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Type II P Supernova

The Story of Supernova SN2017ejx

An extraordinary stellar explosion that occurred 117.7 Million Light-Years away in deep space.

⏱️ ~9 min deep read 🔬 24 Astrophysical Q&As 🔭 Viewing Guide Included 🪐 Constellation Hydra
🔭 Deep Field (~2.1′ FOV) · Highest-Definition Optical Field (0.25″/pix)
● SN2017ejx Explosion Site

High-magnification deep optical view into SN2017ejx's host environment. Pan and scroll to explore the cosmic neighborhood where this star exploded.

⚡ Quick Observer Facts & Telemetry

IAU Transients DB
🌐 Distance to Earth
117.7 Million Light-Years
Lookback Cosmic Time
✨ Peak Brightness
Mag 15.6
Astro Camera (CCD)
☀️ Peak Radiance
636.2 million Suns
Combined Stellar Energy
🚀 Shock Velocity
~2,420 km/s
~0.8% Speed of Light
🌌 Host Galaxy
NGC 2993
Offset: 0.58″ (0.10 kpc)
🧭 Constellation
Hydra
The Water Snake
💥 Explosion Physics
Type II P
Core-Collapse Supergiant
📅 Discovered On
2017/05/30
ASAS-SN
CHAPTER I

The Iron Core Collapse of a Dying Supergiant

On 2017/05/30, astronomers scanning the heavens flagged a sudden, violent pinpoint of light that had flared into visibility. Designated SN2017ejx, it represents a catastrophic stellar explosion classified as a Type II P supernova.

The progenitor of SN2017ejx was a mammoth supergiant star, shining with the furious vigor of an object at least 8 to 25 times more massive than our Sun. For millions of years, it synthesized heavier and heavier elements in concentric onion-like shells: hydrogen burning into helium, helium into carbon, carbon into oxygen, neon, and silicon. But when silicon fused into iron, the stellar engine ran out of fuel. Iron fusion absorbs energy rather than liberating it; within fractions of a second, the iron core collapsed under its own gravity, rebounding into an immense cosmic shockwave that blasted the star into pieces.

Astrophysical Mechanism Summary
Type: Type II P • Progenitor: Massive Red/Stripped Supergiant Star • Velocity: ~2,420 km/s (~0.8% c)
CHAPTER II

A Message Across Deep Cosmic Time

The light from SN2017ejx is a dispatch from an ancient past. Located approximately 117.7 Million Light-Years away (redshift z = 0.008106), the photons detected by telescopes today began their journey 117.7 million years ago during the Cretaceous period when Tyrannosaurus rex and Triceratops walked the planet.

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 SN2017ejx is to gaze directly into prehistoric cosmic time.

CHAPTER III

Incandescence of 636.2 million Suns

At the height of the outburst around 2017/06/19, SN2017ejx surged to a peak apparent magnitude of 15.6 and an intrinsic absolute magnitude of -17.179. At that instant, this single dying star radiated with the collective power of approximately 636.2 million 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. Over 99% of this energy was emitted within the first 10 seconds as a dense burst of trillions of neutrinos, with only 1% driving the visible blast wave.

CHAPTER IV

The Radioactive Furnace: Why Supernovae Glow for Months

Unlike a conventional terrestrial explosion that cools and goes dark in seconds, SN2017ejx 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.

CHAPTER V

Cosmic Kiln: Seeding the Elements of Life

Supernovae are the premier chemical foundries of our universe. SN2017ejx forged and liberated tons of newly synthesized elements: vast reservoirs of oxygen (the most abundant heavy element in living organisms), carbon, nitrogen, magnesium, and silicon.

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 SN2017ejx billions of years ago.

CHAPTER VI

Galactic Setting in Hydra

SN2017ejx detonated inside NGC 2993, positioned at an offset of 0.58″ (0.10 kpc) from the galactic nucleus. In our terrestrial sky, it resides in the constellation Hydra (The Water Snake) at Right Ascension 09:45:48.610 and Declination -14:22:05.74.

CHAPTER VII

The Scientific Surveillance Campaign

Following its discovery by ASAS-SN, observatories worldwide swung their lenses toward SN2017ejx. In the Open Supernova Catalog, SN2017ejx is documented across 1 photometric measurements and 0 spectroscopic epochs. These multi-wavelength observations allow astrophysicists to model the expanding photosphere, measure shock velocities, and probe circumstellar interactions.

