Supernovae are the most powerful explosions in the universe. These massive events can occur during the last gasps of a massive star or when a white dwarf is prompted into runaway nuclear fusion. The star, in turn, either collapses upon itself to form a neutron star or black hole. Sometimes it might be just completely annihilated. The top luminosity of a supernova has been compared to that of an entire galaxy.
We now know that these extraordinary events could be partly responsible for life on Earth as we know it.
Evidence published in the scientific journal Geophysical Research Letters demonstrates a close correlation between the fraction of organic matter buried in sediments created by supernovae and changes in their occurrences. This connection indicates that supernovae have set essential conditions for life on Earth to exist.
According to the study, when there are a high number of supernovae, the result can lead to the ingredients for a cold climate, as well as significant temperature differences between the equator and the planet’s polar regions. These differences create high wind speeds and ocean mixing, two very important factors for delivering nutrients to biological ecosystems. High nutrient concentrations lead to greater bioproductivity as well as a more broad burial of organic matter in sediments.
“A fascinating consequence is that moving organic matter to sediments is indirectly the source of oxygen,” said senior researcher Henrik Svensmark of the Technical University of Denmark, lead author of the study. “Photosynthesis produces oxygen and sugar from light, water and CO2. However, if organic material is not moved into sediments, oxygen and organic matter become CO2 and water. The burial of organic material prevents this reverse reaction. Therefore, supernovae indirectly control oxygen production, and oxygen is the foundation of all complex life.”
Over the last 500 million years, supernovae frequency has measured nicely with the concentrations of nutrients on Earth. According to the study, estimating the fraction of organic material found in sediments is achievable by calculating carbon-13 relative to carbon-12. Since life prefers the lighter carbon-12 isotope, the amount of biomass in the world’s oceans changes the ratio between carbon-12 and carbon-13 measured in marine sediments.
While supernovae are now thought to have brought about life on this blue dot, what brings about these explosions capable of traveling at a speedy 9,000 to 25,000 miles (15,000 to 40,000 kilometers) per second? A supernova happens where there is a change in the core of a star. These changes can occur in two different fashions, with both resulting in a really, really big bang.
The first type of supernova occurs in binary star systems. Binary stars are two stars that orbit the same point. One of the stars, a carbon-oxygen white dwarf, steals matter from its companion star. Eventually, the white dwarf accumulates too much matter. Having too much matter causes the star to explode, resulting in a subsequent supernova. The second type of supernova occurs at the end of a single star’s life. As the star’s nuclear fuel gets closer to depletion, some of its mass flows into its core. Eventually, the star’s core is so heavy that it cannot withstand its own gravitational force, forcing it to collapse. This results in the giant explosion of a supernova.
Previous analyses by Svensmark and colleagues have demonstrated that ions help the formation and growth of aerosols, thereby influencing cloud fraction. Since clouds can regulate the solar energy that can reach the Earth’s surface, the cosmic-ray-cloud link is important for climate. Observational evidence shows that the planet’s climate changes when the magnitude of cosmic rays changes. Supernovae frequency can differ by several hundred percent on geological time scales, and the resulting climate changes are extremely noticeable.
“When heavy stars explode, they produce cosmic rays made of elementary particles with enormous energies,” Svensmark said. “Cosmic rays travel to our solar system, and some end their journey by colliding with Earth’s atmosphere. Here, they are responsible for ionizing the atmosphere.”