Recorded live 29 June 2023. Gravitational waves play a cosmic symphony as they pass through our galaxy. This week, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) Physics Frontiers Center released the results of 15 years of data in a set of papers published in The Astrophysical Journal Letters. This research is the first evidence of gravitational waves at very low frequencies.   The team, comprised of 190 scientists, transformed our region of the Milky Way Galaxy into an immense gravitational-wave antenna using pulsars. NANOGrav's endeavor involved collecting data from 68 pulsars, fashioning a pulsar timing array—a distinctive type of detector.   In 2020, with over a decade of data, NANOGrav scientists detected hints of an additional enigmatic "hum" in the timing behavior of all the pulsars in their array. After exploring alternative explanations, they grew confident in the authenticity of this signal. Its detection became increasingly feasible with more extensive observations.    However, at that stage, the gravitational-wave signature predicted by general relativity remained too faint to emerge. After fifteen years of pulsar observations, the evidence of gravitational waves, with periods spanning years to decades, emerges prominently.   Join Simon Steel, Deputy Director of the Carl Sagan Center, as he discusses this groundbreaking research with NANOGrav team member and SETI Institute researcher Dr. Michael Lam. Press release: https://www.seti.org/press-release/nanogravs-15-year-journey-reveals-cosmic-hum   We've added a new way to donate to 365 Days of Astronomy to support editing, hosting, and production costs.  Just visit: https://www.patreon.com/365DaysOfAstronomy and donate as much as you can! Share the podcast with your friends and send the Patreon link to them too!  Every bit helps! Thank you! ------------------------------------ Do go visit http://www.redbubble.com/people/CosmoQuestX/shop for cool Astronomy Cast and CosmoQuest t-shirts, coffee mugs and other awesomeness! http://cosmoquest.org/Donate This show is made possible through your donations.  Thank you! (Haven't donated? It's not too late! Just click!) ------------------------------------ The 365 Days of Astronomy Podcast is produced by the Planetary Science Institute. http://www.psi.edu Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org.