Suvi Gezari

The Lazuli Space Observatory is a 3 m aperture astronomical facility designed for rapid-response observations and precision astrophysics across visible to near-IR wavelengths (400–1700 nm bandpass). An off-axis, freeform telescope delivers diffraction-limited image quality (Strehl >0.8 at 633 nm) to three instruments across a wide, flat focal plane. The three instruments provide complementary capabilities; the Wide-field Context Camera (WCC) delivers multiband imaging over a 35 ′ × 12 ′ footprint with high-cadence photometry; the Integral-field Spectrograph (IFS) provides continuous 400–1700 nm spectroscopy at R ∼ 100–500 for stable spectrophotometry; and the ExtraSolar Coronagraph (ESC) enables high-contrast imaging expected to reach raw contrasts of 10 ⁻⁸ and postprocessed contrasts approaching 10 ⁻⁹ . Operating from a 3:1 lunar-resonant orbit, Lazuli will respond to targets of opportunity in under four hours—a programmatic requirement designed to enable routine temporal responsiveness that is unprecedented for a space telescope of this size. Lazuli’s technical capabilities are shaped around three broad science areas: (1) time-domain and multimessenger astronomy, (2) stars and planets, and (3) cosmology. These capabilities enable a potent mix of science spanning gravitational-wave counterpart characterization, fast-evolving transients, Type Ia supernova cosmology, high-contrast exoplanet imaging, and spectroscopy of exoplanet atmospheres. While these areas guide the observatory design, Lazuli is conceived as a general-purpose facility with open time for the global community. We describe the observatory architecture and capabilities in the preliminary design phase, with science operations anticipated following a rapid development cycle from concept to launch; quoted performance specifications reflect current design requirements and modeling predictions, pending on-orbit verification.

Advancing time-domain and multi-messenger astronomy requires a multi-wavelength network of observatories capable of rapidly discovering, classifying, and characterizing transient phenomena. A critical gap in current capabilities is the inability to follow up faint, fast-evolving transients with sensitive, wide-band imaging and spectroscopic observations from space on timescales of minutes to hours. We discuss how the Lazuli Space Observatory will address this gap through a large collecting area, optical/NIR photometry and low-resolution integral field spectroscopy, and a rapid-response architecture with a mission requirement of <4 hr from trigger to first photon. Based on a latency analysis, we find a credible path to realizing response times well below this requirement, with best-case scenarios below 90 minutes under favorable conditions. We highlight extragalactic science opportunities in currently un(der)explored parts of parameter space, including gravitational wave follow-up, kilonova characterization, supernova progenitor physics, and a wide variety of fast-evolving transients and high redshift events. We further outline new observational capabilities for Galactic time-domain science, including high frequency variability in accreting systems, precision astrometry of compact objects, and the detection of compact and ultracompact binaries, enabled by high-frequency, diffraction-limited imaging and astrometry. Together, its capabilities—combining flagship sensitivity with response times one to two orders of magnitude faster than existing large space observatories—position Lazuli to make transformative contributions across time-domain and multi-messenger astrophysics.

Tidal disruption events (TDEs) have traditionally been discovered in optical sky surveys through targeted searches of nuclear transients. However, it is expected that some TDEs will occur outside the galaxy nucleus, arising from wandering black holes (BHs) originating in galaxy mergers. Here, we present observations of TDE 2025abcr, the first optical TDE discovered in the outskirts of a host galaxy. The TDE was identified by a custom “off-nuclear” implementation of the machine learning classifier tdescore , which classifies new ZTF transients based on their lightcurves. Follow-up observations confirm that TDE 2025abcr is a TDE-H+He, occurring 9 . ″ 5 (9.3 kpc projected distance) from the nucleus of a massive galaxy ( M _⋆ = 10 ^11.18±0.03 M _⊙ ) with a central BH mass of 10 ^8.82±0.65 M _⊙ . TDE 2025abcr itself was likely disrupted by a much lighter BH (10 ^6.09±0.53 M _⊙ , as estimated with peak luminosity scaling relations). The BH was either dynamically ejected from the nucleus or lies at the center of a very faint tidally stripped dwarf galaxy undergoing a minor merger. Late-time observations of TDE 2025abcr could confirm the origin of this apparent “wandering” BH. The rate of highly offset (≳3 kpc) TDEs can be constrained to <10% of the nuclear TDE rate, but our discovery implies that many dozens of similar sources will be detected by the Vera C. Rubin Observatory each year with resolvable offsets.

Measuring the mass distribution of supermassive black holes (SMBHs) over cosmic time remains particularly challenging for the low-mass ( M _• ≲ 10 ⁸ M _⊙ ) population at z > 1. This population is also the most sensitive to SMBH seeding and early growth models. In this work, we construct a semiempirical model for the redshift evolution of the tidal disruption event (TDE) rate under multiple SMBH mass function prescriptions, and show that the observed redshift-dependent rate of TDEs is very sensitive to the SMBH mass function and its evolution with redshift. We further incorporate galaxy-scale processes that evolve with redshift—namely, increasing galaxy nuclear stellar densities, enhanced galaxy–galaxy merger rates, dust obscuration, and a possible top-heavy initial mass function at early cosmic times—and quantify their combined impact on the TDE rate. We find that including these effects generally results in a volumetric TDE rate that increases with redshift until a maximum near cosmic noon, before declining at higher redshift, where SMBHs that can disrupt stars become increasingly scarce. We forecast TDE rates in the Rubin Legacy Survey of Space and Time (LSST) and the Roman High Latitude Time Domain Survey, alongside expectations for serendipitous TDE rates in the JWST COSMOS-Web survey. Finally, we provide a methodology for using a flux-limited survey of TDEs in LSST to directly constrain the redshift evolution of the SMBH mass function.

