We present volumetric rates and luminosity functions (LFs) of Type Ia supernovae (SNe Ia) from the All-Sky Automated Survey for Supernovae (ASAS-SN), covering the 11-year period from 2014 to 2024. By combining the 2014–2017 V-band sample with the 2018–2024 g-band sample, we construct a large statistical dataset of 1776 SNe Ia. We compute completeness corrections based on injection-recovery simulations of the ASAS-SN light curves, taking into account the variations in light curve shapes. For our standard sample (M_g,peak<-16.0 mag), we extract a total volumetric SN Ia rate of R_tot = (2.55 ± 0.12) × 10^4 yr^-1 Gpc^-3 h_70^3 at a median redshift of z=0.029. With a statistical uncertainty of 4.7%, this is the most precise local measurement to date. While the "normal" SNe Ia account for (92.7 ± 1.9)% of this rate, the total LF reveals immense diversity, with M_g,peak spanning over five magnitudes. The LF of SNe Iax is also broad and rises toward lower luminosities, resulting in a likely lower limit of (4.3 ± 1.8)% of the total rate. We place strong constraints on the rate of SNe Ia-CSM, finding they account for only (0.036 ± 0.017)% of the total local rate. Finally, we find that the low-luminosity 02es-like SNe are 7 ± 5 times more common than the luminous 03fg-like SNe. This places demographic constraints on models proposing a physical continuum for these two subtypes, implying that any common channel for the two classes must strongly favor lower-luminosity explosions.

We present the first data release (DR1) of the Spectroscopic Classification of Astronomical Transients (SCAT) survey, covering the first ≈ 5 years of observations (March 2018 - January 2023). DR1 includes 1812 spectra of 1331 transients, which we sort into broad spectroscopic classes including supernovae (SNe), transients originating in galactic nuclei, and stellar variability. We collect multi-filter light curves from imaging surveys and fit them with phenomenological models to estimate peak brightnesses and the time of explosion/first-light. Extragalactic transients are matched to candidate host galaxies, and we compare host-galaxy luminosities and projected offsets by SN type. SNe appear to be a reliable way to augment the redshift coverage of nearby (z≲ 0.1) galaxies in tandem with dedicated redshift surveys. We present new redshifts for roughly half of the SN host galaxies, most of which are low-luminosity dwarfs similar to the Magellanic Clouds (M_r ≳ -18 mag). This set of transient spectra, light curves, luminosities, redshifts, and host galaxies offers an excellent testbed for real-time photometric/light curve classification pipelines in the modern era of deep and large-area surveys. We conclude with a brief discussion of the provided data products and status of the SCAT survey.

Nuclear transients are powerful probes of supermassive black hole properties, offering insight into black hole mass, accretion physics, and the structure of galactic nuclei. Among these, a growing class of events cannot be classified as either tidal disruption events (TDEs) or active galactic nuclei (AGN) flares, and their physical origins remain poorly understood. We present a multi-wavelength photometric and spectroscopic analysis of AT2021yky (ZTF21abzciqh), an ambiguous nuclear transient (ANT) at a redshift of z = 0.076. AT2021yky reached a peak bolometric luminosity of L_ peak = (4.1 ± 1.1) × 10^43 erg s^-1, with a rise-time of 18.2 ± 0.7 days. The early-time UV/optical emission is well described by a blackbody with a temperature of T ≃ 1.4 × 10^4 K, cooler than most optically selected TDEs. No X-ray emission from the transient is detected, with a 3σ limit of L_X ≲ 3.4 × 10^41 erg s^-1 near peak. Spectroscopic observations reveal a largely featureless blue continuum with broad (FWHM∼ 11,000 km s^-1) Hα emission line that appears around 20-40 days post-peak. The host-galaxy emission-line ratios indicate the presence of an AGN, though the absence of optical or mid-IR variability and a non-AGN mid-IR color suggest it is weak. AT2021yky exhibits a rapid rise time comparable to that of luminous fast blue optical transients (LFBOTs), while its decay timescale and late-time broad Hα emission resemble those observed in TDEs. However, its cooler blackbody temperature and the absence of He II and Balmer emission lines other than Hα instead favour its classification as an ANT.

