Brilliant New Supernova Shatters Cosmic Records For Brightness, Energy, And Even Mass

How does one supernova achieve such extraordinary brightness, energy, and mass? This remains a captivating mystery.

On February 22, 2016, the Pan-STARRS Survey for Transients, a project employing automated telescopes, detected a vibrant signal in the sky, just crossing into the infrared spectrum. Its origin was intriguing, as it emerged from a seemingly empty area of the cosmos devoid of known stars or galaxies, suggesting that any existing galaxy in that region was incredibly faint and far away.

After over three years of detailed analysis, researchers have unveiled what transpired: the most luminous and energetic supernova ever recorded by humanity. According to a study published on April 13, 2020, in Nature Astronomy, this event likely originated from one of the universe's most massive stars, potentially the most massive supernova progenitor observed. This phenomenon holds insights into the earliest supernovae produced by the universe's first stars.

Supernovae generally result from two main pathways. When a star forms, its mass largely dictates its fate:

• If a star has between 8% and 40% of the Sun's mass, it will gradually burn hydrogen, ultimately collapsing into a helium white dwarf.
• A star with 40% to around 800% of the Sun's mass will burn hydrogen, transition into a red giant, and eventually shed its outer layers, culminating in a carbon-and-oxygen white dwarf.
• For stars with a mass exceeding eight times that of the Sun, they will consume hydrogen, helium, carbon, and oxygen until their cores collapse, triggering a supernova explosion.

White dwarfs that accumulate additional mass or merge with another white dwarf can also experience a secondary supernova event.

All supernovae share common characteristics, primarily involving runaway fusion processes where lighter elements combine to form heavier ones, generating a significant portion of the universe's heaviest elements. Typically, they brighten, reach a peak luminosity, and then diminish, with brightness being influenced by their distance from Earth.

Specifically, white dwarf supernovae follow a consistent pattern, enabling astronomers to estimate their distances based on brightness variations. This concept, known as a "standard candle," allows for distance calculations based on intrinsic brightness and redshift.

Standard candles typically emit only about 1% of their energy as visible light and release an energy equivalent to the total output of the Sun over its 10 billion-year lifespan. While this is significant, occasionally, a supernova will emerge that drastically surpasses the norm in brightness and energy: these are termed superluminous supernovae.

The mechanisms behind these extraordinary events remain uncertain. One hypothesis suggests they originate from extremely massive stars that eject material, with the subsequent supernova blast wave colliding with this expelled material. This scenario aligns with the well-known "supernova impostor," Eta Carinae.

Alternatively, superluminous supernovae may result from the pair-instability process. As a star evolves, its core temperature rises with increasing mass. Once a critical threshold is reached, high-energy photon collisions can spontaneously generate particle-antiparticle pairs, notably electrons and positrons.

When this energy threshold is crossed, photons convert into matter, diminishing internal radiation pressure. This leads to further core contraction and heating, causing a cascading reaction that results in a catastrophic explosion.

In January 2020, a groundbreaking study indicated that the pair-instability mechanism does not adequately explain the observed light curves of superluminous supernovae. Instead, they posited that previously ejected material could have enveloped two stellar cores, which merged to create a supernova—this scenario could account for events like SN2006gy.

However, the recent superluminous supernova (SN2016aps) has redefined expectations. Observations and subsequent distance assessments revealed that it emitted over 500 times more energy than typical supernovae, setting a new benchmark.

One might ponder whether this could be another type of transient event. Various cosmic phenomena occur upon stellar demise, such as tidal disruption events, sudden activations of supermassive black holes, or kilonovae from neutron star mergers.

Yet, this event is distinctly different. It showcases a hyper-energetic explosion without signs of tidal disruptions and is offset from its faint host galaxy, negating the possibility of black hole accretion. Its gradual dimming and high hydrogen content eliminate kilonova as a possibility. The evidence indicates this is a superluminous supernova, brighter than any previously recorded.

The research team of 17 scientists conducted simulations to recreate the observed explosion characteristics, arriving at a startling conclusion: this can be modeled as a superluminous supernova, but only if it exceeds all previous records. Specifically:

1. An enormous amount of mass must have been expelled shortly before the explosion, totaling at least tens of solar masses.
2. The star's core must possess more than 50 solar masses of material, heavier than hydrogen, prior to the explosion.
3. The supernova itself must have expelled a vast quantity of material at extraordinary speeds—around 6,000 km/s, or 2% of light speed.

Intriguingly, all scenarios that could recreate these conditions necessitate exceptionally massive stars—those exceeding 100 solar masses. The authors identified two primary pathways to achieve such luminosity: one being a star undergoing a disruptive event followed by a pulsating pair-instability supernova, culminating in a rapidly rotating magnetar at its core; these occurrences are estimated to be as rare as 1 in 10,000 core collapse supernovae.

Alternatively, a massive multi-star system could be involved, where one star experiences a pair-instability supernova while another contributes the surrounding material. This scenario is even rarer, potentially 1 in 50,000, but such environments have been observed nearby, particularly in the Tarantula Nebula within the Large Magellanic Cloud.

Only about a dozen superluminous supernovae have been recorded, and SN2016aps stands unrivaled in terms of absolute brightness. In terms of luminosity, energy output, and the inferred mass of its progenitor star—estimated to exceed 150 solar masses—this supernova is in a league of its own.

There remains a wealth of knowledge to uncover regarding these cosmic phenomena, including whether their afterglows are radioactive, the mass of their progenitors, the nature of their stellar systems, and their occurrence frequency. With the imminent launch of the Vera Rubin Observatory and the James Webb Space Telescope, astronomers will soon have the capability to detect, classify, and analyze these extraordinary events at unprecedented distances, revealing the hidden depths of our cosmic ocean.

Starts With A Bang is now on Forbes, and republished on Medium with a 7-day delay. Ethan has authored two books, *Beyond The Galaxy and Treknology: The Science of Star Trek from Tricorders to Warp Drive.*