Ravenous Supermassive Black Holes May Sterilize Nearby Planets

May 30, 2017

By Shannon Hall

The center of any galaxy is a hazardous home. There, supernovae explosions shower nearby planets with x-rays, gamma rays and ultraviolet photons that obliterate any ozone layer present. Gamma-ray bursts hurtle even more damaging shock waves, blasting any biosphere into oblivion. Even encounters with nearby stars knock planets around, driving them out of their habitable zones. “We don’t expect life to be easy within the inner kiloparsec of the Milky Way,” says Abraham Loeb from the Harvard–Smithsonian Center for Astrophysics. But now we can add one more menace to the list that tops the rest: supermassive black holes.

Every large galaxy’s center hosts a supermassive black hole that is wont to throw wild tantrums in its youth. Although many astronomers have speculated these behemoths, called quasars when they are active, would likely wreak havoc on any nearby planets, no one had taken a quantitative look at those effects—until now. A new study, posted on the preprint server arXiv and submitted to Monthly Notices of the Royal Astronomical Society, provides the first calculations that show when, where and how planets are harmed by quasars. And the quota alone is surprisingly high. Loeb and his postdoctoral researcher, John Forbes, found half the planets throughout the universe have lost the equivalent of Mars’s atmosphere, 10 percent have lost the equivalent of Earth’s atmosphere and 0.2 percent have lost the equivalent of Earth’s oceans—all thanks to quasars alone.

Although quasars are known to drive strong winds and jets of relativistic particles that can be dangerous in their own right, Forbes and Loeb looked at the damage caused by their light alone. The accretion disk of debris that orbits the black holes, funneling gas and dust in, are so bright they can outshine all the stars in their galaxies, which are 100,000 times larger. And when that light illuminates the atmosphere of a planet, the high-energy photons transfer energy to those atmospheric particles, giving them the boost to escape the planet’s gravitational pull altogether. Outside experts like Duncan Forgan from the University of Saint Andrews in Scotland are quick to point out the amount of loss depends greatly on the atmosphere’s composition and the planet’s mass. This finding is one piece in a several-million-piece, three-dimensional puzzle, he says, but nonetheless it is still that crucial first piece.

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7 comments on “Ravenous Supermassive Black Holes May Sterilize Nearby Planets

  • The popular media often churn out wishful statistics about “Earth-Type Planets” when the mean “Earth size planets”!
    They become more fanciful when quoting the numbers of stars and likely numbers of habitable planets around those stars!
    The Earth with its large moon is a rare place, in a habitable zone of our Solar-System, in a habitable zone of out galaxy!

    https://phys.org/news/2016-09-galaxy-habitable-zone.html

    The Milky Way is a big place, measuring up to 180,000 light years across. It contains 100 to 400 billion stars spread across this enormous volume.

    We’re located about 27,000 light years away from the center of the Milky Way, and tens of thousands of light-years away from the outer rim.

    The Milky Way has some really uninhabitable zones.
    Down near the center of the galaxy, the density of stars is much greater. And these stars are blasting out a combined radiation that would make it much more unlikely for life to evolve.

    Radiation is bad for life. But it gets worse.
    There’s a huge cloud of comets around the Sun known as the Oort Cloud. Some of the greatest catastrophes in history happened when these comets were kicked into a collision course with the Earth by a passing star.
    Closer to the galactic core, these disruptions would happen much more often.

    There’s another dangerous place you don’t want to be: the galaxy’s spiral arms.
    These are regions of increased density in the galaxy, where star formation is much more common. And newly forming stars blast out dangerous radiation.

    Fortunately, we’re far away from the spiral arms, and we orbit the center of the Milky Way in a nice circular orbit, which means we don’t cross these spiral arms very often.

    We stay nice and far away from the dangerous parts of the Milky Way, however, we’re still close enough to the action that our solar system gathered the elements we needed for life.

    The first stars in the universe only had hydrogen, helium and a few other trace elements left over from the Big Bang. But when the largest stars detonated as supernovae, they seeded the surrounding regions with heavier elements like oxygen, carbon, even iron and gold.

    Our solar nebula was seeded with the heavy elements from many generations of stars, giving us all the raw materials to help set evolution in motion.

    If the solar system was further out, we probably wouldn’t have gotten enough of those heavier elements. So, thanks multiple generations of dead stars.

