Stellar physics
How stars rotate, generate magnetic fields, evolve and leave compact remnants.
11 problemsAstrophysics
Stars, compact objects, and signals from space.
Explore Astrophysics
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Browse collectionsThe observed universe
Unseen matter, cosmic expansion, energetic particles, and brief radio flashes.
40 problemsInside planets and stars
Composition, structure and internal dynamics of planets and stars.
37 problemsStellar explosions
How stars explode, what they leave behind, and where heavy elements form.
5 problemsA few problems to explore
28 totalDark matter
Bent light and galaxy motions reveal gravity that known stars and gas cannot fully explain. What supplies the additional mass?
Black hole information problem
If a black hole evaporates, how is the information about what fell into it represented in what comes out? The answer must reconcile quantum evolution with gravitational calculations.
Ultra-high-energy cosmic rays
Particles arrive at Earth with energies far beyond those reached by human accelerators. Which cosmic objects accelerate them, and by what process?
Fast radio bursts
Brief radio flashes arrive from across the universe. Magnetars can produce some of them, but what generates their intense emission and explains the range of observed bursts?
Coronal heating problem
The Sun’s outer atmosphere is much hotter than its visible surface. Which processes deliver and dissipate enough energy to maintain it?
Solar modelling problem
Measurements of the Sun’s composition and interior do not all agree with standard solar models. Which changes would make the different lines of evidence fit together?