CHAPTER VIII

Stargazer's Field Guide: Can You See It Tonight?

Can I see it tonight? No — this supernova is physically extinguished.

Supernovae are brief, explosive cosmic catastrophes. They brighten over days to weeks and then permanently fade into darkness as their radioactive nickel-56 and cobalt-56 fuel decays. This explosion occurred 9.3 years ago (2017/06/19). Accounting for cosmological time dilation at redshift z = 0.0081, the rest-frame age is +3364.7 days. By standard radioactive decay templates, its optical brightness has decayed by Δm ≈ 34.0 magnitudes to an estimated magnitude 49.6, rendering the transient undetectable to all ground-based observatories.

Instrument Breakdown: At its maximum brightness in 2017/06/19, it reached magnitude 15.60 (Amateur CMOS Rig). Tonight, pointing a telescope at these coordinates will reveal only the background host galaxy (NGC 2993).

Instrument Class & Aperture Sensitivity Limit At Peak Maximum (m=15.60) Tonight (Est. m≈49.6)
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 SN2017ejx was a titanic explosion, our planet sits safely outside the lethal 50–100 light-year kill zone. At a distance of 117.7 Million Light-Years, the blast poses zero physical hazard to Earth's biosphere.

🌌 Cosmic Neighbors & Contemporaries 110,222+ Transients Indexed

Cataloged supernovae closest to SN2017ejx in discovery time, spatial sky neighborhood, and cosmological lookback epoch:

⏱️ Closest in Time
AT2017elz Exploded same day
Type Candidate 2017/05/30 · Mag 17.46
AT2017eru Exploded same day
Type Candidate 2017/05/30 · Mag 16.07
Gaia17bkm Exploded same day
Type Candidate 2017/05/30 · Mag 18.94
🔭 Closest on the Sky
SN2003ao 0.1′ away
Type II Discovered 2003/02/10
AT2020fqf 9.7′ away
Type Candidate Discovered 2020/03/28
AT2021lqi 10.4′ away
Type Candidate Discovered 2021/04/07
🌌 Same Cosmic Era (Redshift)
SN2018yu z = 0.008112
Type Ia ~111.1 Mly lookback
SN1993X z = 0.0081
Type II ~111.0 Mly lookback
SN1998dg z = 0.0081
Type Ia ~111.0 Mly lookback

