- The paper demonstrates that the Uranus Orbiter mission can use Doppler tracking to detect micro-Hz gravitational waves, bridging the gap between pulsar timing arrays and space observatories.
- Numerical models predict the mission will detect between 1 and 100 massive black hole binaries and also potentially stochastic gravitational wave backgrounds in the micro-Hz band.
- The mission's capabilities offer potential to test ultra-light dark matter models, probe early universe phenomena, and significantly complement existing gravitational wave detection efforts.
Bridging the micro-Hz Gravitational Wave Gap
The recent announcement of NASA's Planetary Science and Astrobiology Decadal Survey 2023-2032 has identified the Uranus Orbiter and Probe (UOP) mission as a priority. This paper explores the possibility of utilizing the UOP mission's radio Doppler tracking equipment to detect gravitational waves (GWs) and related signals over the mission's interplanetary cruise. By implementing advanced strategies to stack tracking data and employing Monte-Carlo Markov-Chain parameter recovery tests, the authors demonstrate that the mission will achieve sensitivity to GWs across a frequency range of 3x10-9 Hz to 10-1 Hz, potentially filling the observational gap between pulsar timing arrays (PTAs) and space-based interferometric GW observatories.
The paper predicts the detection of between 1 and 100 individual massive black hole binaries using two independent population models, underscoring the practical viability of Doppler tracking for GW observations. Additionally, the paper addresses the mission's probability of detecting both astrophysical and primordial stochastic gravitational wave backgrounds, along with the potential to test and possibly confirm ultra-light dark matter (ULDM) models. Given these capabilities, the UOP mission is projected to probe unexplored parameters where new cosmic phenomena may reside, thus providing an invaluable complement to existing GW detection efforts.
Methodology
A significant contribution of this paper lies in its approach to utilizing the UOP's long interplanetary cruise for scientific purposes beyond planetary exploration. The paper describes a strategy to stack individual Doppler tracking data segments, analogous to the methodologies used in PTAs for nano-Hz GW detection. This approach sets the lower boundary of the mission's frequency sensitivity achievable through extended observation times. Notably, the researchers forecast sensitivity in the frequency domain between 3x10-9 Hz and 10-1 Hz. This encompasses micro-Hz GWs, which hold immense potential for astrophysical and cosmological studies.
Numerical Results and Models
The model forecasts significant detection capabilities. For instance, the mission is set to detect up to O(1-100) massive black hole binaries using two independent population models. The model allows the exploration of unexplored regions that may contain signals pointing to phenomena such as ULDM. The number of detectable individual binaries largely depends on improvements in tracking technology, which the authors detail across baseline, priority, and optimistic scenarios.
The research highlights that, even using current Doppler tracking technology similar to Cassini-era apparatus, there is potential for detecting stochastic GW backgrounds in the micro-Hz band, especially with enhancements scheduled for the UOP mission. The deployment of multiple tracking stations and improvements in signal stability could substantially refine analytical outcomes, offering a pathway for achieving Allan deviation improvements down to approximately 10-15. The paper explores these scenarios and elucidates their implications.
Implications and Future Directions
The practical implications of these findings include the potential detection of SMBH binaries across a wide array of redshifts, thereby advancing our understanding of black hole formation and growth. Moreover, the possible detection of cosmological GWs from early universe phenomena, such as phase transitions, represents a significant opportunity to probe conditions present during these formative epochs.
The discussion extends to encompass the detection of ULDM via Doppler tracking. The paper projects a promising future for UOP in constraining possible ULDM models, demonstrating immense potential for direct dark matter detection within our solar system, a field uncharted by existing methodologies.
The researchers argue for the integration of these scientific imperatives into the mission's requirements, notably advocating for sustained tracking data acquisition during the interplanetary cruise and technological improvements in Doppler tracking precision. This focus can elevate the UOP mission as a pivotal agent in unveiling critical astrophysical and cosmological insights, thereby bridging key observational gaps in our universe's gravitational wave landscape.