The growth rate of cosmic structure, parameterized by fσ_8, is a fundamental test of ΛCDM and general relativity. Using Type Ia supernova (SN Ia) peculiar velocities in conjunction with galaxy redshift surveys may be one of the most precise pathways to measuring fσ_8 in the local Universe, yet existing analyses have not quantified its systematic uncertainties. Here, we present an end-to-end simulated fσ_8 measurement tailored to the Type Ia Supernova Trove from ATLAS in the Nearby Universe (TITAN) survey, using 2000 simulated SNe Ia at z < 0.067. We use the Uchuu N-body simulations to generate mock galaxy catalogs and SN Ia simulations with realistic, correlated peculiar velocities, and use these catalogs to reconstruct density fields that replicate the 2M++ redshift survey. Using a modified forward likelihood framework across eight mock realizations, we recover ⟨ fσ_8 ⟩ = 0.429 ± 0.038 (σ_ stat = 0.030, σ_ sys = 0.023), consistent with the Uchuu simulation input fσ_8 = 0.428 to within 0.1

The present day peculiar velocity-field was sourced by primordial density fluctuations and sculpted over the lifespan of the Universe. Cosmological models such as $Λ$CDM make predictions for various statistical properties of peculiar velocities. Bulk flow, the average velocity within a given volume, has an expectation value of $\vec{0}$ due to isotropy, and a variance directly tied to the Hubble constant, the growth-rate of structure, and the matter power spectrum. In this paper, we use the redshifts and optical and near-infrared distance estimates to Type Ia Supernovae (SNe Ia) within subsets of the Hawai`i Supernova Flows dataset to infer the bulk flow within $z \lesssim 0.1$. The inferred speeds vary between ~100 to 400 km/s but are all consistent with the predictions of $Λ$CDM. As a secondary focus, we discuss the systematic uncertainty introduced by the discrete choice of methodology using two bulk flow estimators, two types of SN Ia distance estimators, and data covering two distinct regimes in wavelength space.

We fit the multi-band light curves of 2,205 Type Ia supernovae (SNe Ia) from the Zwicky Transient Facility DR2 with a one-zone radioactive decay model with a phenomenological addition to include Fe recombination physics. We find a strong correlation between inferred nickel mass and SALT2 stretch, which within our simplified modelling is linked to larger ejecta masses providing longer diffusion times, providing a physical basis for the brighter-slower relation. SN Ia in low-mass hosts (log_10(M_*/M_⊙) < 10) produce 12% more ^56Ni than those in high-mass hosts (ΔM_ Ni = 0.13 M_⊙), linking the host-galaxy mass step to ejecta properties and hinting at metallicity or age-dependent burning efficiencies. This suggests that standardisation based on physical parameters may remove the mass-step. SN 1991T-like events show higher ejecta masses (median 1.64 M_⊙ vs. 1.38 M_⊙ for normals) and produce 30% more ^56Ni, with 84% having super-Chandrasekhar masses. Through Hierarchical modelling of 902 SNe (z ≤ 0.06), we find thermonuclear supernovae can be well described by a Gaussian distribution in ejecta mass and nickel mass with μ_ ej = 1.26 ± 0.01 M_⊙ (σ_ ej = 0.33 ± 0.01 M_⊙) and μ_ Ni = 0.64 ± 0.06 M_⊙ (σ_ Ni = 0.42 ± 0.02 M_⊙), respectively. This leads to inferred fractions of 43 ± 2% sub-M_ Ch (<1.2 M_⊙), 34 ± 1% near-M_ Ch (1.2–1.5 M_⊙), and 24 ± 2% super-M_ Ch (>1.5 M_⊙) events. This work provides a step towards holistic physical characterization of the local SN Ia population, reinforcing the physical basis of SN Ia standardization while quantifying diversity and environmental dependencies critical for understanding progenitor physics and mitigating systematics in precision cosmology.

