Dust on Ocean Seabed May Come From Stellar Explosion

When we picture the ocean floor, we might see lots of smooth sand, colorful corals, and schools of fish swimming in unison. We would hardly imagine extraterrestrial bits from far-away space raining down and settling on the bottom, and yet that's exactly what some scientists are saying. Though despite previous belief, dust found on the ocean seabed may not in fact come from supernovae, according to a new study, shedding light on these stellar explosions.

Current theories of supernovae - eruptions outside of our solar system bright enough to outshine an entire galaxy - suggest that these events eject into space materials essential for human life, such as iron, potassium and iodine, as well as lead, silver, gold, and heavier radioactive elements like uranium and plutonium.

However, the report published in the journal Nature Communications is at odds with this hypothesis, and is raising new questions about supernovae.

"Small amounts of debris from these distant explosions fall on the Earth as it travels through the galaxy," lead researcher Dr. Anton Wallner, from Australian National University, said in a statement. "We've analyzed galactic dust from the last 25 million years that has settled on the ocean and found there is much less of the heavy elements such as plutonium and uranium than we expected."

Wallner and his colleagues focused on plutonium-244, which has a half-life of 81 million years (the time it takes for the material's radioactivity to decay by half its original value).

The researchers studied deep-sea sediment samples and a 10-centimeter slab taken from the Earth's crust, looking for any signs of plutonium-244 as intergalactic dust built up within the last 25 million years.

"We found 100 times less plutonium-244 than we expected," Wallner said. "It seems that these heaviest elements may not be formed in standard supernovae after all. It may require rarer and more explosive events such as the merging of two neutron stars to make them."

According to Space.com, neutron stars - about 1.5 times the mass of the Sun - often form when giant stars die in a supernova. It leaves behind a core so dense that a single teaspoon would weigh a billion tons. When two neutron stars combine, this violent phenomenon creates a supermassive black hole in their own unique explosive force. Researchers are now suggesting that it's a merging of these super-dense cosmic bodies that is responsible for the far-flung dust seen on the ocean floor.

Regardless, the fact that this study showed plutonium existed on Earth at all, and that materials like uranium and thorium are still present, tells scientists that some sort of stellar explosion, supernovae or not, took place - likely when the Earth was just starting to form.

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