This article is a list of notable unsolved problems in astronomy. Problems may be theoretical or experimental. Theoretical problems result from current theories' inability of explaining observed phenomena or experimental results. Experimental problems result from inability to test or investigate a proposed theory. Other problems involve unique events or occurrences that have not repeated themselves with unclear causes.

Planetary astronomy

Our solar systems

Extra-solar

Stellar astronomy and astrophysics

  • Solar cycle:
    • How does the Sun generate its periodically reversing large-scale magnetic field?
    • How do other Sol-like stars generate their magnetic fields, and what are the similarities and differences between stellar activity cycles and that of the Sun?[6]
    • What caused the Maunder Minimum and other grand minima, and how does the solar cycle recover from a minimum state?
  • Coronal heating problem:
    • Why is the Sun's corona so much hotter than the Sun's surface?
    • Why is the magnetic reconnection effect many orders of magnitude faster than predicted by standard models?
  • Space weather prediction:
  • 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?[8]
  • Supernova: What is the mechanism by which an implosion of a dying star becomes an explosion?
  • p-nuclei: What astrophysical process is responsible for the nucleogenesis of these rare isotopes?
  • Fast radio bursts (FRBs): What causes these transient radio pulses from distant galaxies, lasting a few milliseconds each? Why do some FRBs repeat at unpredictable intervals but many others do not? Several models have been proposed but no one theory has become widely accepted.[9]
  • The Oh-My-God particle and other ultra-high-energy cosmic rays: What physical processes create cosmic rays whose energy exceeds the GZK cutoff?[10]
  • Nature of KIC 8462852, commonly known as Tabby's Star: What is the origin of the unusual luminosity changes of this star?

Galactic astronomy and astrophysics

Rotation curve of a typical spiral galaxy: predicted (A) and observed (B). Can the discrepancy between the curves be attributed to dark matter?
  • Galaxy rotation problem: Is dark matter (solely) responsible for differences in observed and theoretical speed of stars revolving around the center of galaxies?
  • Age-metallicity relation in the Galactic disk: Is there a universal age-metallicity relation (AMR) in the Galactic disk (both "thin" and "thick" parts of the disk)? In the local (primarily thin) disk of the Milky Way, there appears to be no evidence of a strong AMR.[11] A sample of 229 nearby "thick" disk stars has been used to investigate the existence of an age-metallicity relation in the Galactic thick disk and indicates that there is an age-metallicity relation present in the thick disk.[12][13] Stellar ages from asteroseismology confirm the lack of any strong age-metallicity relation in the Galactic disc.[14]
  • Ultraluminous X-ray sources (ULXs): What powers X-ray sources that are not associated with active galactic nuclei but exceed the Eddington limit of a neutron star or stellar black hole? Are they due to intermediate-mass black holes? Some ULXs are periodic, suggesting non-isotropic emission from a neutron star. Does this apply to all ULXs? How could such a system form and remain stable?
  • What is the origin of the Galactic Center GeV excess?[15] Is it due to the annihilation of dark matter particles or a new population of millisecond pulsars?
  • The infrared/TeV crisis: Lack of attenuation of very energetic gamma rays from extragalactic sources.[16][17][18]

Black holes

Cosmology

Estimated distribution of dark matter and dark energy in the universe

Extraterrestrial life

  • Is there other life in the Universe? Especially:
    • Is there other intelligent life?
    • Is there potentially an infinite amount of extraterrestrial genera throughout our universe? If so, what is the explanation for the Fermi paradox?[36][37]
  • Nature of Wow! signal:
    • Was this singular event a result of any extraterrestrial phenomenon? If so, what was its origin?[38]

See also

References

  1. See Planets beyond Neptune#Orbits of distant objects for details.
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