High-Energy Astrophysics
(Hardcastle)
Traditionally, high energy astronomy refers to the study of astronomical objects that release electromagnetic radiation of highly energetic photons (quanta of light). As such, it includes observations in the extreme ultra-violet (UV), X-rays, and gamma-rays. However, with time its extent has broadened to include other high-energy particles that can reach us from astronomical objects, such as neutrinos (weakly interacting nearly massless particles) and cosmic rays (mainly protons or heavier nuclei travelling very close to the speed of light). The physical study of astrophysical phenomena that involve such high-energy particles is referred to as high-energy astrophysics. Astronomical objects commonly studied in this field include black holes, neutron stars, active galactic nuclei, supernova remnants, Gamma ray bursts, and quasars. These objects often release large amounts of energy within a small volume over a short period of time.
These phenomena are of great importance, since they probe extreme physical conditions which are very hard to reproduce in terrestrial laboratories, such as:
- strong gravitational fields
- very high and low densities
- unusually high temperatures
- vast spatial scales and masses
- extremely large magnetic fields
- relativistic bulk motions (coherent ordered motions of large amounts of matter at velocities close to the speed of light)
- individual particles of extremely high energies
They can therefore improve our understanding of basic physics and help address topics that are both fundamental and poorly understood, such as the launching of relativistic jets from accretion of matter onto a compact object (such as a black hole or neutron star), the physics of relativistic collisionless shocks, and how particle acceleration (individual particles acquiring large energies) occurs in nature. These physical processes, as well as others, are common to many of the objects studied in high energy astrophysics.
The high energy astrophysics research at the University of Hertfordshire includes both the study of the physics of these energetic objects, and their uses as probes for other fields of research in astronomy. The latter involves mainly observational work, while the former combines observations, phenomenology, and theory. The theoretical work involves both analytic studies and numerical simulations that require powerful computer facilities. Observationally, satellites that operate at X-ray and gamma-ray energies, such as the X-ray observatories Chandra and XMM-Newton, are a key element of our work. However, since the radiation emitted by high-energy particles often spans the entire observable electromagnetic spectrum, we also use facilities ranging from ground-based low-frequency radio telescopes (the NRAO VLA, the GMRT, and LOFAR), through to the mid-infrared (Spitzer) and the optical and UV (the Hubble Space Telescope and numerous ground-based telescopes).
The main topics that we study are: