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Potential Life-Threatening Impact: Rare Yet Catastrophic Proximity of Exploding Stars

Stars similar to the sun exhibit remarkable stability in brightness, fluctuating by a mere 0.1 percent over extended periods due to the fusion of hydrogen transforming into helium, which sustains their luminosity. This fusion process ensures a consistent radiance for billions of years until the stars deplete their nuclear fuel, leading to their eventual demise.

When massive stars exhaust their fuel, they undergo a dramatic transformation, expanding and then contracting into a dense stellar type known as a neutron star. However, stars more than eight times larger than the sun meet a more explosive fate in a cataclysmic event known as a supernova.

Supernovae occurrences are infrequent within the Milky Way galaxy, with these violent outbursts typically distant enough not to be perceptible from Earth. For a dying star’s explosion to impact life on Earth, it must go supernova within a proximity of 100 light years.

In astronomical discussions, the narrative often revolves around cosmic threats posed by phenomena like supernovae and their associated effects, such as gamma-ray bursts. While many of these cosmic events remain distant, their proximity to Earth can pose significant risks to life on our planet.

The Spectacle of a Massive Star’s Demise

The occurrence of a supernova, marking the death of a massive star, is a rare cosmic spectacle. When such an event unfolds, it briefly illuminates the cosmos with extraordinary brilliance. With an estimated frequency of one supernova every 50 years and a vast universe to observe, a supernova detonates approximately every hundredth of a second.
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During a supernova event, the dying star emits intense gamma-ray radiation, a high-energy form of electromagnetic radiation invisible to the human eye due to its short wavelengths. Additionally, the star releases a barrage of high-energy particles, including cosmic rays—subatomic particles traveling at near-light speeds.

Although supernovae within the Milky Way are uncommon, historical records document a few instances where these celestial explosions were observable from Earth. In 1054, a sudden bright star appeared in the sky, likely a supernova, which Chinese astronomers also noted in 1006 as a star visible during daylight hours.

The last recorded supernova within the Milky Way occurred in 1604, emphasizing the statistical rarity of such events.

Approximately 600 light years away in the Orion constellation lies a massive star nearing the end of its lifecycle. When this star eventually goes supernova, it will shine as brightly as a full moon from Earth, posing no direct threat to life on our planet.

The Impact of Radiation

If a supernova erupts in close proximity to Earth, the gamma-ray radiation emitted could potentially disrupt the protective shield that enables life to flourish on our planet. Due to the finite speed of light, there exists a time delay in observing such cosmic events. For instance, if a supernova occurs 100 light years away, its effects would only reach Earth after a century.

Evidence of a supernova that exploded 2.5 million years ago, located 300 light years away, has been found in radioactive isotopes preserved in seafloor sediments. The gamma-ray radiation from this event likely affected Earth’s protective ozone layer, leading to climate cooling and contributing to ancient species’ extinction.

The level of safety from supernova impacts increases with greater distance from Earth. As gamma rays and cosmic rays disperse in all directions post-explosion, the radiation reaching Earth diminishes significantly. For instance, a supernova ten times closer to Earth would result in radiation exposure approximately a hundred times stronger compared to a more distant event.

A supernova explosion within 30 light years of Earth would have catastrophic consequences, including severe ozone layer depletion, disruption of marine ecosystems, and potential mass extinctions. Astronomical studies suggest that such nearby supernovae may have triggered extinction events millions of years ago, although these occurrences are exceptionally rare.

Collisions of Neutron Stars

Aside from supernovae, gamma-ray bursts are also generated by the collision of neutron stars, leading to high-energy phenomena spanning the gamma-ray spectrum.

Neutron stars, remnants of supernova explosions, are incredibly dense objects comparable in size to cities but with densities exceeding 300 trillion times that of the sun. When two neutron stars collide, the immense pressure forces atomic nuclei to merge, creating heavier elements like gold and platinum.

The collision of neutron stars produces an intense burst of gamma rays, concentrated into a narrow beam of radiation with significant impact potential.

While the possibility of Earth encountering a gamma-ray burst from a neutron star collision exists, the rarity of such events occurring in pairs reduces the immediate threat. Across the universe, neutron star collisions occur at a frequency of every few minutes.

Although gamma-ray bursts do not currently pose an imminent danger to Earth’s biosphere, the cumulative probability of encountering such events over geological timescales remains inevitable. Studies indicate that Earth has experienced gamma-ray bursts in the past, with a notable occurrence potentially contributing to the Ordovician-Silurian extinction event 440 million years ago.

A Recent Celestial Event

In October 2022, astronomers were confronted with a significant cosmic event as a burst of radiation traversed the solar system, overwhelming gamma-ray telescopes worldwide. This event marked the most intense radiation pulse since the advent of human civilization, originating from an explosion nearly ppp1 light years away.

While life on Earth remained unaffected by this radiation surge, the disturbance it caused in the ionosphere serves as a stark reminder of the potential impact of cosmic phenomena on our planet.