“They missed it because they hadn’t expected to find anything like it.” 2023 July 19, NatureRead More
Pulsars and Fast Transients
The Pulsar and Fast Transient (PFT) science working group is primarily interested in the wide range of science streams enabled by the Voltage Capture System (VCS). This includes (but is not limited to): pulsars, fast radio bursts (FRBs), passive radar, cosmic ray detection, some areas of solar science, and atmospheric phenomena such as lightning that require high-time or frequency resolution data.
The VCS allows exploration of a frequency range in which the vast majority of pulsars have very little or no published information. Some major themes are:
- The pulsar emission mechanism, i.e. studying phenomena such as giant pulses, sub-pulse drifting, and emission intermittency
- Survey and monitoring science, i.e characterising known pulsars, detection of new pulsars, and regular monitoring of targets of interest, and
- Propagation effects induced by the interstellar medium, i.e pulse broadening/scattering, scintillation and dispersion measure variations (in time and frequency).
Ever since their discovery more than 50 years ago, pulsars – fast-spinning, highly-magnetised, tiny, yet very dense stars – have continued to amaze astronomers. They are arguably amongst the most widely-exploited astrophysical objects. They are the sites of extreme environments, with physical conditions such as ultra-strong gravitational and magnetic fields; their exceptional clock-like rotational stability can be exploited for a wide variety of applications in physics and astrophysics. It is no surprise that science centred around pulsars is also a key science for the Square Kilometre Array (SKA) project.
Among the headline science themes within “pulsars and gravity” is the applications of pulsars for performing exquisite tests of Einstein’s theory of gravity or general relativity. This involves the use of specialised systems comprising neutron-star pairs, or pairs of a neutron star with another star, in close binary orbit. Another high-profile application of pulsars is using very fast-spinning ones known as “millisecond pulsars” (i.e. with spin periods of the order of a few milliseconds) to detect gravitational waves at very low frequencies – in the nanohertz range. These are among the high-priority science objectives for the SKA.
The importance of the latter is particularly reinforced by the detection of gravitational-waves by ground-based detectors such as the Laser Interferometer Gravitational-wave Observatory that are most sensitive to the kHz – Hz frequency range. These are produced by mergers of black holes that are ~50-100 times more massive than our Sun. To detect gravitational waves produced by even more massive black holes – those that are millions to billions of times more massive than the Sun, we need to synthesise a galactic-scale detector, which can be done only using a celestial distribution of millisecond pulsars, known as pulsar timing arrays (PTAs). The success on this front will be the next major milestone in gravitational-wave astronomy, and it will extend the new window for astronomy to the nanohertz-frequency range.