Gamma-ray bursts (GRBs) are the most energetic explosions in the universe, releasing more energy in seconds than our Sun will emit in its entire lifetime. These cataclysmic events, often associated with the collapse of massive stars or neutron star mergers, produce not only prompt gamma-ray emission but also long-lasting afterglows across multiple wavelengths. These afterglows serve as cosmic laboratories, offering unique opportunities to study fundamental physics—including potential interactions with dark matter.
Dark matter constitutes approximately 85% of the matter in the universe, yet its particle nature remains elusive. Unlike ordinary matter, dark matter does not emit, absorb, or reflect light, making it detectable only through gravitational effects. High-energy astrophysical phenomena, such as GRB afterglows, provide a rare window to probe non-gravitational interactions between dark matter and standard model particles.
The afterglow spectra of GRBs typically follow power-law decays attributed to synchrotron radiation from relativistic electrons. However, deviations from these expected spectra could hint at exotic physics, including dark matter interactions.
Several theoretical models propose mechanisms through which dark matter could influence GRB afterglow spectra:
WIMPs, a leading dark matter candidate, could interact with GRB photons via loop-level processes or mediator particles. For example, if WIMPs couple to photons through a dark photon, resonant absorption features might appear in the afterglow spectrum.
ALPs could convert to photons (and vice versa) in the presence of magnetic fields. GRB afterglows passing through galaxy clusters or filaments might exhibit energy-dependent oscillations due to ALP-photon mixing.
If dark matter consists of PBHs, their gravitational lensing effects could distort the temporal and spectral properties of GRB afterglows.
Detecting dark matter signals in GRB afterglows is a formidable task, requiring:
This exceptionally bright GRB provided some of the most stringent limits on photon-dark matter interactions. No significant deviations from standard afterglow models were found, constraining ALP couplings to <10-11 GeV-1.
The Fermi Gamma-ray Space Telescope has observed hundreds of GRBs, placing limits on dark matter annihilation cross-sections. For WIMP masses above 100 GeV, Fermi data rule out annihilation rates exceeding <10-25 cm3/s.
Next-generation observatories promise unprecedented sensitivity to dark matter signals in GRB afterglows:
The intersection of gamma-ray astrophysics and dark matter research is a rapidly evolving frontier. While no definitive detections have been made, the absence of signals itself informs theoretical models. As observational capabilities advance, GRB afterglows will remain a powerful tool for unveiling the invisible majority of our universe’s matter.