We present an analysis of the spectral energy distribution (SED) of the off-nuclear tidal disruption event (TDE) AT2024tvd during its late-time plateau phase, combining X-ray spectra and UV/optical photometry. Using a fully relativistic, compact accretion disk model with self-consistent inner-disk Comptonization, we reproduce the observed SED without significant residuals. The inferred black hole mass log 10 ( M • / M ⊙ ) ≈ 6.0 ± 0.2 , and the inferred disk parameters place AT2024tvd within known TDE-disk scaling relations ( L bol disk / L Edd ∝ T p 4 ∝ M • − 1 , L plat ∝ M • 2 / 3 , R out / r g ∝ M • − 2 / 3 ). Our results show that: (i) there is no currently detected star cluster or dwarf galaxy associated with the source, down to a mass limit of log 10 ( M gal / M ⊙ ) ≤ 7.6 ; (ii) the black hole is a wandering supermassive, rather than intermediate-mass, black hole; and (iii) the source represents an extreme case of black hole-to-host mass ratio, with M _• / M _gal > 3%, consistent with a heavily tidally stripped nucleus. The latter aligns with cosmological simulations predicting that surviving host remnants of most wandering black holes should not retain a detectable stellar overdensity when located at small halo-centric distances. We discuss differences with previous analyses of this source and highlight why our modeling approach provides a more physically consistent solution with more reliable parameter inference.

Transient astronomy of the early, high-redshift ( z > 3) Universe is an unexplored regime that offers the possibility of probing the first stars and the epoch of reionization. During Cycles 1 and 2 of the James Webb Space Telescope (JWST), the JWST Advanced Deep Extragalactic Survey program enabled one of the first searches for transients in deep images (∼30 AB mag) over a relatively wide area (25 arcmin ² ). One transient, AT 2023adsv, was discovered with an F200W magnitude of 28.04 AB mag, and subsequent JWST observations revealed that the transient is a likely supernova (SN) in a host with z _spec = 3.613 ± 0.001 and an inferred metallicity at the position of the SN of Z _* = 0.3 ± 0.1 Z _⊙ . At this redshift, the first detections in F115W and F150W show that AT 2023adsv had bright rest-frame UV flux at the time of discovery. The multiband light curve of AT 2023adsv is best matched by a template of a Type IIP SN (SN IIP) with a peak absolute magnitude of M _B ≈ −18.3 AB mag. We find a good match to a 20 M _⊙ red supergiant progenitor star with an explosion energy of 2 × 10 ⁵¹ erg, likely higher than normally observed in the local Universe, but consistent with SNe IIP drawn from local, lower-metallicity environments. AT 2023adsv is the most distant photometrically classified SN IIP yet discovered with a spectroscopic redshift measurement, and may represent a global shift in SN IIP properties as a function of redshift.

Multiwavelength analyses of astrophysical transients are essential for understanding the physics of these events. To make such analyses more efficient and effective, we present the Open mulTiwavelength Transient Event Repository (OTTER), a publicly available catalog of published transient event metadata and photometry. Unlike previous efforts, our data schema is optimized for the storage of multiwavelength photometric datasets spanning the entire electromagnetic spectrum from multiple published sources. Open-source software, including an application programming interface (API) and web application, are available for viewing, accessing, and analyzing the dataset. For the initial release of OTTER, we present the largest ever photometric archive of tidal disruption event (TDE) candidates, including ≳118,000 observations of 240 TDE candidates spanning from radio to X-ray wavelengths. We demonstrate the power of this infrastructure through four example analyses of the TDE population. We plan to maintain this dataset as more TDE candidates are proposed in the future and encourage other users to contribute by uploading newly published data via our web application. The infrastructure was built with the goal of archiving additional transient data (supernovae, gamma-ray bursts, fast blue optical transients, fast radio bursts, etc.) in the future. The web application is available at https://otter.idies.jhu.edu and the API documentation is available at https://astro-otter.readthedocs.io .

Here we summarize discussions and conclusions from the conference “The Era of Binary Supermassive Black Holes: Coordination of Nanohertz-Frequency Gravitational-Wave Follow-up,” held at the Aspen Center for Physics from February 2-7, 2025. The meeting facilitated a crucial knowledge exchange between electromagnetic and gravitational-wave theorists, observers, and cyber-infrastructure experts. The central goal was to guide the development of multi-messenger follow-up strategies for binary supermassive black hole detections by pulsar timing arrays. To build a common basis of understanding for the broader scientific community, this summary outlines the main considerations and recommendations from the meeting, summarizes the knowledge gaps identified, and ends with a potential roadmap to catalyze discussion about the search for electromagnetic counterparts to massive black hole binaries detected by pulsar timing arrays.