❓ Frequently Asked Questions About SN2017ejx

Scientific & observational Q&As indexed from astronomical databases & the Open Supernova Catalog
🔍 24 of 24
What type of supernova is SN2017ejx and what kind of star exploded? Astrophysics & Progenitor
SN2017ejx is a Type II Core-Collapse Supernova, marking the death of an evolved red supergiant star (with an initial mass between 8 and 25 times our Sun) that preserved its vast outer hydrogen envelope. Having exhausted all nuclear fuel through successive stages of fusion (hydrogen, helium, carbon, neon, oxygen, and silicon), its inert iron core could no longer withstand gravitational pressure. In less than a quarter of a second, the iron core collapsed into nuclear density, triggering a catastrophic outward shockwave that blasted the star's outer layers into interstellar space.
What was the progenitor star doing in the millions of years leading up to SN2017ejx? Astrophysics & Progenitor
Before detonating as SN2017ejx, the progenitor lived a short, furious stellar life of roughly 10 to 30 million years. In its interior, temperatures and pressures reached astronomical extremes, burning through nuclear fuel in an 'onion-skin' arrangement of concentric shells: hydrogen burning into helium for millions of years, helium into carbon for hundreds of thousands of years, carbon into neon for centuries, oxygen into silicon for months, and silicon fusing into iron in mere days! Once iron filled the core, fusion could no longer extract energy, dooming the star to sudden gravitational collapse.
How far away is SN2017ejx from Earth and how old is the light reaching us? Cosmic Distance & Time
SN2017ejx is located approximately 117.7 Million Light-Years from Earth (cosmological redshift z = 0.008106, luminosity distance d_L = 36.097). Because electromagnetic radiation travels at 299,792 km/s, the photons detected by modern telescopes began their cosmic voyage 117.7 million years ago during the Cretaceous period when Tyrannosaurus rex and Triceratops walked the planet. While that light traveled across intergalactic space, Earth's continents shifted and biological evolution shaped the history of our planet.
What does the cosmological redshift of SN2017ejx tell us about the expansion of space? Cosmic Distance & Time
SN2017ejx exhibits a measured spectroscopic redshift of z = 0.0081. Under Hubble's Law, this redshift corresponds to an apparent recessional velocity of approximately 2,430.1 km/s away from our Milky Way galaxy. This redshift is not motion through space alone, but the stretching of light waves as the fabric of the universe itself expanded during the millions of years the photons traveled to our telescopes.
How bright did SN2017ejx become at its peak, and how many Suns does that equal? Explosion Energetics
At peak brightness, SN2017ejx achieved an apparent magnitude of 15.6 around 2017/06/19. Corrected for cosmic distance and foreground interstellar dust, its intrinsic absolute magnitude was -17.179. At this peak, the exploding star radiated with the incandescent brilliance of approximately 636.2 million Suns combined, briefly outshining the cumulative starlight of entire dwarf galaxies!
How much total energy was released by SN2017ejx, and where did that energy go? Explosion Energetics
The collapse of SN2017ejx's progenitor released a staggering 10⁵³ ergs of gravitational binding energy—more energy than our Sun will radiate across its entire 10-billion-year lifespan! Astonishingly, 99% of this titanic energy was emitted within 10 seconds in the form of trillions of nearly massless neutrinos. Only about 1% (10⁵¹ ergs) drove the physical kinetic blast wave, and a mere 0.01% (10⁴⁹ ergs) was radiated as the visible starlight observed by telescopes.
How fast are the supernova ejecta and shockwave of SN2017ejx expanding through space? Explosion Energetics
The debris and shockwave of SN2017ejx erupted into space at an astounding velocity of approximately 2,420 km/s (measured spectroscopically). This corresponds to roughly 0.8% of the speed of light (Mach 7,055 in air)! At this blistering speed, the expanding debris shell traverses the entire diameter of planet Earth in just 5.27 seconds, carving a giant bubble in the interstellar medium.
What powers the prolonged glow of SN2017ejx weeks and months after detonation? Radioactive Engine
While the initial flash of SN2017ejx was driven by shock breakout heating through the stellar envelope, its prolonged visibility over weeks and months was sustained by the radioactive decay of approximately 0.05 to 0.15 solar masses of Nickel-56 (⁵⁶Ni) forged in the core shock. As ⁵⁶Ni decays into ⁵⁶Co (half-life: 6.1 days) and then into stable ⁵⁶Fe (half-life: 77.2 days), gamma rays and positrons thermalize within the expanding ejecta, preventing the debris from instantly freezing in the vacuum of space.
What chemical elements did SN2017ejx create and disperse into the universe? Nucleosynthesis & Elements
Core-collapse supernovae like SN2017ejx are the primary creators of life-sustaining elements in the cosmos. The explosion manufactured and dispersed immense reservoirs of oxygen (the single most abundant heavy element in the universe), alongside carbon, nitrogen, neon, magnesium, silicon, sulfur, and calcium (which builds terrestrial bones and teeth). In the ultra-dense, neutron-rich shockwave, rapid neutron capture (r-process nucleosynthesis) forged heavy elements like gold, platinum, and uranium.
Did SN2017ejx leave behind a black hole, a neutron star, or nothing at all? Cosmic Remnant
