Zhen-Zhao Tao

Building on prior FAST targeted and blind SETI campaigns toward 33 exoplanet systems, we introduce a wavelet-integrated search pipeline for narrowband technosignature candidates in dynamic radio spectra. At its core, the pipeline uses a Multiscale Wavelet Net to produce an interpretable multiresolution representation, followed by a lightweight parameter estimator for endpoint localization. Rather than relying solely on hard-threshold drift searches, the pipeline reframes narrowband detection as wavelet-guided feature extraction followed by endpoint regression, morphology-aware filtering, raw-data signal-to-noise ratio validation, and multibeam anticoincidence veto. Applied to real FAST data, the pipeline recovers representative events from prior analyses and produces a compact set of veto-ready candidates for downstream inspection. The resulting workflow preserves interpretability, low-regression complexity, and auditable threshold control, making it readily transferable to other radio surveys and large-scale technosignature searches.

The Five-hundred-meter Aperture Spherical Telescope (FAST) is the world’s largest single-dish radio telescope, and the search for extraterrestrial intelligence (SETI) is one of its five key science objectives. We conducted a targeted search for unresolved narrowband radio technosignatures toward the TRAPPIST-1 system using FAST. The observations consisted of five independent L -band pointings, each with a 20 minute integration, for a total on-source time of 1.67 hr. The frequency coverage spanned 1.05–1.45 GHz with a spectral resolution of ∼7.5 Hz. We searched Stokes I (total intensity) data for drifting signals with Doppler drift rates within ±20 Hz s ⁻¹ and a signal-to-noise ratio threshold of S/N = 10. For unresolved, minimally drifting narrowband signals, the nominal minimum detectable equivalent isotropic radiated power is EIRP min ≈ 1.44 × 1 0 10 W . We explicitly quantify how this limit degrades at high drift rates because of tree de-Doppler power smearing, reaching ≈3.84 × 10 ¹¹ W at ∣ ν ̇ ∣ = 20 Hz s − 1 under a conservative peak-channel sensitivity correction. No credible technosignature candidates attributable to the TRAPPIST-1 system were identified within the searched parameter space. Nevertheless, TRAPPIST-1 remains a compelling target for future SETI efforts. We plan to extend our search to other signal types, such as periodic, transient, broadband, and propagation-broadened transmitters, and to carry out broader surveys of nearby exoplanetary systems with FAST.

We develop a model-independent framework to quantify phase-space “crystallization,” the degree of ordered radial and kinematic substructure, in 79 Galactic globular clusters using the Gaia EDR3–based membership catalog of E. Vasiliev & H. Baumgardt. We construct a scalar crystallization index, C _index , by combining a radial inhomogeneity metric ( z _rad ) and a local, cluster-centric tangential-velocity metric ( z _vel ) standardized against empirical nulls. The population distribution is strongly non-Gaussian: most clusters are consistent with smooth, equilibrium expectations, while a small high- C tail ( C _index ≥ 2) identifies dynamically complex systems, including NGC 5139 ( ω Cen) and NGC 104 (47 Tuc). Correlation and fixed- N tests show that sample size affects detectability, but does not by itself explain all high-rank objects. Through synthetic injection tests in dynamically “quiet” control clusters, we demonstrate sensitivity to ultra-cold, shell-confined kinematic components, ruling out single-shell structures comprising more than a few to ∼10%–20% of core stars in the best-sampled control clusters. We find no evidence, within the sensitivity of the adopted diagnostics, for phase-space structures that require explanations beyond known dynamical processes. However, C _index provides a useful tool for ranking clusters by dynamical extremeness, serving both as a diagnostic for internal complexity and as a quantitative metric for prioritizing follow-up dynamical or technosignature-oriented observations.

