Science labs › Earth and space › Galaxy Formation
A spinning cloud of stars and gas pulls itself together. Ball or plate?
Galaxy Formation lab · Last updated: 16 October 2026
You watch a huge spinning cloud of stars and gas pull itself together under its own gravity and predict what shape it will become: a ball or a flat plate. It is the same story that built our own Milky Way, a flat spiral disc, and it shows how gravity and spin work together.
What you'll discover
- Gravity pulls a cloud of gas and stars inwards, making it smaller and denser.
- As a spinning cloud shrinks it spins faster, and the spin stops it collapsing sideways.
- Gas settles into a flat, spinning disc, while stars that formed early can stay in a rounder shape.
The science in plain words
Galaxies began as enormous clouds of gas and dark matter in the young universe. Every part of a cloud pulls on every other part through gravity, so slightly denser regions pull in more material and slowly collapse. As the gas falls inwards and becomes denser, stars begin to form inside it.
Almost every cloud has some spin. As it shrinks, it spins faster, like an ice skater pulling in their arms. This is called conservation of angular momentum. The spin makes it hard for material to fall in towards the axis from the side, but nothing stops it falling along the direction of the axis. Gas clouds also collide with each other and lose energy as heat, so the gas gradually settles into a thin, flat, rotating disc. New stars form in that disc, which is why spiral galaxies like the Milky Way look like a flat plate with a bulge in the middle.
Stars behave differently from gas. They almost never collide, so stars that formed before the disc settled keep their tilted orbits and make a rounder halo. Galaxies built mainly from old stars, often after galaxies merge, can end up as round or oval elliptical galaxies. So the answer depends on how much gas there is and when the stars formed.
Where it fits
- India, NCERT: Goes beyond the NCERT syllabus for classes 6 to 10; it builds on Class 6 Beyond Earth and Class 9 Gravitation.
- United States: Grades 6 to 12
- Next Generation Science Standards: MS-ESS1-2
Common questions
How are galaxies formed?
Galaxies formed from huge clouds of gas and dark matter in the early universe. Gravity pulled the material together, and as the gas became denser it formed stars. Over billions of years galaxies have also grown by pulling in more gas and merging with smaller galaxies nearby.
Why is the Milky Way flat?
The gas that formed the Milky Way was spinning. As it collapsed, the spin stopped it falling inwards from the sides, but it could still flatten along the spin axis. Colliding gas lost energy and settled into a thin rotating disc, where most of its stars formed.
What shapes can galaxies be?
Astronomers group galaxies into three main shapes: spiral galaxies with flat discs and arms, like the Milky Way; elliptical galaxies, which are round or oval and mostly hold older stars; and irregular galaxies with no clear shape, often disturbed by a neighbour's gravity.
Related labs
- Orbital Mechanics: Newton's cannonball: how fast must you fire it sideways so it never lands?
- Star Life Cycle: Heavy stars have more fuel. So why do they die young?
- Black Holes: Shine light past a black hole: does it bend, or fall in for ever?
See all earth and space labs or every Taz science lab.
Try it yourself
The Galaxy Formation lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.