High-magnification deep optical view into SN1991S's host environment. Pan and scroll to explore the cosmic neighborhood where this star exploded.
★ Benchmark Astrophysical Landmark
SN1991S is recognized as one of the definitive benchmark supernovae in modern astrophysics. Due to its exceptional peak luminosity, favorable host galaxy orientation, and rapid multi-messenger follow-up, it was extensively observed across the electromagnetic spectrum by premier facilities—including space telescopes (HST, JWST, Swift) and global ground-based spectroscopic networks. It provides foundational empirical constraints for stellar progenitor models, ejecta dynamics, and cosmological distance calibrations.
⚡ Quick Observer Facts & Telemetry
IAU Transients DBThe Thermonuclear Obliteration of a White Dwarf
On 1991/04/10, astronomers scanning the heavens flagged a sudden, violent pinpoint of light that had flared into visibility. Designated SN1991S, it represents a catastrophic stellar explosion classified as a Type Ia supernova.
In a binary star system located deep within UGC 5691, a dense carbon-oxygen white dwarf—the dead stellar corpse of an ancient sun—orbited its stellar companion for millions of years. As it siphoned material across the gravitational saddle point, its mass relentlessly climbed toward the Chandrasekhar limit of 1.4 solar masses. At that fateful tipping point, uncontrollable carbon fusion ignited in the degenerate core, ripping the entire star apart in a thermonuclear detonation that left behind zero remnant.
A Message Across Deep Cosmic Time
The light from SN1991S is a dispatch from an ancient past. Located approximately 773.0 Million Light-Years away
(redshift z = 0.055001), the photons detected by telescopes today began their journey
773.0 million years ago during the Paleozoic era, long before the first dinosaurs appeared on Earth.
While this burst of electromagnetic radiation traversed the cold void of intergalactic space at 299,792 kilometers per second, continents on Earth drifted, mountain ranges rose, and entire ecosystems rose and fell. To look into a telescope at SN1991S is to gaze directly into prehistoric cosmic time.
Incandescence of 2.9 billion Suns
At the height of the outburst around 1991/04/01, SN1991S surged to a peak apparent magnitude of 17.99 and an intrinsic absolute magnitude of -18.83. At that instant, this single dying star radiated with the collective power of approximately 2.9 billion Suns combined, outshining whole dwarf galaxies and illuminating the surrounding interstellar medium.
The total energy released by the cataclysm was on the order of 10⁵¹ to 10⁵³ ergs. Virtually all of this was deposited into the kinetic shockwave and radioactive nucleosynthesis.
The Radioactive Furnace: Why Supernovae Glow for Months
Unlike a conventional terrestrial explosion that cools and goes dark in seconds, SN1991S shone brightly for weeks and months. The secret behind this prolonged celestial glow is nuclear physics: the extreme heat and pressure of detonation synthesized vast quantities of radioactive Nickel-56 (⁵⁶Ni).
With a half-life of 6.075 days, Nickel-56 decays into Cobalt-56 (⁵⁶Co), emitting gamma rays and high-energy positrons that heat the expanding ejecta from within. Cobalt-56 in turn decays with a half-life of 77.2 days into stable Iron-56 (⁵⁶Fe), powering the steady exponential radioactive tail observed in the light curve.
Cosmic Kiln: Seeding the Elements of Life
Supernovae are the premier chemical foundries of our universe. SN1991S forged and liberated tons of newly synthesized elements: rich supplies of iron, silicon, calcium, and sulfur that will one day seed the formation of rocky terrestrial worlds.
As Carl Sagan famously observed, "We are made of star-stuff." The iron atoms that carry oxygen in human hemoglobin and the calcium in our bones were originally forged in explosions identical to SN1991S billions of years ago.
Galactic Setting in Leo
SN1991S detonated inside UGC 5691, positioned at an offset of 17.05″ (12.69 kpc) from the galactic nucleus.
In our terrestrial sky, it resides in the constellation Leo (The Lion) at Right Ascension 10:29:27.7
and Declination +22:00:43.
The Scientific Surveillance Campaign
Following its discovery by Antezana, observatories worldwide swung their lenses toward SN1991S.
In the Open Supernova Catalog, SN1991S is documented across 65 photometric measurements
in passbands such as B, I, R, V and 2 spectroscopic epochs.
