Jumat, 28 Agustus 2020

We Found A Supernova Under The Sea, Say Scientists - Forbes

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For the last 33,000 years Earth has been travelling through a cloud of faintly radioactive dust from supernovae explosions—and the evidence is in our planet’s oceans, according to a new paper.

Researchers at the The Australian National University’s (ANU) Heavy Ion Accelerator Facility (HIAF) found traces of iron-60 in deep-sea sediments from two different locations that date back 33,000 years.

“These clouds could be remnants of previous supernova explosions, a powerful and super bright explosion of a star,” said lead author Professor Anton Wallner, a nuclear physicist at ANU.

The discovery could shed some light on what’s surrounding the Solar System—but it also asks some tanatalizing questions.

Let’s take a deep-dive.

What is iron-60?

It’s evidence of a supernova—or supernovae because the isotope iron-60 is only formed when stars die in supernova explosions. It has four more neutrons than Earth’s most common form of the element.

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It must have arrived on Earth from beyond the Solar System.

An iron isotope with a half-life of 2.6 million years, iron-60 is radioactive and decays away within 15 million years. Since Earth is 4.6 billion years old, that means any iron-60 found on Earth must have arrived here via supernovae before ending-up in the bottom of our oceans.

The researchers had previously found traces of iron-60 at about 2.6 million years ago, and possibly another at around 6 million years ago.

That suggests that Earth has travelled through multiple clouds of “fallout” from nearby supernovae.

What is a supernova?

An exploding star. At the end of a supergiant star’s life cycle, a star runs out of fuel, the pressure drops, and it collapses so fast that the outer part of the star explodes causing a massive, luminous event that can be briefly brighter than entire galaxies.

Such a supernovae explosion is the source of heavy elements in the Universe, and they leave supernovae remnants—like the Crab Nebula and the Cassiopeia A.

When scientist Carl Sagan said “we are all made of star-stuff,” he was referring to the  carbon, nitrogen and oxygen created in stars and the heavy elements in the remnants of dead stars. It’s less romantic-sounding, but what Sagan could have said—and perhaps more accurately—is that “we’re all made of nuclear waste.”

The culprit, say the researchers, could be the local interstellar cloud (LIC), also known as the “local fluff,” whose make-up and origins are unclear.

What is the ‘local fluff?’

It’s 30 light-years-wide dust clouds that the Solar System is currently moving through and, in fact, has almost departed from. It’s space that has a slightly higher density of hydrogen gas, the most abundant molecule in the Universe.

Earth has probably picked-up particles of iron-60 from this radioactive stardust “fluff” while traveling through it.

Last year researchers in Antarctica discovered similar “stardust” containing iron-60.

However, what this new research hints at is that there’s evidence of iron-60 further back than the Solar System’s journey through the “local fluff.”

That begs two questions:

  • If the “local fluff” cloud was not formed by a supernova, where did it come from?
  • Is iron-60, in fact, evenly spread throughout space?

“There are recent papers that suggest iron-60 trapped in dust particles might bounce around in the interstellar medium,” said Professor Wallner. “So the iron-60 could originate from even older supernovae explosions, and what we measure is some kind of echo.”

Wishing you clear skies and wide eyes.

The Link Lonk


August 28, 2020 at 09:00AM
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We Found A Supernova Under The Sea, Say Scientists - Forbes

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