The crushing core collapse of SN2017ejx's progenitor forged 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.
What will SN2017ejx's explosion site look like in 1,000 to 10,000 years? Cosmic Remnant
Over the coming millennia, the explosion site of SN2017ejx will undergo three dramatic evolutionary epochs: During the next few centuries (Free Expansion phase), the ejecta shell will continue expanding at thousands of km/s. Between 500 and 10,000 years (the Sedov-Taylor adiabatic phase), the forward shock will sweep up hundreds of solar masses of interstellar gas, heating it to tens of millions of degrees and glowing in bright thermal X-rays (similar to the famous Cygnus Loop or Cassiopeia A). Eventually, the cooling shock will compress nearby giant molecular clouds, triggering the gravitational collapse of new stars and solar systems!
In which galaxy did SN2017ejx explode, and where is it located relative to the galactic center? Galactic Environment
SN2017ejx occurred in NGC 2993, located at an offset of 0.58″ (0.10 kpc) from the galactic nucleus. In optical and infrared imaging, this positions the explosion within the galaxy's active stellar disk or spiral arms, where ongoing star formation constantly generates massive short-lived stellar progenitors.
Where is SN2017ejx located in the night sky and which constellation is it in? Sky Coordinates
In the celestial sphere, SN2017ejx is located at Right Ascension 09:45:48.610 and Declination -14:22:05.74, situated in the constellation Hydra (The Water Snake). Because its declination is -14:22:05.74, it is favorably placed for Southern Hemisphere observatories.
How much Milky Way interstellar dust obscures our view of SN2017ejx? Interstellar Dust
Light from SN2017ejx passed through interstellar dust in the Milky Way, suffering a foreground color excess of E(B-V) = 0.052 magnitudes (based on Schlafly & Finkbeiner 2011 galactic recalibrations). This cosmic dust absorbs and scatters shorter blue wavelengths, dimming the transient by approximately A_V ≈ 0.16 magnitudes in visual light.
Across which photometric filter bands was SN2017ejx monitored? Astronomical Observations
SN2017ejx was tracked across 1 photometric observations utilizing filter bands including optical filters. Data were captured by observatories and survey networks including global optical observatories. Multi-color photometry tracks the temperature evolution of the fireball, verifying the rise time to peak and the rate of radioactive decline.
What did astronomical spectroscopy reveal about SN2017ejx's chemical makeup? Astronomical Observations
Spectroscopic observations of SN2017ejx confirmed its astrophysical classification by dissecting its light into individual wavelengths. Absorption and emission line features reveal the chemical composition, expansion velocity, and temperature of the expanding fireball.
Who discovered SN2017ejx and how was it first detected? Discovery & History
SN2017ejx was officially reported on 2017/05/30 by ASAS-SN. 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.
How many scientific publications and observatories have contributed data to SN2017ejx? Scientific Research
SN2017ejx is documented across 7 scientific references and archival data sources in the Open Supernova Catalog. These include discovery circulars and research datasets from 2016A&A...594A..13P, 2011ApJ...737..103S, ATel 10463, ASAS-SN Supernovae. All raw photometry and spectroscopy points are cross-indexed to their original bibliographic records for peer-reviewed verification.
What other names and survey identifiers exist for SN2017ejx? Cross-Identifications
Throughout global alert streams and survey databases, SN2017ejx has also been designated as: AT2017ejx, ASASSN-17he. 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).
How does SN2017ejx contribute to measuring the Hubble Constant and the scale of the cosmos? Cosmology & Distance Ladder
As a core-collapse supernova, SN2017ejx 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.
Could gravitational waves or neutrinos from SN2017ejx be detected on Earth? Multi-Messenger Astronomy
Core-collapse supernovae like SN2017ejx 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.
How does SN2017ejx compare to famous historical supernovae like SN 1987A or the Crab Supernova? Historical Comparison
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), SN2017ejx occurred at a distance of 117.7 Million Light-Years. While historical naked-eye supernovae occurred within our Milky Way or its immediate satellites, modern discoveries like SN2017ejx allow astrophysicists to probe diverse galactic environments, metallicities, and stellar populations across the broader universe.
Can I see SN2017ejx tonight with a backyard telescope or binoculars? Backyard Observation
SN2017ejx exploded 9.3 years ago (2017/05/30). Optical transient emission has completely faded along its radioactive decay curve. Today, pointing a telescope at these coordinates reveals the expanding remnant nebula or NGC 2993; the original optical transient is no longer detectable with amateur backyard equipment.
Does the radiation or shockwave from SN2017ejx pose any threat to Earth? Planetary Safety
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 117.7 Million Light-Years, the inverse-square law dilutes the radiation by quintillions of times, making SN2017ejx completely harmless to our biosphere and purely a fascinating spectacle for human exploration.
Data sourced from IAU TNS, ALeRCE, WISeREP, and the Open Supernova Catalog. View All General Astrophysics FAQs →
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