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If so, how might the internal structure be probed?.Do black holes have an internal structure?.Gravitational singularities: Does general relativity break down in the interior of a black hole due to quantum effects, torsion, or other phenomena?.The infrared/TeV crisis: Lack of attenuation of very energetic gamma-rays from extragalactic sources.What is the origin of the Galactic Center GeV excess? Is it due to the annihilation of dark matter particles or a new population of millisecond pulsars?.Does this apply to all ULXs? How could such a system form and remain stable?
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Galaxy rotation problem: Is dark matter responsible for differences in observed and theoretical speed of stars revolving around the centre of galaxies, or is it something else?.Can the discrepancy between the curves be attributed to dark matter?
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Rotation curve of a typical spiral galaxy: predicted ( A) and observed ( B). Nature of KIC 8462852, commonly known as Tabby's Star: What is the origin of unusual luminosity changes of this star?.The Oh-My-God particle and other ultra-high-energy cosmic rays: What physical processes create cosmic rays whose energy exceeds the GZK cuttoff?.Fast radio bursts (FRBs): What causes these transient radio pulses from distant galaxies, lasting only a few milliseconds each? Why do some FRBs repeat at unpredictable intervals, but most do not? Dozens of models have been proposed, but none have been widely accepted.p-nuclei: What astrophysical process is responsible for the nucleogenesis of these rare isotopes?.Supernova: What is the exact mechanism by which an implosion of a dying star becomes an explosion?.What is the origin of the stellar mass spectrum? That is, why do astronomers observe the same distribution of stellar masses – the initial mass function – apparently regardless of the initial conditions?.How does the Sun produce strong southward pointing magnetic fields in solar coronal mass ejections that lead to geomagnetic storms? How can we predict solar and geomagnetic superstorms?.Why is the magnetic reconnection effect many orders of magnitude faster than predicted by standard models?.Why is the Sun's corona (atmosphere layer) so much hotter than the Sun's surface?.What caused the Maunder Minimum and other grand minima, and how does the solar cycle recover from a minimum state?.How do other solar-like stars generate their magnetic fields, and what are the similarities and differences between stellar activity cycles and that of the Sun?.How does the Sun generate its periodically reversing large-scale magnetic field?.Is it the result of material (either from the rings of Saturn or its own ring) that over time collected upon the surface?.Is it the remnant of hot and fast-rotating young Iapetus?.What is the origin of chain of high mountains that closely follows the equator of Saturn's moon of Iapetus?.What is the true rotation rate of Saturn's deep interior?.Why does the magnetosphere of Saturn rotate at a rate close to that at which the planet's clouds rotate?.What is the explanation for the elongated orbits of a group of Kuiper belt objects?.How does accretion form planetary systems?.Is it because of our lack of data, given the difficulty of observing exoplanets? Or can it be explained by the grand tack hypothesis? Systems with Jupiter-like planets in Jupiter-like orbits appear to be rare. How unusual is our Solar System? Some observed planetary systems contain Super-Earths and Hot Jupiters that orbit very close to their stars (even closer than Mercury).