We search for galaxy-scale (Dysonian) waste heat in the mid-infrared using WISE. Starting from the 2MASS Redshift Survey, we crossmatch to CatWISE2020 and AllWISE, apply standard MIR AGN/starburst vetoes (Stern, Assef R90, Jarrett), and treat W1 and W2 as stellar baselines and W3 and W4 as constraining bands. For each galaxy and for blackbody waste heat temperatures T = 150–600 K, we convert W3/W4 photometry into conservative 3 σ per-galaxy upper limits on the bolometric waste heat luminosity using the WISE bandpass color correction. The resulting distributions have median caps of ∼(5–9) × 10 ⁸ L _⊙ across T = 150–600 K. Aggregated at the population level, the one-sided 95% upper bound on the fraction of nearby galaxies that could host waste heat above a given threshold monotonically decreases with threshold and asymptotes to ≃1/6500 at high thresholds (set by the sample size). Sensitivity transitions from W4 at T ≲ 200 K to W3 at T ≳ 300 K. Interpreted with the AGENT formalism, a fiducial Milky Way like stellar luminosity L _⋆ = 3 × 10 ¹⁰ L _⊙ implies typical per galaxy caps of α ≡ L _wh / L _⋆ ≲ 1.7%–2.9% over T = 150–600 K (e.g., α ≲ 1.8% at T = 300 K). At T ≃ 300 K, no more than f ₉₅ ≃ 1.61 × 10 ⁻⁴ ( ≃0.0161%) of nearby galaxies can host KIII-scale systems reprocessing ≳21% of a Milky-Way-like stellar luminosity into ∼300 K waste heat.

We report a radio SETI search for periodic, kHz-wide signals from five of the nearest stars observable with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Using the 19-beam L-band receiver (1.05-1.45 GHz), we obtained 1200 s tracking observations of Groombridge 34 A/B, Ross 248, 61 Cygni B, and Ross 128. Dynamic spectra from all beams and both linear polarisations were searched channel by channel with a fast-folding algorithm sensitive to periods between 1.1 and 300 s. A multi-layer RFI-mitigation pipeline exploits multi-beam occupancy, cross-target bad-channel statistics, XX/YY polarisation coincidence, broad frequency masks, and narrow site-specific RFI exclusion zones, followed by clustering in period-frequency space. The pipeline is validated on FAST observations of PSR B0329+54, where we recover the known 0.714 s spin period and harmonic structure in the expected beam. For the stellar sample, successive cuts reduce the raw FFA hit lists (> 10^6 hits per target) to a small number of cluster-level candidates, all of which exhibit clear radio-frequency interference signatures in phase-time and phase-frequency diagnostics. We therefore report no convincing detections of periodic transmitters in our searched parameter space. Using the radiometer equation with our adopted detection threshold (S/N = 25) and assuming a duty cycle delta = 0.1, we obtain upper limits of approximately (7-9) x 10^9 W on the isotropic-equivalent EIRP of kHz-wide periodic beacons at these stars, among the most stringent constraints to date on periodic radio emission from nearby stellar systems.

The search for extraterrestrial intelligence (SETI) commensal surveys aim to scan the sky to detect technosignatures from extraterrestrial life. A major challenge in SETI is the effective mitigation of radio frequency interference (RFI), a critical step that is particularly vital for the highly sensitive Five-hundred-meter Aperture Spherical radio Telescope (FAST). While initial RFI mitigation (e.g., removal of persistent and drifting narrowband RFI) are essential, residual RFI often persists, posing significant challenges due to its complex and various nature. In this paper, we propose and apply an improved machine learning approach, the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm, to identify and mitigate residual RFI in FAST–SETI commensal survey archival data from 2019 July. After initial RFI mitigation, we successfully identify and remove 36,977 residual RFIs (accounting for ∼77.87%) within approximately 1.678 s using the DBSCAN algorithm. This result shows that we have achieved a 7.44% higher removal rate than previous machine learning methods, along with a 24.85% reduction in execution time. We finally find interesting candidate signals consistent with previous studies, and retain one candidate signal following further analysis. Therefore, DBSCAN algorithm can mitigate more residual RFI with higher computational efficiency while preserving the candidate signals that we are interested in.

The Five-hundred-meter Aperture Spherical Telescope (FAST), the world’s largest single-dish radio telescope, lists the search for extraterrestrial intelligence (SETI) as one of its key scientific objectives. In this work, we present a targeted SETI observation for seven nearby active stars utilizing the FAST L-band multibeam receiver, employing an observational strategy that combines position switching with multibeam tracking to balance on-source integration time with the accuracy of the beam response. Using both pulsar and SETI backends, we perform a comprehensive search for narrowband drifting signals with Doppler drift rates within diversified ranges and channel-width periodic signals with periods between 0.12 and 100 s and duty cycles between 10% and 50%. No credible radio technosignatures were detected from any of the target systems. Based on this null result, we place constraints on the presence of transmitters at a 95% confidence level, ruling out narrowband transmitters with EIRP above 3.98 × 10 ⁸ W and periodic transmitters with EIRP above 1.80 × 10 ¹⁰ W within the observation band.

