AT2025tmm

AT2025tmm is cataloged as a Type Galaxy transient. Mechanism-specific claims (progenitor mass, nickel yield, remnant type) require more than this label and are not asserted here as object-specific measurements.

The specific progenitor of AT2025tmm has not been observed. Events of this spectroscopic class are generally associated with massive-star core collapse after successive nuclear burning stages (hydrogen → helium → carbon → neon → oxygen → silicon → iron). Typical lifetimes of such progenitors are tens of millions of years, but that is a class expectation—not a measured age or evolutionary track for this star. No pre-explosion imaging identification is cited in the available record for AT2025tmm.

AT2025tmm has a luminosity distance of approximately 1231.8 Million Light-Years (redshift z = 0.083, d_L = 377.67 Mpc). Under a flat ΛCDM cosmology (H₀≈70 km/s/Mpc, Ωₘ≈0.3), the corresponding lookback time is ≈1093 Myr — when the light set out 1092.9 million years ago in deep Precambrian time, well before multicellular animals dominated Earth. Luminosity distance is larger than the light-travel distance because cosmic expansion stretches the path; the two must not be equated.

AT2025tmm exhibits a measured spectroscopic redshift of z = 0.0830. The cockpit reports a user-facing recession velocity of 23,853.4 km/s, computed as the redshift Doppler-equivalent v = c·((1+z)²−1)/((1+z)²+1). Cosmological redshift is not generally equivalent to special-relativistic motion through space; this number is a convenient velocity label for z, not a measured peculiar velocity and not supernova ejecta speed. Bare c·z (≈24,883 km/s) is a different low-z approximation and is not mixed here.

Observed (single-epoch) magnitude of AT2025tmm is 19.01 (r) on 2025/08/11 (MJD 60898.3). A single calibrated detection is not evidence of a peak; no rise, decline, or light curve can be established from one point. An absolute magnitude of -18.88 mag can be quoted only if distance is independently known.

Core-collapse events of this broad class are often discussed with a ~10⁵³ erg gravitational binding energy of which ~99% may escape as neutrinos—again a class scale, not a measured budget for AT2025tmm.

No ejecta velocity is measured for AT2025tmm. Blast-wave speed is obtained from Doppler shifts of spectral absorption features (e.g. Si II λ6355 for Type Ia), not from cosmological redshift. Any recession velocity derived from z describes Hubble flow, not the explosion debris.

Classified core-collapse light curves are often sustained after peak by radioactive ⁵⁶Ni → ⁵⁶Co → ⁵⁶Fe decay, with typical nickel yields of order 0.05–0.15 solar masses—again a class scale, not a measured yield for AT2025tmm. Shock-breakout heating may dominate the earliest optical flash; without a published bolometric fit, neither nickel mass nor the dominant power source is established for this event.

The nucleosynthetic products of AT2025tmm are unknown because its type is unresolved. Element yields depend directly on the explosion mechanism: a thermonuclear Type Ia produces mostly iron-peak elements such as ⁵⁶Ni and ⁵⁶Fe, whereas a core-collapse event produces large quantities of oxygen, neon, magnesium and silicon from successive burning shells. No spectrum has been published for this transient, so which of these occurred is not established.

A core-collapse explosion associated with AT2025tmm's class forges an ultra-dense compact stellar remnant at the center of the detonation. If the progenitor had an initial mass under ~20 solar masses, it left behind a neutron star (pulsar)—packing the mass of our entire Sun into a city-sized sphere barely 20 kilometers wide, spinning dozens or hundreds of times per second. If the progenitor exceeded ~25–30 solar masses, gravity overcame neutron degeneracy pressure, creating a permanent stellar-mass black hole.

Supernova remnants in general evolve through free-expansion, Sedov–Taylor, and radiative phases over centuries to millennia, sometimes becoming bright X-ray shells and occasionally compressing nearby molecular clouds. These are standard remnant-evolution models, not forecasts measured for AT2025tmm. Whether this site will trigger star formation, reach particular X-ray temperatures, or match Cassiopeia A depends on local density and magnetic field—none of which are constrained by the data shown here.

No host galaxy is identified for AT2025tmm in this catalog record. A blank host field means the association is unresolved here—it does not establish that the host is uncataloged, resolved in imaging, or securely linked by astrometry. Possible states (unidentified, hostless candidate, imaging detection without a catalog name, or a securely matched cataloged galaxy) require separate evidence that is not present in this field.

In the celestial sphere, AT2025tmm is located at Right Ascension 15:44:21.888 and Declination +19:13:43.83, situated in the constellation Corona Borealis (The Northern Crown). Because its declination is +19:13:43.83, it is primarily placed in the Northern celestial hemisphere.

Along this line of sight, the catalog records a Milky Way foreground color excess of E(B−V) = 0.0436 mag (source: Analytical Galactic Disk Model (IAU)), corresponding to roughly A_V ≈ 0.14 mag for R_V = 3.1. Band-specific corrections (e.g. A_r) differ from A_V and should be applied when available. Map-based values (IRSA / Schlafly & Finkbeiner 2011) must not be claimed unless that map was actually queried.

