{"work":{"id":"ecdcd896-0d01-4707-9631-446c2f7bb47b","openalex_id":null,"doi":null,"arxiv_id":"2306.16213","raw_key":null,"title":"The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background","authors":null,"authors_text":"Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Bence Becsy","year":2023,"venue":"astro-ph.HE","abstract":"We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15-year pulsar-timing data set collected by the North American Nanohertz Observatory for Gravitational Waves. The correlations follow the Hellings-Downs pattern expected for a stochastic gravitational-wave background. The presence of such a gravitational-wave background with a power-law-spectrum is favored over a model with only independent pulsar noises with a Bayes factor in excess of $10^{14}$, and this same model is favored over an uncorrelated common power-law-spectrum model with Bayes factors of 200-1000, depending on spectral modeling choices. We have built a statistical background distribution for these latter Bayes factors using a method that removes inter-pulsar correlations from our data set, finding $p = 10^{-3}$ (approx. $3\\sigma$) for the observed Bayes factors in the null no-correlation scenario. A frequentist test statistic built directly as a weighted sum of inter-pulsar correlations yields $p = 5 \\times 10^{-5} - 1.9 \\times 10^{-4}$ (approx. $3.5 - 4\\sigma$). Assuming a fiducial $f^{-2/3}$ characteristic-strain spectrum, as appropriate for an ensemble of binary supermassive black-hole inspirals, the strain amplitude is $2.4^{+0.7}_{-0.6} \\times 10^{-15}$ (median + 90% credible interval) at a reference frequency of 1/(1 yr). The inferred gravitational-wave background amplitude and spectrum are consistent with astrophysical expectations for a signal from a population of supermassive black-hole binaries, although more exotic cosmological and astrophysical sources cannot be excluded. The observation of Hellings-Downs correlations points to the gravitational-wave origin of this signal.","external_url":"https://arxiv.org/abs/2306.16213","cited_by_count":null,"metadata_source":"pith","metadata_fetched_at":"2026-05-19T16:07:40.503761+00:00","pith_arxiv_id":"2306.16213","created_at":"2026-05-09T05:50:27.445269+00:00","updated_at":"2026-05-19T16:07:40.503761+00:00","title_quality_ok":true,"display_title":"The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background","render_title":"The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background"},"hub":{"state":{"work_id":"ecdcd896-0d01-4707-9631-446c2f7bb47b","tier":"hub","tier_reason":"10+ Pith inbound or 1,000+ external citations","pith_inbound_count":52,"external_cited_by_count":null,"distinct_field_count":7,"first_pith_cited_at":"2025-04-02T12:17:19+00:00","last_pith_cited_at":"2026-05-14T18:00:00+00:00","author_build_status":"not_needed","summary_status":"needed","contexts_status":"needed","graph_status":"needed","ask_index_status":"not_needed","reader_status":"not_needed","recognition_status":"not_needed","updated_at":"2026-05-19T18:21:31.499686+00:00","tier_text":"hub"},"tier":"hub","role_counts":[{"context_role":"background","n":22},{"context_role":"dataset","n":3},{"context_role":"extension","n":1},{"context_role":"method","n":1}],"polarity_counts":[{"context_polarity":"background","n":20},{"context_polarity":"use_dataset","n":3},{"context_polarity":"extend","n":1},{"context_polarity":"support","n":1},{"context_polarity":"unclear","n":1},{"context_polarity":"use_method","n":1}],"runs":{},"summary":{},"graph":{},"authors":[]}}