These multi-wavelength observations allow astrophysicists to model the expanding photosphere, measure shock velocities, and probe circumstellar interactions.
Stargazer's Field Guide: Can You See It Tonight?
Can I see it tonight? Only as an expanding historical remnant.
The optical supernova exploded 35 years ago (1991/04/01). The bright transient outburst has long since ceased, leaving behind an expanding gaseous shell or pulsar wind nebula emitting in radio, X-rays, and faint nebular optical lines.
Historical Maximum: At peak in 1991/04/01, it reached magnitude 17.99 (Amateur CMOS Rig). Pointing here tonight observes the host galaxy (UGC 5691).
| Instrument Class & Aperture | Sensitivity Limit | At Peak Maximum (m=17.99) | Tonight (Est. m≈203.9) |
|---|---|---|---|
| Naked Eye Dark sky site (Bortle 1–3) with no optical aid |
m ≤ 6.0 | ❌ Below limit | ❌ Below limit |
| Binoculars (50mm) Standard 7x50 or 10x50 handheld binoculars |
m ≤ 9.5 | ❌ Below limit | ❌ Below limit |
| Small Backyard Scope (4" / 100mm) Entry 4-inch (100mm) refractor / reflector |
m ≤ 12.0 | ❌ Below limit | ❌ Below limit |
| Medium Amateur Scope (8"–12") 8-inch to 12-inch Dobsonian or Schmidt-Cassegrain |
m ≤ 14.5 | ❌ Below limit | ❌ Below limit |
| Amateur CMOS Rig Cooled monochrome/color CMOS camera with multi-hour stack |
m ≤ 19.5 | ✅ Detectable | ❌ Below limit |
| 2m–3m Research Telescope University or regional observatory (e.g. Palomar 60", Calar Alto) |
m ≤ 22.0 | ✅ Detectable | ❌ Below limit |
| Giant 8m–10m Observatories Keck (10m), VLT (8.2m), Gemini, Subaru optical imaging |
m ≤ 25.0 | ✅ Detectable | ❌ Below limit |
| Space Observatories Only Hubble Space Telescope (WFC3) / JWST (NIRCam deep stack) |
m ≤ 30.0 | ✅ Detectable | ❌ Below limit |
Planetary Safety Note: Even though SN1991S was a titanic explosion, our planet sits safely outside the lethal 50–100 light-year kill zone. At a distance of 773.0 Million Light-Years, the blast poses zero physical hazard to Earth's biosphere.
Cataloged supernovae closest to SN1991S in discovery time, spatial sky neighborhood, and cosmological lookback epoch:
❓ Frequently Asked Questions About SN1991S
What type of supernova is SN1991S and what kind of star exploded? Astrophysics & Progenitor
What was the progenitor star doing in the millions of years leading up to SN1991S? Astrophysics & Progenitor
How far away is SN1991S from Earth and how old is the light reaching us? Cosmic Distance & Time
What does the cosmological redshift of SN1991S tell us about the expansion of space? Cosmic Distance & Time
How bright did SN1991S become at its peak, and how many Suns does that equal? Explosion Energetics
How much total energy was released by SN1991S, and where did that energy go? Explosion Energetics
How fast are the supernova ejecta and shockwave of SN1991S expanding through space? Explosion Energetics
What powers the prolonged glow of SN1991S weeks and months after detonation? Radioactive Engine
What chemical elements did SN1991S create and disperse into the universe? Nucleosynthesis & Elements
Did SN1991S leave behind a black hole, a neutron star, or nothing at all? Cosmic Remnant
What will SN1991S's explosion site look like in 1,000 to 10,000 years? Cosmic Remnant
In which galaxy did SN1991S explode, and where is it located relative to the galactic center? Galactic Environment
Where is SN1991S located in the night sky and which constellation is it in? Sky Coordinates
How much Milky Way interstellar dust obscures our view of SN1991S? Interstellar Dust
Across which photometric filter bands was SN1991S monitored? Astronomical Observations
B, I, R, V. Data were captured by observatories and survey networks including Danish 1.54m, ESO 3.6m, MPG/ESO 2.2m. Multi-color photometry tracks the temperature evolution of the fireball, verifying the rise time to peak and the rate of radioactive decline.