Gamma rays: highest energy form of light in the universe.
Emitted by extreme astronomical objects.
Traditional telescope methods (radio, microwave, visible, UV) ineffective for gamma rays.
Challenges of Focusing Gamma Rays
Gamma rays have the shortest wavelength in the electromagnetic spectrum.
Photons of gamma rays pass through typical mirror materials, making focusing impractical.
X-rays are slightly easier to focus, using grazing angle mirrors, but this is also impractical for gamma rays due to the required shallower angles and longer tubes.
Earth's atmosphere absorbs most gamma rays, necessitating space-based telescopes.
Fermi Gamma-Ray Space Telescope
Launched in June 2008.
Detector size: comparable to a small car.
Two main instruments onboard:
Gamma-ray burst detector: designed to find sudden, bright gamma-ray bursts.
Large Area Telescope (LAT):
Similar to particle accelerator detectors.
Made of thin metal sheets.
High-energy gamma rays convert into an electron-positron pair upon impact.
Charged particles create small electric currents as they pass through silicon microstrip detectors.
Paths of particles lead to an endpoint detector that measures total energy, helping establish the source of gamma rays on the sky.
Limitations and Image Resolution
Gamma-ray telescopes cannot focus light, leading to lower resolution images compared to visible or infrared telescopes.
Fermi images are fuzzier, lacking detail seen in visible wavelengths.
Example: Crab Nebula in visible light vs. gamma rays.
LAT has a field of view of 20% of the sky, imaging the entire sky in about three hours.
Resolution: a few arc minutes compared to Hubble's 0.04 arc seconds.
Scientific Discoveries
Gamma rays reveal fascinating cosmic phenomena:
Fermi bubbles around the Milky Way, origins still debated.
All-sky gamma-ray map shows various sources including:
Blazers (supermassive black holes emitting jets of radiation).
Cosmic rays, supernovae, and pulsars.
Afterglow of the neutron star merger in 2017.
Gamma-ray astronomy plays a crucial role in multi-messenger astronomy (combining gravitational waves and electromagnetic detection).
Conclusion
Numerous sources of gamma rays remain mysterious, indicating ongoing scientific exploration in high-energy astrophysics.
Encouragement for questions and further engagement with the topic.