Astrophysical variabilities of Type Ia supernovae (SNe Ia), such as their link with their birth environment, are now one of the leading sources of systematic uncertainties on the measurement of the dark energy equation-of-state parameter w. Population studies of SNe Ia, using large samples, give precious insights into these variabilities. We analyse a volume-limited subsample of the ZTF SN Ia DR2 with BayeSN, a hierarchical Bayesian model for SN Ia SEDs. We investigate the distributions of SN Ia light curve parameters and their link with SN environment. Using a new training of BayeSN released in a companion paper, we find a smaller scatter of Hubble residuals compared to SALT. We then investigate the magnitude step, which accounts for the correlation between SN Ia standardised absolute magnitude and host environments. We find a posteriori steps of 0.103±0.010 mag (a 10.1σ difference from 0) when using global stellar mass as an environmental proxy, and 0.086±0.010 mag (8.3σ) when using local colour, in accordance with steps computed using SALT light curve fits. This confirms that the large step seen in the ZTF SN Ia DR2 data was not due to the SALT fit or the associated standardisation process. We then investigate the origin of the step, using a BayeSN model which accounts for both an intrinsic magnitude step and differing dust properties with the SN environment. We find a 0.103±0.018 mag (5.6σ) step in global mass and a 0.085±0.019 mag (4.5σ) step in local colour. The means of the R_V distribution are similar between different host environments, with Δ𝔼(R_V)≤0.2 across all environment proxies, with significances ranging from 0.6σ to 1.2σ. This is a strong signal of the existence of an intrinsic dependence of SN Ia absolute magnitude on environment.

We present FlowSN, a statistical framework using simulation-based inference (SBI) with normalizing flows to account for selection effects in observational astronomy. Failure to account for selection effects can lead to biased inference on global parameters. An example is Malmquist bias, where detection limits result in a sample skewed towards brighter objects. In Type Ia supernova (SN Ia) cosmology, these selection effects can systematically shift the inferred posterior distributions of cosmological parameters, necessitating the development of robust statistical frameworks to account for the biases. SBI enables us to implicitly learn probability distributions that are analytically intractable to calculate. In this work, we introduce a novel approach that employs a normalizing flow to learn the non-analytic selected SN likelihood for a given survey from forward simulations, independent of the assumed cosmological model. The resulting likelihood approximation is incorporated into a hierarchical Bayesian framework, and posterior sampling is performed using Hamiltonian Monte Carlo to obtain constraints on cosmological parameters conditioned on the observed data. The modular learnt likelihood approximation can be reused without retraining to evaluate different cosmological models, providing a key advantage over other SBI approaches. We demonstrate the performance of this methodology by training and testing the SBI technique using realistic LSST-like SNANA simulations for the first time. Our FlowSN approach yields accurate posterior estimates on cosmological parameters, including the dark energy equation of state w(0) , that are an order of magnitude less biased than those obtained with conventional techniques and also exhibit improved frequentist calibration.

We present an analysis of ATLAS22kjn (AT 2022fpx), whose high-ionisation coronal lines (CLs) and pre-peak light curve bump provide distinctive opportunities to investigate the physical mechanisms powering tidal disruption events (TDEs). In addition to CLs, the optical spectra show common TDE features, including a strong, blue continuum and broad Balmer and He II lines. The CLs appear before UV/optical light curve peak, preceding the detection of X-rays by ∼ 300 days and persisting after X-rays are no longer detected, suggesting the X-ray emission is obscured at both early and late times. Using the CL luminosities, we constrain the temperature evolution of the ionising source, finding a decrease of ≲ 10 % over 500 days. In the UV/optical light curve, we observe a 9 +4 -2 day bump that peaks 125 +5 -3 rest-frame days before the peak of the main flare. Although we cannot definitively determine the origins of the bump, we find that its timescale and luminosity are most consistent with theoretical predictions for a precursor feature produced by a stream-stream collision or a wind-stream collision. ATLAS22kjn also shows a prominent dust echo in its mid-infrared (MIR) light curves, indicating a high dust covering fraction f_c ≃ 0.40 ± 0.03, similar to the covering fractions of other CL-emitting TDEs. From the multi-wavelength observations of ATLAS22kjn, we estimate the size and relative radii of the emission regions in its nuclear environment and determine that the CL region lies between the broad line region and the MIR-emitting dust. ATLAS22kjn demonstrates the importance of multi-wavelength and early-time observations, and the utility of CLEs in characterising the otherwise unobservable EUV/ultrasoft X-ray emission of TDEs.

We present the class of extreme nuclear transients (ENTs), including the most energetic single transient yet found, Gaia18cdj. Each ENT is coincident with its host-galaxy nucleus and exhibits a smooth (<10% excess variability), luminous (2 × 1045 to 7 × 1045 erg per second), and long-lived (>150 days) flare. ENTs are extremely rare (≥1 × 10-3 cubic gigaparsec per year) compared to any other known class of transients. They are at least twice as energetic (0.5 × 1053 to 2.5 × 1053 erg) as any other known transient, ruling out supernova origins. Instead, the high peak luminosities, long flare timescales, and immense radiated energies of the ENTs are most consistent with the tidal disruption of high-mass ( [Formula: see text] ) stars by massive ( [Formula: see text] ) supermassive black holes (SMBHs). ENTs will be visible to high redshifts (z ~ 4 to 6) in upcoming surveys, providing an avenue to study the high-mass end of the SMBH mass distribution, complementing recent studies of actively accreting SMBHs at high redshifts with the James Webb Space Telescope.

