Space
Evidence found deep beneath the Pacific Ocean suggests that an ancient supernova may have unleashed cosmic rays towards Earth. Researchers have begun to identify the potential sources of this celestial event.
By Alex Wilkins
A supernova could have sent cosmic rays hurtling at Earth
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According to recent findings, an explosion of a distant star may have propelled cosmic rays towards Earth approximately 10 million years ago. Astronomers have identified the possible candidates behind this stellar event.
Earlier this year, Dominik Koll and his research team at the Helmholtz-Zentrum Dresden-Rossendorf, Germany, discovered an unusual spike in radioactive beryllium nestled within metallic rock formations buried 5 kilometers beneath the Pacific Ocean. After dating the beryllium, they estimated it to be just over 10 million years old. This type of beryllium forms when cosmic rays collide with Earth’s atmosphere, prompting the researchers to speculate that a supernova could have been the cause.
However, other hypotheses have emerged, including possibilities that the Sun’s magnetic field may have been weaker during this period, or that ocean currents from the poles, which have a stronger presence of cosmic rays, could have participated in beryllium’s deposition.
Recently, Efrem Maconi from the University of Vienna and his collaborators utilized data from the Gaia space telescope, which has meticulously mapped the current locations and movements of billions of stars within the Milky Way.
By retracing the orbits of approximately 2,700 star clusters relative to the sun over 20 million years, they calculated the likelihood of supernova occurrences in those clusters. Their findings indicated a 70 percent probability that a star exploded within 300 light-years of Earth at the time of the beryllium spike, with a 30 percent chance that no such supernova transpired.
The researchers identified two promising candidates for the supernova explosion, should one have indeed occurred. The foremost contender is a youthful cluster named ASCC 20, located within approximately 200 light-years. The second candidate is the cluster known as OCSN 61, situated further away.
Furthermore, geological evidence from 10 million years ago suggests that the solar system was moving through a denser region of the galaxy, involved in a vast wave of gas, dust, and other stars referred to as the Radcliffe Wave.
“This urges us to investigate further,” Koll commented. “If Maconi had claimed we could categorically rule out any supernova candidates, I would have regarded that as a definitive conclusion. However, this intriguing possibility remains open.”
Koll asserts that additional modeling of the stars’ movements is necessary to ascertain whether a star was indeed responsible for the cosmic influx. This theory harmonizes with previous geological records indicating a spike in radioactive isotopes from cosmic dust around 7.5 million years ago. Since cosmic dust disperses more slowly than cosmic rays, which travel close to the speed of light, it is plausible that the spike in beryllium occurred when cosmic rays first struck Earth, while the associated dust reached our planet millennia later, albeit confirming this hypothesis could prove difficult.
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