AT2025tmm has 1 calibrated photometric detection on record in r from YSE. A single point is not a light curve: no rise, peak, or decline rate can be measured until additional epochs are published.

No spectrum has been published for AT2025tmm. Without spectroscopy, its chemical composition, expansion velocity, and physical classification cannot be established. Classification spectra from follow-up observatories would be required to identify diagnostic absorption and emission lines.

AT2025tmm was officially reported on 2025/08/11 by D. O. Jones (UC Santa Cruz), K. D. French (Carnegie, Illinois), A. Agnello, Z. Ansari, N. Arendse, C. Gall, C. Grillo, S. H. Bruun, C. Hede, J. Hjorth, L. Izzo, H. Korhonen, S. Raimundo, D. Kodi Ramanah, A. Sarangi, R. Wojtak, H. Pfister (DARK, U Copenhagen), K. Auchettl (DARK, UC Santa Cruz, U Melbourne), K. C. Chambers, M. E. Huber, E. A. Magnier, T. J. L. de Boer, J. R. Fairlamb, C. C. Lin, R. J. Wainscoat, T. Lowe, G. Paek, A. S. B. Schultz, P. Minguez (IfA, Hawaii), A. Engel, A. Gagliano, G. Narayan, M. Soraisam (Illinois), Q. Wang (JHU), A. Rest (JHU, STScI), S. J. Smartt, K. W. Smith (Oxford / QUB), C. R. Angus (QUB), K. Alexander, P. Blanchard, L. DeMarchi, A. Hajela, W. Jacobson-Galan, R. Margutti, D. Matthews, C. Stauffer, M. Stroh (Northwestern), M. Drout (U Toronto), D. A. Coulter, G. Dimitriadis, R. J. Foley, T. Hung, C. D. Kilpatrick, C. Rojas-Bravo, M. R. Siebert (UC Santa Cruz), E. Ramirez-Ruiz (UC Santa Cruz, DARK). Discoveries are typically flagged by high-cadence robotic survey telescopes (such as ATLAS, ZTF, Pan-STARRS, ASAS-SN, or Gaia) and worldwide amateur astronomers scanning the night sky, followed by rapid spectroscopic classification by international observatories.

AT2025tmm is documented across 3 scientific references and archival data sources in the sne.space. These include discovery circulars and research datasets from Transient Name Server, 2025TNSTR3144....1J, The Open Supernova Catalog. All raw photometry and spectroscopy points are cross-indexed to their original bibliographic records for peer-reviewed verification.

Throughout global alert streams and survey databases, AT2025tmm has also been designated as: 2025tmm, PS25gdi, GOTO25ftr, SN2025tmm, AT 2025tmm, ATLAS25jll. These cross-matched identifiers allow astronomers to cross-reference observations across the Zwicky Transient Facility (ZTF), the Asteroid Terrestrial-impact Last Alert System (ATLAS), Pan-STARRS, Gaia Photometric Science Alerts, and the IAU Transient Name Server (TNS).

AT2025tmm cannot currently be used for cosmological distance work because its classification is unresolved. The distance ladder relies on type-specific techniques: Type Ia supernovae use the Phillips relation between peak absolute magnitude and decline rate, while Type II events use the Expanding Photosphere Method or SCM-II. An unclassified transient fits neither, so no Hubble-constant constraint can be derived from it until a spectrum establishes its type.

No neutrino or gravitational-wave counterpart has been reported for AT2025tmm, and none is expected to be identifiable without a classification. The multi-messenger signature differs sharply by type: core-collapse events emit a neutrino burst at shock breakout (detected once, for SN 1987A), while thermonuclear Type Ia events produce negligible neutrinos and gravitational waves. Searching for a counterpart before knowing which mechanism applies would be unfocused.

Compared to historical landmarks like SN 1987A in the Large Magellanic Cloud (168,000 light-years away, naked-eye peak m = 2.9) or the Crab Supernova of 1054 (6,500 light-years away), AT2025tmm occurred at a distance of 1231.8 Million Light-Years. While historical naked-eye supernovae occurred within our Milky Way or its immediate satellites, modern discoveries like AT2025tmm allow astrophysicists to probe diverse galactic environments, metallicities, and stellar populations across the broader universe.

Unknown — no measured brightness. AT2025tmm was discovered 461 days ago (2025/08/11), but no calibrated photometry is published for it, so its current apparent magnitude cannot be stated. Without a magnitude there is no basis for a telescope-aperture recommendation. Use the coordinates and airmass chart above to plan a follow-up observation and report what you measure.

No, Earth is in zero danger. Supernovae are violent events emitting powerful gamma rays, X-rays, and cosmic rays; however, the astrophysical 'lethal kill zone' for our planet's protective ozone layer is estimated at 50 to 100 light-years. At a distance of 1231.8 Million Light-Years, the inverse-square law dilutes the radiation by quintillions of times, making AT2025tmm completely harmless to our biosphere and purely a fascinating spectacle for human exploration.