2003fg-like Type Ia supernovae (03fg-like SNe Ia) are rare sub-type of SNe Ia, photometrically characterized by broader optical light curves and bluer ultraviolet (UV) colours compared to normal SNe Ia. In this work, we study four 03fg-like SNe Ia using Swift UltraViolet and Optical Telescope (UVOT) grism observations to understand their unique UV properties and progenitor scenario(s). We report 03fg-like SNe Ia to have similar UV features and elemental compositions as normal SNe Ia, but with higher UV flux relative to optical. Previous studies have suggested that the UV flux levels of normal SNe Ia could be influenced by their progenitor properties, such as metallicity, with metal-poor progenitors producing higher UV flux levels. While 03fg-like SNe were previously reported to occur in low-mass and metal-poor host environments, our analysis indicates that their UV excess cannot be explained by their host-galaxy parameters. Instead, we demonstrate that the addition of a hot blackbody component, likely arising from the interaction with the circumstellar material (CSM), to the normal SN Ia spectrum, can reproduce their distinctive UV excess. This supports the hypothesis that 03fg-like SNe Ia could explode in a CSM-rich environment.

Transient events associated with supermassive black holes provide rare opportunities to study accretion and the environments of supermassive black holes. We present a multiwavelength study of AT2020adpi (ZTF20acvfraq), a luminous optical/UV transient in the nucleus of the galaxy WISEA J231853.77-103505.6 (z=0.26) that exhibits the properties of an ambiguous nuclear transient. Near peak, its spectral energy distribution is well described by a power law ( λ L λ ∝ λ − α , α = 0.44 ± 0.04 ), with a maximum g -band luminosity of ( 3.6 ± 0.6 ) × 10 44 erg s, which is consistent with luminous AGN flares. We detect a strong mid-infrared flare ( L p e a k M I R = ( 2.3 ± 0.05 ) × 10 44 erg s) delayed by ∼ 210 rest-frame days, indicating a hot dust echo from material at ∼ 0.2 pc. The optical and near-infrared spectra show broad H, He I, [OIII] lines, as well as narrow Fe II, and prominent Mg II, which is a combination not typical of TDEs. Taken together, these features suggest AT2020adpi is an ambiguous nuclear transient, where an accretion episode was triggered by stellar disruption of an accretion disk or instabilities within an active nucleus. This source demonstrates the need for careful multiwavelength analysis to distinguish between extreme AGN variability and TDEs.

Type Ia supernovae (SNe Ia) are standardizable candles: their peak magnitudes can be corrected for correlations between light-curve properties and their luminosities to precisely estimate distances. Understanding SN Ia standardization across wavelength improves methods for correcting SN Ia magnitudes. Using 150 SNe Ia from the Foundation Supernova Survey and Young Supernova Experiment, we present the first study focusing on SN Ia standardization properties in the z band. Straddling the optical and near-infrared, SN Ia light in the z band is less sensitive to dust extinction and can be collected alongside the optical on CCDs. Pre-standardization, SNe Ia exhibit less residual scatter in z-band peak magnitudes than in the g and r bands. SNe Ia peak z-band magnitudes still exhibit a significant dependence on light-curve shape. Post-standardization, the z-band Hubble diagram has a total scatter of root mean square=0.195 mag. We infer a z-band mass step of mag, gamma(z)=-0.105 +/- 0.031 which is consistent within 1 sigma of that estimated from gri data, assuming . R-V=2.61. When assuming different R(v )values for high and low mass host galaxies, the z band and optical mass steps remain consistent within 1 sigma . Based on current statistical precision, these results suggest dust reddening cannot fully explain the mass step. SNe Ia in the z band exhibit complementary standardizability properties to the optical that can improve distance estimates. Understanding these properties is important for the upcoming Vera Rubin Observatory and Nancy G. Roman Space Telescope, which will probe the rest-frame z band to redshifts 0.1 and 1.8.

