Research with LOFAR is organized into a number of ‘Key Science Projects’ (KSPs) that address particular scientific themes. The LOFAR KSPs are independently organized international research groups which are required to make recognized contributions to the development of LOFAR and its scientific output. Astrophysics groups in Ireland are also part of these international KSPs, a selection of which are listed below.
Following the Big Bang, a period of the Universe’s history probed extensively over the past couple of decades by cosmic microwave background experiments, sub-atomic particles combined together to form neutral hydrogen. The first stars in the early universe formed from this neutral environment. Once these stars ignited, they flooded the Universe with light, leading to the ionization of this surrounding neutral environment. This is known as the Epoch of Reionization (EoR, see image below), leading the Universe out of its ‘dark-ages’ and to the birth of the first stars to come into existence. Exactly when and how this reionization occurred is one of the great unanswered questions in modern cosmology and studying the EoR has been one of the key drivers for the design of LOFAR, the measurements from which could have fundamental implications for astrophysics and theories of the Universe’s formation.
2. All-sky Surveys
The sensitivity and extremely large field-of-view of LOFAR make it an ideal instrument for undertaking deep, large area surveys. LOFAR will produce a series of unique surveys of the low-frequency radio sky, which will open a new window on numerous fundamental areas of astrophysics. Notable amongst these are:
- Formation of massive galaxies, clusters and black holes using z ≥ 6 radio galaxies as probes
- Intercluster magnetic ﬁelds using diffuse radio emission in galaxy clusters as probes
- Star formation processes in the early Universe using starburst galaxies as probes
The Surveys KSP will be optimized for obtaining large samples of radio objects in these and other categories, such as the objects in the LOFAR image below. These objects will be studied individually and also collectively for precision statistical analysis. A number of all-sky, multi-frequency surveys are planned over multiple epochs, also enabling variable sources to be recognized.
3. Transients Sources
Our universe can be a violent and rapidly changing place. Exploding stellar giants, accreting supermassive black holes, rapidly rotating superdense neutron stars, can all release enormous energies into their surrounding environments on very short timescales, acting as cosmic thermostats, keeping the environment in an active state, triggering star formation and regulating the growth of galaxies. In nearly all cases, such events and phenomena have associated radio emission, so by observing in the radio band we can understand where and how often such events occur, and gauge their combined impact on the ambient environment. The LOFAR Transients KSP focuses on exploring and understanding the explosive and dynamic universe by observing transient and variable radio sources. Thanks to the enormous field of view and multiple beams of LOFAR, for the first time we are able to monitor a large fraction of the sky on a regular basis, allowing us to make an accurate census of such sources.
4. Solar Science and Space Weather
The Sun is a powerful emitter at radio wavelengths, not only during intense bursts of activity related to phenomena such as solar flares and coronal mass ejections (CMEs), but also during times when it is considered quiet at other wavelengths. Radio emission from energetic and dynamic phenomena such as solar flares and CMEs is of particular interest, as they are major drivers of space weather and can affect the Earth’s space environment. Solar flares and CMEs are also challenging physical phenomena to be understood in their own right. LOFAR opens an unexplored window of the radio spectrum, which is particularly useful for studying particle acceleration and large-scale dynamics. It will enable the study of accelerated particles, from very weak to very energetic events, especially when combined with multi-wavelength observations from other terrestrial and space-based observatories. An example of such a study is presented in the image below where an ultraviolet image of the Sun is overlaid with a radio burst observed by LOFAR, produced by energetic electrons travelling at a third of the speed of light. With LOFAR, dynamic processes involved in solar flares and CMEs can be studied from their origins on the Sun as they propagate out through the solar atmosphere. Using radio interplanetary scintillation measurements, CMEs can be tracked, and the solar wind and interplanetary magnetic field conditions analysed, from the outer solar corona to the Earth and other planets. Furthermore, radio observations with LOFAR will provide powerful diagnostics of the Earth’s ionosphere and magnetically-linked regions of its magnetosphere.
5. Cosmic Magnetism
Although we know that magnetic fields fill interstellar and intracluster space, their presence on both small and large scales is an often over-looked topic in astrophysics. The full Stokes polarization response and low frequency coverage of LOFAR make it uniquely suited for changing this situation and investigating the magnetic cosmic web in detail. The presence of magnetic fields in astrophysical objects is mainly inferred in one of two ways:
- Firstly, through detecting synchrotron emission, a radiation mechanism which is a direct consequence of magnetic structure
- Secondly, using the rotation of the intrinsic polarization of background sources as their own radiation passes through foreground magnetized media.
Both mechanisms are ideally observed at the low frequencies measured by LOFAR as they are not only intrinsically faint, but their amplitude is also inversely proportional to frequency. The Magnetism KSP will not only examine the Faraday structure of individual objects such as nearby galaxies (see image below), magnetized galaxy cluster haloes, and the interstellar Galactic plane where magnetic fields play vital roles from the onset of star formation to the growth of galaxies; but will also investigate the primordial generation, structure and evolution of magnetic fields on cosmological scales.