation is chaotic, compare broad outcomes rather than expecting every orbit or collision to repeat exactly after manual interaction.

9. Compare neutron stars and pulsars

Add several neutron stars, or evolve stars through supernovae, and slow the simulation to inspect the compact remnants.

Watch for: Every pulsar is a neutron star, but not every neutron star is shown as a pulsar. Pulsars sweep narrow polar beams through space as they rotate. Put two neutron stars close together to trigger a merger, a black-hole remnant, and gravitational waves.

10. Ignite a quasar

Let a central black hole grow beyond the supermassive threshold, then supply dense gas with the Matter tool.

Watch for: A bright accretion disk and extended bipolar jets appear while the black hole is feeding rapidly. The quasar is the active galactic nucleus powered by hot infalling matter; it is not a separate star and the black hole itself remains dark.

Understanding the visual layers

• Labels: Shows object identities and derived galaxy membership counts.
• Orbit lines: Shows stabilized planetary paths around surviving parent stars.
• Gravity field: Displays the direction and relative strength of local acceleration.
• Dark matter: Reveals the large halo envelopes and cosmic-web filaments.
• Velocity vectors: Shows the direction and relative speed of sampled gas clouds.
• Matter density: Highlights areas where gas is concentrated enough to approach star-forming conditions.

The simulator compresses astronomical distances and billions of years into a playable system. Use it to compare relationships and outcomes, not to obtain precise astronomical predictions.

News & Release Notes

September 26, 2026 — First cosmic light

• Create reproducible universes and experience a Big Bang that initializes the matter, motion, gravity, and dark-matter systems.
• Dense clouds can now produce stars; stars age, explode, return enriched matter to space, and can leave black holes.
• Planetary systems can form around stars, while experimental tools let you inject matter or place massive objects.
• Added time and gravity controls, pan and zoom, object inspection, event history, statistics, visualization layers, and local Save/Load.
• Dark-matter halos now expand with the early universe, cluster under their own gravity, and seed galaxy-scale concentrations of ordinary matter. They remain collisionless, while their central profiles can respond gradually to concentrated baryonic mass.
• Black holes exert a stronger local influence. Mergers conserve their combined motion, can build supermassive galactic-center objects, and send visible gravitational waves across space.
• Accreting black holes now brighten in X-rays from their superheated surrounding disks; the black event horizon itself does not emit light.
• Stars can collide and merge. Especially massive or energetic collisions can trigger a supernova and leave a compact remnant.
• A connected cosmic web now grows between dark-matter halos. Ordinary matter gathers along its filaments, and galaxy clusters emerge at dense intersections with hot X-ray gas and a growing central massive black hole.
• Dark-matter structure now begins with seeded density variations. Extended haloes grow through accretion and mergers, retain some satellite subhaloes, settle after expansion, and respond gradually to concentrated ordinary matter.
• Added cold/WIMP-like, warm, and self-interacting models. They change small-scale halo abundance, central concentration, core size, and settling behavior without simulating individual hypothetical particles.
• Gas now heats during halo collapse and must cool and compress before forming stars, while enriched gas cools more efficiently.
• Supernovae now launch asymmetric, composition-colored gas at high speed, drive layered shock fronts through nearby clouds, and leave long-lived expanding nebulae. Their enriched ejecta can cool into later stars and makes rocky planets more likely, while the shock can compress nearby gas enough to help trigger new star formation.
• Dark matter is now more abundant, gravitationally influential, visible by default, and dynamically pulsing as its moving haloes build the cosmic web. Primordial gas gathers into visible clouds inside those haloes, stars ignite from cooled halo gas, derived galaxies emerge from their actual stars, planets, gas, and black holes, and groups of those galaxies can become galaxy clusters. Supernova gas remains in this same cycle as enriched raw material for later stars and planets.
• Dark-matter haloes are now always at least five times wider than their luminous galaxy systems. Galaxies no longer render as separate spiral objects: their boundaries and labels are calculated from the positions of their actual member stars, planets, gas, and black holes. Stars, planets, and black holes are rendered at a smaller scale so the hierarchy remains legible.
• Dark-matter haloes and galaxy-cluster envelopes now appear ten times larger. Black holes gain event-horizon size, mass, capture reach, and gravitational influence as they consume gas, stars, and planets. Stellar size now varies more strongly with mass, and massive stars exert disproportionately stronger gravity than low-mass stars.
• Added a practical experiment guide covering expansion, gravity, dark-matter models, galaxy growth, supernova recycling, black-hole feeding, gravitational waves, stellar collisions, observation layers, and repeatable comparisons.
• Massive supernovae can now leave neutron stars, including pulsars with rotating polar beams. Neutron-star mergers can form black holes and send gravitational waves across the simulation.
• Actively feeding supermassive black holes can now ignite as quasars with brilliant accretion light and extended jets at galactic centers.

How the simulation works

Each visible gas point represents an enormous cloud rather than a literal particle. Dark-matter halos contribute gravity without colliding with ordinary matter. Gas is assigned to the halo that gravitationally hosts it; nearby dense, cool halo clouds aggregate into stars. Once several stars share a halo, the simulation derives a galaxy from those stars and their planets, gas, and black holes—it does not create a separate galaxy body. Massive stars burn through their compressed lifetimes quickly and may explode. Their ejecta rejoin the same gas system, so later stars, planets, galaxies, and clusters can incorporate material from earlier stellar generations.

This hierarchy follows NASA’s galaxy-evolution overview: galaxies grow around initially denser regions, contain stars and gas, commonly host central massive black holes, and evolve through star formation, collisions, and mergers. It also follows the galaxy-formation relationship described by the CSIRO Australia Telescope National Facility, with ordinary matter cooling inside much larger dark-matter haloes. Sizes remain intentionally compressed for playability rather than representing a literal astronomical scale.

The supernova model separates the brief explosion from its much longer aftermath. A luminous flash and expanding shock disturb surrounding matter, while oxygen-, silicon-, iron-, and carbon-rich gaseous ejecta form a cooling nebular remnant. This playable approximation follows NASA’s description of an expanding hot-gas nebula and the EBSCO overview of fast, element-rich ejecta and supernova remnants; see also NASA Space Place’s supernova explainer.

The large-scale structure follows the simplified relationship described by The Hunt for Galaxy Clusters: early variations grow into a cosmic web, and clusters form where filaments meet. Each displayed cluster represents many galaxy systems at an intentionally compressed scale. Its blue haze represents extended hot intracluster gas, while most of its simulated mass remains in the dark-matter halos.

Distances, masses, temperatures, and times are scaled for playability. Planetary orbits use stabilized Newtonian-style motion, and black holes use a capture radius rather than general relativity. In the visualization, X-ray brightness belongs to hot matter in an active accretion disk—not to the black hole itself, consistent with NASA’s overview of black holes.

Compact remnants follow the relationships summarized in Futurism’s comparison of neutron stars, pulsars, and quasars: neutron stars can remain after core-collapse supernovae, and a pulsar is a rotating neutron star whose polar radiation beams sweep through space. Quasars are modeled separately as temporary active states of feeding supermassive black holes at galactic centers, not as stellar remnants.

The selectable particle models are hypotheses, not detected substances. The cold option is WIMP-like and produces more concentrated small-scale structure; warm dark matter suppresses smaller haloes; self-interacting dark matter produces softer central cores. These bounded approximations follow the relationships reviewed in Dark Matter Haloes and Subhaloes, while avoiding a computationally prohibitive particle-level cosmological simulation.