The UniverseAnswer
Can a Planet Orbit Two Stars?
Two stars can circle each other while a planet travels around them both. Astronomers confirmed it by watching the moving stars dim.
THE QUESTION LIBRARY THE UNIVERSE
How did dark matter shape galaxies and the cosmic web?
How dark matter helped form the cosmic web and galaxies, and why comparing dwarf galaxies with clusters tests possible self-interactions.
THE SHORT ANSWER
Dark matter helped shape structure through gravity. Its detailed particle behavior remains uncertain: whether dark particles scatter appreciably off one another is an open question. Comparing galaxies and clusters helps test explanations across environments. Broad agreement about a formation picture does not settle every proposed microscopic mechanism.
- The cosmic web is a gravitational structure, not a literal material net.
- Removing dark matter changes the standard formation history.
- Velocity-dependent scattering is a hypothesis tested across environments.
WHAT WE DON’T KNOW YET
The microscopic dark-matter identity and scattering law remain unknown. Galaxy-scale inferences depend on ordinary-matter effects and modeling.
WHAT WOULD CHANGE THIS ANSWER
Independent cross-scale observations that distinguish self-interactions from competing explanations and match a specific particle model.
Dark matter helped shape structure through gravity. Its detailed particle behavior remains uncertain: whether dark particles scatter appreciably off one another is an open question. Comparing galaxies and clusters helps test explanations across environments. Broad agreement about a formation picture does not settle every proposed microscopic mechanism.
THE LONG ANSWER
THE LONG ANSWER · ABOUT 2 MINUTES
You’ve read your 3 free long answers this month.
The short answer, how sure we are, what we don’t know, what would change our mind and every source stay free on every page, for everyone.
All Access members read the long answer: the evidence piece by piece, the strongest objections, and how to check it yourself.
Join All Access · $1 a week Or $6 a month
Billed $52 once a year. Cancel anytime in your account.
Until December 4, 11:59 pm Pacific: the Founding rate is $39 a year, and it stays $39 while you stay a member.
Create a free account: 6 long answers a month, email only.
Paying never buys a different answer. Our Paywall Promise
Keep asking
New here?
God Plays Dice answers big questions in plain words, with sources and one of six honest labels.
Words worth knowing (3)
- halo
- The extended matter distribution surrounding a galaxy or cluster.
- self-interaction
- An interaction among dark particles themselves beyond their common gravity.
- mediator
- A particle that carries an interaction in a proposed model.
Sources & further reading
(4) · Checked Oct 5, 2026
- History of cosmic structure formation ↗European Space AgencyOfficial formation explanation; cold-component clumping and later ordinary-gas infall.
- NASA Reveals New Details About Dark Matter's Influence on Universe ↗NASA Jet Propulsion LaboratoryWebb formation report; dark component encourages earlier galaxy formation, not proof of every counterfactual.
- Beyond Collisionless Dark Matter: Particle Physics Dynamics for Dark Matter Halo Structure ↗Tulin, Yu and Zurek; Physical Review D2013 original light-mediator scattering model with nontrivial velocity dependence.
- Velocity-dependent Self-interacting Dark Matter from Groups and Clusters of Galaxies ↗Sagunski and colleagues; Journal of Cosmology and Astroparticle Physics2021 published analysis, preprint 2020; mild model-dependent preference and systematic-effect checks.
See a mistake? Report a problem. Corrections are made openly.
CONTINUE THE THREAD
Where this question leads.
The UniverseAnswer
What Is the Higgs Field, and Why Call Its Particle the “God Particle”?
An everywhere-present field, a fleeting particle and a famous nickname. What did CERN’s experiments actually measure?
The UniverseAnswer
Why do physicists still call the matter-antimatter imbalance unsolved?
Why the matter surplus remains unexplained, what Sakharov's conditions require, and how sphalerons and proposed neutrino mechanisms might connect.