Black Holes Set the Clock for Life on Earth

Black Hole Formation
Black hole formation illustration. (Image credit: ESO/M. Kornmesser)

There is a chance – just a chance – that if black holes rule the universe, they could have "switched on" habitable planets, such as Earth, allowing them to support complex life.

It's an unavoidable implication of the work of astrophysicist Paul Mason, who is examining the role of the super high-energy particles from black holes and exploding stars in the advent of habitable planets.

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Before life started on Earth, the planet was bathed in deadly radiation from the younger, angrier sun as well as a high tide of energetic particles – a.k.a. cosmic rays – being blasted around the galaxy and universe by exploding stars and giant black holes at the centers of galaxies. At some point the cosmic ray flux dropped enough so that life on Earth – and on any Earth-like planet anywhere in the universe – had a chance to flourish.

"It has taken the universe a while for the cosmic ray density and the frequency of bad events to decrease enough for life to handle it," Mason told Discovery News. Mason is a professor at New Mexico State University in Las Cruces and presented his work on Wednesday at the meeting of the American Astronomical Society in Kissimmee, Fla.

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Those bad events include supernovas – the explosive deaths of very large and short-lived stars – which were much more common in the early universe, when the rates of stars births was far higher, said Mason. Other very bad events were the storms of radiation that might have blown from the gigantic central black holes of galaxies when they gulped down matter. Such feeding frenzies – and the harsh, sterilizing radiation they released – were also more common in the past, as astronomers have learned by looking at more distant, and therefore more ancient, galaxies.

Compounding the early universe's problem with life is the fact that everything was much closer together. The small young universe was packed thick with sterilizing cosmic rays. It took billions of years for the expanding universe to pull things apart and help thin that deadly soup.

"It implies that the expansion of the universe is important for life," Mason said, regarding this cosmic ray perspective on the universe.

What also helped life eventually fend off cosmic rays were the leftovers of all those supernovas. Dying stars are element factories which created the oxygen and nitrogen atoms that are now the primary components of our atmosphere. That atmosphere is what protects us from all but the most powerful cosmic rays that are still banging around the galaxy.

Mason's cosmic ray story seems to fit the observable universe, but there are still lots of unanswered questions. For instance, do all giant black holes necessarily zap their galaxies with the most dangerous, highest-energy cosmic rays?

"It's not very well established that these (giant black holes) release very high energy cosmic rays," said physicist Dimitra Atri of the Blue Marble Space Institute of Science in Seattle.

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And there is also the question of just what dose of cosmic rays is actually bad for life.

"If a (cosmic ray) dose is high enough it can kill something," said Atri. "But at the same time it can cause mutations and lead to evolution of many more types of species."

A lethal dose to a human is also not necessarily lethal to other organisms, Atri added. It's even conceivable that there are forms of life – bacteria, for instance – that thrive on cosmic rays and that we might find them within the Earth itself. If so, cosmic rays might not be such a key factor for habitability after all.

"There is a big spectrum for life on Earth," said Atri. "If you look closely at habitability, it is more about water."

As for Earth's chances of being one of the first living planets in the universe, "We don't know is that this means Earth is among the earliest," said Mason. Right now, he said, it's a very interesting matter of speculation.

This article was provided by Discovery News.

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