Gravitational waves (GWs) can convert into electromagnetic waves in the presence of a magnetic field via the Gertsenshtein–Zeldovich effect. The characteristics of the magnetic field substantially affect this conversion probability. This paper confirms that strong magnetic fields in neutron stars significantly enhance the conversion probability, facilitating detectable radio signatures of very high-frequency (VHF, 1 0 6 – 1 0 11 Hz ) GWs. We theoretically identify two distinct signatures using single-dish telescopes (FAST, TMRT, QTT, GBT) and interferometers (SKA1/2-MID): transient signals from burst-like GW sources and persistent signals from cosmological background GW sources. These signatures are mapped to graviton spectral lines derived from quantum field theory by incorporating spin-2 and mass constraints, resulting in smooth, featureless profiles that are critical for distinguishing GW signals from astrophysical foregrounds. FAST attains a characteristic strain bound of h _c < 10⁻²³, approaching 10⁻²⁴ in the frequency range of 1–3 GHz with a 6 hr observation period. This performance exceeds the 5σ detection thresholds for GWs originating from primordial black holes and nears the limits set by Big Bang nucleosynthesis. Additionally, projections for SKA2-MID indicate even greater sensitivity. Detecting such GWs would improve our comprehension of cosmological models, refine the parameter spaces for primordial black holes, and function as a test for quantum field theory. This approach addresses significant deficiencies in VHF GW research, improving detection sensitivity and facilitating the advancement of next-generation radio telescopes such as FASTA and Square Kilometre Array, which feature larger fields of view and enhanced gain.

The search for extraterrestrial intelligence (SETI) targeted searches aim to observe specific areas and objects to find possible technosignatures. Many SETI researches have focused on nearby stars and their planets in recent years. In this paper, we report a targeted SETI observations using the most sensitive L-band Five-hundred-meter Aperture Spherical radio Telescope toward three nearby M dwarfs, all of which have been discovered exoplanet candidates. The minimum equivalent isotropic radiant power of the lower limit from the three sources we can detect is 6.19 × 10⁸ W, which is well within the reach of current human technology. Applying the multibeam coincidence matching blind search mode, we search for narrowband drifting signals across 1.05–1.45 GHz in each of the two orthogonal linear polarization directions. An unusual signal at 1312.50 MHz detected from the observation toward AD Leo originally piqued our interest. However, we finally eliminate the possibility of an extraterrestrial origin based on much evidence, such as the polarization, frequency, and beam coverage characteristics.

We present an independent validation and comprehensive recalibration of S-PLUS Ultra-short Survey (USS) DR1 12-band photometry using about 30,000–70,000 standard stars from the Best Star (BEST) database. We identify the spatial variation of zero-point offsets, up to 30–40 mmag for blue filters (u, J0378, and J0395) and 10 mmag for others, predominantly due to the higher uncertainties of the technique employed in the original USS calibration. Moreover, we detect large- and medium-scale CCD position-dependent systematic errors, up to 50 mmag, primarily caused by different aperture and flat-field corrections. We then recalibrate the USS DR1 photometry by correcting the systematic shifts for each tile using second-order two-dimensional polynomial fitting combined with a numerical stellar flat-field correction method. The recalibrated results from the XP spectrum based synthetic photometry and the stellar color regression standards are consistent within 6 mmag in the USS zero-points, demonstrating both the typical precision of the recalibrated USS photometry and a sixfold improvement in USS zero-point precision. Further validation using the Sloan Digital Sky Survey and Pan-STARRS1, as well as LAMOST DR10 and Gaia photometry, also confirms this precision for the recalibrated USS photometry. Our results clearly demonstrate the capability and efficiency of the BEST database in improving calibration precision to the millimagnitude level for wide-field photometric surveys. The recalibrated USS DR1 photometry is publicly available on ChinaVO at doi:10.12149/101503.