We present a detailed analysis of nearly two decades of optical/UV and X-ray data to study the multi-wavelength pre-explosion properties and post-explosion X-ray properties of nearby SN2023ixf located in M101. We find no evidence of precursor activity in the optical to UV down to a luminosity of less than or similar to 1.0 x 10(5)L(circle dot), while X-ray observations covering nearly 18 yr prior to explosion show no evidence of luminous precursor X-ray emission down to an absorbed 0.3-10.0 keV X-ray luminosity of similar to 6 x 10(36) erg s(-1). Extensive Swift observations taken post-explosion did not detect soft X-ray emission from SN2023ixf within the first similar to 3.3 days after first light, which suggests a mass-loss rate for the progenitor of less than or similar to 5 x 10(-4 )M(circle dot) yr(-1) or a radius of less than or similar to 4 x 10(15) cm for the circumstellar material. Our analysis also suggests that if the progenitor underwent a mass-loss episode, this had to occur > 0.5-1.5 yr prior to explosion, consistent with previous estimates. Swift detected soft X-rays from SN2023ixf similar to 4.25$ days after first light, and it rose to a peak luminosity of similar to 10(39) erg s(-1) after 10 days and has maintained this luminosity for nearly 50 days post first light. This peak luminosity is lower than expected, given the evidence that SN2023ixf is interacting with dense material. However, this might be a natural consequence of an asymmetric circumstellar medium. X-ray spectra derived from merging all Swift observations over the first 50 days are best described by a two-component bremsstrahlung model consisting of a heavily absorbed and hotter component similar to that found using NuSTAR, and a less-absorbed, cooler component. We suggest that this soft component arises from cooling of the forward shock similar to that found in Type IIn SN2010jl.

The study of supernova siblings, supernovae with the same host galaxy, is an important avenue for understanding and measuring the properties of Type Ia Supernova (SN Ia) light curves (LCs). Thus far, sibling analyses have mainly focused on optical LC data. Considering that LCs in the near-infrared (NIR) are expected to be better standard candles than those in the optical, we carry out the first analysis compiling SN siblings with only NIR data. We perform an extensive literature search of all SN siblings and find six sets of siblings with published NIR photometry. We calibrate each set of siblings ensuring they are on homogeneous photometric systems, fit the LCs with the SALT3-NIR and SNooPy models, and find median absolute differences in $\mu$ values between siblings of 0.248 mag and 0.186 mag, respectively. To evaluate the significance of these differences beyond measurement noise, we run simulations that mimic these LCs and provide an estimate for uncertainty on these median absolute differences of $\sim$0.052 mag, and we find that our analysis supports the existence of intrinsic scatter in the NIR at the 99% level. When comparing the same sets of SN siblings, we observe a median absolute difference in $\mu$ values between siblings of 0.177 mag when using optical data alone as compared to 0.186 mag when using NIR data alone. We attribute this to either limited statistics, poor quality NIR data, or poor reduction of the NIR data; all of which will be improved with the Nancy Grace Roman Space Telescope.

A previously unremarkable star near the Canis Major OB1/R1 association underwent an episode of multiple deep brightness minima. Light curves based on archival Gaia, ZTF, NEOWISE data and additional observations from LCO and UKIRT show that the star was not variable prior to 2019 Aug 18 (MJD 58700), and on that date started showing brightness dips of up to 3 magnitudes in the Gaia G and ZTF r bandpasses. After MJD 59500, ~800 days after the onset of these dipping events, the star returned to its previous brightness, and no significant dipping events have been recorded since. Compared to the stable phase, NEOWISE infrared photometry in the W1 and W2 bands indicates a generally redder color, and both decreases and increases in brightness at different times during the dipping episode. The spectrum of Gaia21bcv taken after the end of the dipping episode shows several neutral and ionized metal absorption lines, including Li, indicating a spectral type of ~ K5. Variable emission from [OI] was observed. The H alpha absorption in Gaia21bcv is too faint and irregular for this spectral type, indicating that the line is partly filled in by variable emission, a signature of weak episodic accretion. Gaia21bcv lies above the zero-age main sequence, but is much fainter than typical R CrB stars. We interpret the light curve of Gaia21bcv as being similar to the occultation events in Epsilon Aurigae, i.e., occultation by a disk around a companion object orbiting the primary star.

