Playground
Play with some interactive astronomy experiments and simulations! These are simplified, illustrative toy models, and some visual cues are exaggerated or added for clarity rather than being physically precise or necessary to the simulation.For the best performance, please use a desktop. On mobile, please allow experiments a moment to load.
Experiment 01
Black-Hole Growth Simulator
Test whether a black-hole seed can grow into an early-universe giant under a simple constant-Eddington-ratio accretion model.
Explanation
The dark sphere marks the region around the event horizon, and the tilted ring represents a hot accretion disk feeding the black hole. The drawing is stylized, with bright arcs added to make depth easy to read as you rotate it. Seed mass sets the starting point; the two redshifts set the available cosmic time; and accretion rate, duty cycle, and spin determine how quickly incoming matter adds to the black hole.
The graph follows cosmic time from left to right and uses a logarithmic mass scale, so each vertical step represents a tenfold increase. The moving dot shows the current mass, while the dashed 10⁹ M☉ line provides a useful early-quasar benchmark. Larger seeds, faster or more sustained feeding, and longer time intervals raise the final mass; rapid prograde spin can slow growth because more of the incoming matter's energy escapes as light.
- Seed mass
- The black hole's starting mass. Stellar remnants are often 10–100 M☉, while proposed direct-collapse seeds can reach 10⁴–10⁶ M☉.
- Accretion rate
- How quickly the black hole feeds. An Eddington ratio near 0.1 means slow feeding, 1 means rapid quasar-like feeding, and values above 1 explore extreme growth.
- Spin, a*
- How fast and in which direction the black hole rotates. Positive values turn with the disk, while negative values turn against it.
- Seed redshift
- When growth begins. A higher redshift means an earlier time in the universe.
- Observation redshift
- When growth ends in the simulation. A lower value gives the black hole more time to grow.
- Duty cycle
- The share of time spent feeding. A 50% duty cycle means the black hole feeds for half of the available time.
- Radiative efficiency
- The share of incoming matter released as light. Higher efficiency leaves less matter available to add to the black hole's mass.
- Variable presets
- Stellar seed begins small and early. Direct collapsebegins with a much larger seed. Rapid growth combines a large seed, fast feeding, and a high duty cycle.
These settings are simple examples. Real black holes can move between different growth patterns.
Drag to rotate in 3D
Drag the plot dot to inspect mass growth
- Time available
- 582 Myr
- Effective e-folding time
- 74 Myr
- Projected mass
- 2.52 × 10^8 M☉
Toy model: A flat ΛCDM expansion history converts the seed and observation redshifts into an elapsed growth time. The mass then grows exponentially with fixed accretion rate, duty cycle, spin, and spin-based radiative efficiency. Fuel shortages, feedback, mergers, and changing accretion states fall outside the calculation, so the result is best read as a controlled growth scenario for comparing assumptions.
Experiment 02
Stellar Evolution Explorer
Change a star's initial mass and follow its simplified path from the main sequence to its final remnant.
Explanation
A star's initial mass largely determines how brightly it shines, how quickly it uses its nuclear fuel, and which remnant it leaves behind. Press play, drag the timeline, or select a phase to follow that path. Because the main sequence occupies most of a star's life, the display begins five-sixths of the way through it; later phase markers are spaced evenly so brief events remain easy to inspect.
Sun-like stars swell into red giants, shed their outer layers as planetary nebulae, and leave white dwarfs. High-mass stars expand into red supergiants: they are substantially more massive, larger, and more luminous than ordinary red giants, despite having similarly cool, reddish surfaces. They then undergo core-collapse supernovae and leave neutron stars or black holes. Whether the remnant is a neutron star or black hole depends more directly on the mass of the collapsed core that remains after the supernova; the initial-mass thresholds used here are only a simplified proxy. The 1 M☉, 12 M☉, and 30 M☉ presets illustrate these three outcomes. Displayed sizes are not to scale; the stronger size, colour, and glow differences identify the two giant phases. Surface motion and pulsation are visual cues, and the neutron-star stage is shown as a pulsar whose sweeping beams happen to cross our line of sight.
Phases are evenly spaced for easy selection; playback slows through longer intervals. Drag to explore or select any phase.
- Main-sequence lifetime
- 10 Gyr
- Main-sequence luminosity
- 1.0 L☉
- Final remnant
- White dwarf
Toy model: For a single star with Sun-like composition, a few mass ranges set approximate luminosity, main-sequence lifetime, phase duration, and remnant type. Fixed thresholds send lower-mass stars to white dwarfs and higher-mass stars to neutron stars or black holes. Detailed nuclear burning, composition changes, winds, mass loss, rotation, and binary interactions can shift those boundaries in real stars.
Experiment 03
Gravitational Lensing Sandbox
Drag the background galaxy around a foreground lens and watch gravity split, stretch, and magnify its apparent image.
Explanation
Gravity from a foreground galaxy or cluster bends light from a more distant source galaxy. This sandbox gathers the foreground mass into the central marker, then shows the source's true position and the two places where its light appears to an observer. The dashed circle is the Einstein radius, the natural angular scale set by the lens mass and the distances between observer, lens, and source. Display units are arbitrary distances within this diagram, useful for comparing how the results change. The side view shows the line-of-sight order; its distances and light paths are schematic and unscaled.
Dragging the source toward the centre moves both images toward the Einstein radius, where they brighten and stretch into arcs; perfect alignment joins them into an Einstein ring. Increasing lens mass or the distance factor enlarges this bending scale, while source size changes the width of the drawn arcs. The point-source equation predicts unlimited magnification at exact alignment, so the display caps the readout at “> 40×.”
- Einstein radius
- 55.0 display units
- Total magnification
- 1.06×
- Image separation
- 156.8 display units
Toy model: An axisymmetric point-mass lens uses the scalar thin-lens equation to calculate the positions and magnifications of two point-source images. The source size and arc shapes are visual aids layered onto those solutions. Extended galaxies and clusters distribute mass unevenly, producing shear, multiple arcs, and other structures that require a full lens model.
Experiment 04
Orbital Resonance Toy
Choose one to five bodies and compare repeating period-ratio chains with a near-resonant pattern that keeps shifting over time.
Explanation
An orbital period is the time a body takes to complete one orbit, and a period ratio compares that time with a neighbour's. In a 2:1 pair, the inner body completes two orbits while the outer body completes one; in a 3:2 pair, they complete three and two. Adding more bodies repeats the chosen ratio between neighbours, so a five-body 2:1 chain has relative periods of 1:2:4:8:16.
Ratios made from small whole numbers return the entire chain to the same relative alignment after a predictable number of inner orbits, which appears in the repeat readout. The Near resonance preset uses slightly mismatched periods, so its geometry drifts without a short repeat. In a physical resonance, gravity also keeps a particular orbital-angle combination oscillating within a limited range, a behaviour called libration.
- Relative periods
- 1 : 2 : 4
- Pattern repeats after
- 4 inner orbits
- Inner-orbit phase
- 0.00 turns
Toy model: Non-interacting markers move at constant angular speeds along fixed, circular, coplanar tracks. The selected period ratios alone determine when their relative positions repeat, while the displayed orbit sizes are chosen for visual clarity. The calculation leaves out Kepler's third law, gravitational coupling, eccentricity, and the resonant-angle libration used to identify a true dynamical resonance.