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?
Stellar physics
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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?
Core-collapse supernova mechanism
The collapse of a massive star can launch an explosion. Which stars explode, and can models predict the explosion and remnant from the star’s pre-collapse structure?
Neutron-star equation of state
How does pressure depend on density inside a cold neutron star?
Type Ia supernova progenitors
Which white-dwarf systems produce the different Type Ia supernovae?
Solar dynamo
Where and how does the Sun regenerate the magnetic field underlying its activity cycle?
Multiple populations in globular clusters
Stars within one globular cluster can have different light-element abundances. Their common origin is still debated.
Pulsar radio emission
A pulsar’s rotating beam is familiar. The plasma process that makes its exceptionally bright radio waves is less certain.
Stellar angular momentum transport
A star’s core and outer layers exchange rotational motion. Which internal processes set that exchange as stars evolve?
Pulsar glitches
Some pulsars suddenly spin faster. What triggers the rapid transfer of rotational motion that produces a large glitch?
Common-envelope ejection
Two stellar cores can spiral through one shared envelope. What determines whether that gas escapes and how close the surviving binary becomes?