We present the MULTIMODAL UNIVERSE, a large-scale multimodal dataset of scientific astronomical data, compiled specifically to facilitate machine learning research. Overall, the MULTIMODAL UNIVERSE contains hundreds of millions of astronomical observations, constituting 100 TB of multi-channel and hyper-spectral images, spectra, multivariate time series, as well as a wide variety of associated scientific measurements and "metadata". In addition, we include a range of benchmark tasks representative of standard practices for machine learning methods in astrophysics. This massive dataset will enable the development of large multi-modal models specifically targeted towards scientific applications. All codes used to compile the MULTIMODAL UNIVERSE and a description of how to access the data is available at https://github.com/MultimodalUniverse/MultimodalUniverse

We present extensive observations of the Type II supernova (SN II) SN 2023ufx, which is likely the most metal-poor SN II observed to date. It exploded in the outskirts of a low-metallicity (Z host similar to 0.1 Z circle dot) dwarf (M g = -13.39 +/- 0.16 mag, r proj similar to 1 kpc) galaxy. The explosion is luminous, peaking at M g approximate to -18.5 mag, and shows rapid evolution. The r-band (pseudobolometric) light curve has a shock-cooling phase lasting 20 (17) days followed by a 19 (23) day plateau. The entire optically thick phase lasts only approximate to 55 days following explosion, indicating that the red supergiant progenitor had a thinned H envelope prior to explosion. The early spectra obtained during the shock-cooling phase show no evidence for narrow emission features and limit the preexplosion mass-loss rate to M less than or similar to 10-3 M circle dot yr-1. The photospheric-phase spectra are devoid of prominent metal absorption features, indicating a progenitor metallicity of less than or similar to 0.1 Z circle dot. The seminebular (similar to 60-130 days) spectra reveal weak Fe ii, but other metal species typically observed at these phases (Ti ii, Sc ii, and Ba ii) are conspicuously absent. The late-phase optical and near-infrared spectra also reveal broad (approximate to 104 km s-1) double-peaked H alpha, P beta, and P gamma emission profiles suggestive of a fast outflow launched during the explosion. Outflows are typically attributed to rapidly rotating progenitors, which also prefer metal-poor environments. This is only the second SN II with less than or similar to 0.1 Z circle dot and both exhibit peculiar evolution, suggesting a sizable fraction of metal-poor SNe II have distinct properties compared to nearby metal-enriched SNe II. These observations lay the groundwork for modeling the metal-poor SNe II expected in the early Universe.

We present observations of ASASSN-22ci (AT2022dbl), a nearby tidal disruption event (TDE) discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of d_L ≃ 125 Mpc. Roughly two years after the initial ASAS-SN discovery, a second flare was detected coincident with ASASSN-22ci. UV/optical photometry and optical spectroscopy indicate that both flares are likely powered by TDEs. The striking similarity in flare properties suggests that these flares result from subsequent disruptions of the same star. Each flare rises on a timescale of ∼30 days, has a temperature of ≈30,000 K, a peak bolometric luminosity of L_UV/Opt = 10^43.6 - 43.9 erg s^-1, and exhibits a blue optical spectrum with broad H, He, and N lines. No X-ray emission is detected during either flare, but X-ray emission with an unabsorbed luminosity of L_X = 3×10^41 erg s^-1 and kT = 0.042 eV is observed between the flares. Pre-discovery survey observations rule out the existence of earlier flares within the past ≈6000 days, indicating that the discovery of ASASSN-22ci likely coincides with the first flare. If the observed flare separation of 720 ± 4.7 days is the orbital period, the next flare of ASASSN-22ci should occur near MJD 61075 (2026 February 04). Finally, we find that the existing sample of repeating TDE candidates is consistent with Hills capture of a star initially in a binary with a total mass between ∼1 - 4 M_⊙ and a separation of ∼0.01 - 0.1 AU.

Abstract We present the Multimodal Universe, a new framework collating over 100 TB of multimodal astronomical data for its first release, spanning images, spectra, time series, tabular and hyper-spectral data. This unified collection enables a wide variety of machine learning (ML) applications and research across astronomical domains. The dataset brings together observations from multiple surveys, facilities, and wavelength regimes, providing standardized access to diverse data types. By providing uniform access to this diverse data, the Multimodal Universe aims to accelerate the development of ML methods for observational astronomy that can work across the large differences in astronomical datasets. The framework is actively supported and is designed to be extended whilst enforcing minimal self consistent conventions making contributing data as simple and practical as possible.