Gravitational Wave (GW) astronomers around the world have been very concerned after reading the draft budgets for the next financial year which have been put forward by NASA and the US National Science Foundation (NSF).
The NASA budget request stops funding for LISA, the space based GW observatory currently being planned and designed. It will be formed of three spacecraft each separated by 2.5 million km, but linked by laser beams. As GWs from merging black holes and compact binaries sweep by and distort space, this changes the distance between the spacecraft by a tiny but measurable amount through the technique of ‘interferometry’.
This mission was first proposed to the European Space Agency (ESA) and NASA in the early 1990’s. However, in 2011 NASA pulled out because of funding constraints but ESA continued with its development. NASA re-engaged with ESA in 2017 and agreed to provide expertise and develop certain key components. ESA formally adopted LISA as a mission in 2024, with a major UK contribution, with a planned launch in the mid 2030’s. China has plans to launch the Taiji GW observatory in a similar timeframe to LISA.
Many of you will have heard of LIGO which first detected GW from a merging black hole in September 2015, followed in August 2017 with those from a merging neutron star binary. It did this using the same interferometric techniques which will be used by LISA but using two ground based detectors: one in Washington State and one in Louisiana State, both in the USA. By having two detectors it increases the significance of the detection — if only one detector detected an event it is more likely due to instrumental noise. Perhaps more importantly, having two detectors, which are widely separated on the Earth, it dramatically narrows the region of sky in which the event took place.
Armagh is a partner of both the Gravitational-wave Optical Transient Observer (GOTO) and BlackGEM whose prime goal is to detect the optical counterpart of GW events. If the LIGO detectors can’t reasonably constrain the position events, it is much more difficult to identify an optical counterpart and hence the galaxy, distance and energy of the event. Although there are other GW detectors, (Virgo in Italy, and KAGRA in Japan), they are not as sensitive as the LIGO detectors. Astronomers were looking forward to both LIGO detectors resuming operation on June 11th after some maintenance work which they did successfully; they have planned operation until at least Oct 2025. There is then planned down time until the end of 2027 when both sites are due upgrades.
Astronomers will keenly wait developments in this story until the final budgets are approved or amended by the US Congress.
Gavin Ramsay is the Chair of the UK Research and Innovation (UKRI)/Science and Technology Facilities Council (STFC) Gravitational Wave Grant Panel, but writes here in his personal capacity.