SN1991ax

SN1991ax is classified as a Type II supernova, consistent with core collapse of a massive star that retained hydrogen in its outer envelope. Typical progenitor mass ranges quoted for the class are model expectations, not a measured mass for this star.

The specific progenitor of SN1991ax 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 SN1991ax.

The distance to SN1991ax has not been measured. No spectroscopic redshift or luminosity distance is published for this transient, so neither its distance from Earth nor its lookback time can be stated. A redshift requires a spectrum, and a photometric redshift requires multi-band imaging that has not been reported. Without a distance, its intrinsic luminosity and total energy release are also undetermined. Check the sources below for follow-up spectroscopy or host-galaxy identification.

No spectroscopic redshift has been measured for SN1991ax. Without a published z, its place in the Hubble flow, recession velocity, and lookback time cannot be stated. A redshift requires a spectrum (or a well-calibrated photometric redshift from multi-band imaging). Check the sources below for follow-up spectroscopy.

At peak brightness, SN1991ax achieved an apparent magnitude of 16.5 around 1991/09/24.

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 SN1991ax.

No ejecta velocity is measured for SN1991ax. 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. Type II events typically show ejecta speeds of order ~8,500 km/s near maximum, but that class scale is not a measurement of SN1991ax.

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 SN1991ax. 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.

Events of SN1991ax's broad spectroscopic class are discussed in galactic chemical evolution as sources of oxygen-group and intermediate-mass elements (and, for some channels, iron-peak material). No measured elemental yields are published for SN1991ax.

A core-collapse explosion associated with SN1991ax'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 SN1991ax. 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.

SN1991ax is associated with cataloged host A030512-4146 at an angular/physical offset of 2.469 from the reported galactic center. That offset places the transient in the host's projected light distribution; it does not by itself prove which stellar population produced the progenitor.

In the celestial sphere, SN1991ax is located at Right Ascension 03:05:12.22 and Declination -41:46:09.8, situated in the constellation Horologium (The Clock). Because its declination is -41:46:09.8, it is favorably placed for Southern Hemisphere observatories.

Along this line of sight, the catalog records a Milky Way foreground color excess of E(B−V) = 0.0114 mag (source: published extinction estimate), corresponding to roughly A_V ≈ 0.04 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.

No calibrated photometry is published for SN1991ax. Without multi-epoch flux measurements, neither a light curve nor a peak magnitude can be established. Follow-up imaging from survey alert streams would be required to map its brightness evolution.

No spectrum has been published for SN1991ax. 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.

SN1991ax was officially reported on 1991/09/15 by McNaught. 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.

Data for SN1991ax are compiled from international astronomical notices, the IAU Transient Name Server (TNS), and peer-reviewed astrophysical journals.

As a core-collapse supernova, SN1991ax provides independent cosmological distance calibrations via the Expanding Photosphere Method (EPM) and the Standard Candle Method for Type II supernovae (SCM-II). By correlating the physical expansion speed of the photosphere (measured via spectroscopic Doppler shifts) with its photometric color temperature, astronomers determine direct geometric distances independent of secondary distance ladders.

Core-collapse supernovae like SN1991ax are premier targets for multi-messenger astrophysics! During the collapse of the iron core, an intense burst of 10⁵⁸ neutrinos escaped into space hours before the shock broke out through the stellar surface (as famously seen in SN 1987A). Furthermore, violent core asymmetries and non-axisymmetric core bounce can emit high-frequency gravitational waves detectable by advanced interferometers (LIGO, Virgo, KAGRA) for events within the Milky Way and Local Group.

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), the distance to SN1991ax is not measured, so no such comparison can be drawn. While historical naked-eye supernovae occurred within our Milky Way or its immediate satellites, modern discoveries like SN1991ax allow astrophysicists to probe diverse galactic environments, metallicities, and stellar populations across the broader universe.

Unknown — no measured brightness. SN1991ax was discovered 12841 days ago (1991/09/15), 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.

Earth is in no danger from SN1991ax. The astrophysical 'lethal kill zone' for a supernova to damage our ozone layer is roughly 50 to 100 light-years. This transient is far outside the solar neighbourhood: it was discovered by a wide-field survey at a magnitude only reachable for an extragalactic object, and any transient in our own galaxy within that radius would have appeared far brighter than the ~18th magnitude reported here. Its exact distance is unmeasured, but the detection brightness alone rules out any nearby threat.