1. The NANOGrav 15 yr data set: evidence for a gravitational-wave background;Agazie;Astrophys. J. Lett.,2023
2. The second data release from the European pulsar timing array - III. Search for gravitational wave signals;Antoniadis;Astron. Astrophys.,2023
3. Search for an isotropic gravitational-wave background with the parkes pulsar timing array;Reardon;Astrophys. J. Lett.,2023
4. Black holes in the early universe;Carr;Mon. Not. R. Astron. Soc.,1974