    According to astrobiologists the galactic habitable zone probably starts just outside the galactic bulge – about 13,000 light-years from the center, and ends about halfway out in the disk, 33,000 light-years from the center.
    Remember, we’re 27,000 light-years from the center, so just inside that outer edge. Phew.

    Of course, not all astronomers believe in this Rare Earth hypothesis.
    In fact, just as we’re finding life on Earth wherever we find water, they believe that life is more robust and resilient. It could still survive and even thrive with more radiation, and less heavier elements.

    Furthermore, we’re learning that solar systems might be able to migrate a significant distance from where they formed. Stars that started closer in where there were plenty of heavier elements might have drifted outward to the safer, calmer galactic suburbs, giving life a better chance at getting a foothold.
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  • Olgun #2
    May 30, 2017 at 4:14 pm

    Scaly-foot_gastropod

    The extra-terrestrial habitable niche issue for extremophiles, is not so much the extreme environment, as the length of duration of their environment, within their tolerable range.

    For abiogenesis from organic chemicals to an organism geared-up and adapted to cope with extreme conditions, that is millions or billions of years.

    For survival of a pre-evolved life-form arriving from elsewhere, the time the window of habitable conditions persists for, could be much shorter – especially if it had the capability to lie dormant for a long time, or move on when conditions deteriorated.
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  • I understand I was working on the edge of probability Alan but say, under the frozen crust of a planets moon where volcanic activity occurs, a perfect contained situation perhaps?
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  • Olgun #4
    Jun 1, 2017 at 7:57 am

    I understand I was working on the edge of probability Alan but say, under the frozen crust of a planets moon where volcanic activity occurs, a perfect contained situation perhaps?

    Where there are niche conditions outside of the main habitable zone of a solar-system, the key question is the stability and the length of time the conditions endure.

    https://www.nasa.gov/content/goddard/long-stressed-europa-likely-off-kilter-at-one-time

    By analyzing the distinctive cracks lining the icy face of Europa, NASA scientists found evidence that this moon of Jupiter likely spun around a tilted axis at some point.

    This tilt could influence calculations of how much of Europa’s history is recorded in its frozen shell, how much heat is generated by tides in its ocean, and even how long the ocean has been liquid.

    Where tides are generated from a planet or moon’s spin, with the rotational inertia representing a finite quantity of energy, this will eventually run out.

    If a moon of a giant planet is a captured body which was held in orbit after approaching close, the question arises, “How long ago was it captured”? – and “How long will it remain in that orbit”?

    If moons formed from a proto-satellite disk (a bit like a thicker version of Saturn’s rings) the early ones are likely to spiralled down and fallen into the planet.

    https://en.wikipedia.org/wiki/Galilean_moons#Origin_and_evolution

    Jupiter’s regular satellites are believed to have formed from a circumplanetary disk, a ring of accreting gas and solid debris analogous to a protoplanetary disk.[49][50] They may be the remnants of a score of Galilean-mass satellites that formed early in Jupiter’s history.[15][49]

    Simulations suggest that, while the disk had a relatively high mass at any given moment, over time a substantial fraction (several tenths of a percent) of the mass of Jupiter captured from the Solar nebula was processed through it.
    However, the disk mass of only 2% that of Jupiter is required to explain the existing satellites.[49] Thus there may have been several generations of Galilean-mass satellites in Jupiter’s early history.
    Each generation of moons would have spiraled into Jupiter, due to drag from the disk, with new moons then forming from the new debris captured from the Solar nebula.[49]
    By the time the present (possibly fifth) generation formed, the disk had thinned out to the point that it no longer greatly interfered with the moons’ orbits.[15]
    The current Galilean moons were still affected, falling into and being partially protected by an orbital resonance which still exists for Io, Europa, and Ganymede. Ganymede’s larger mass means that it would have migrated inward at a faster rate than Europa or Io.

    The debris disk has thinned out and Europa is locked into its orbit by orbital resonance with other moons, so its after a late start as a moon of Jupiter, orbit is more stable than it might be otherwise.
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  • Olgun #6
    Jun 1, 2017 at 10:07 am

    With Saturn, they have the moons moving away from it and have calculated down from 4.5 billion years old to a 100 million or less.

    100 million years is definitely a short time for any in-situ abiogenesis and evolution to take place, but could still possibly support some life imported from elsewhere on meteorites from impacts on other planets.

    http://www.bbc.co.uk/earth/story/20150313-the-toughest-animals-on-earth

    http://m.esa.int/Our_Activities/Human_Spaceflight/Research/Tiny_animals_survive_exposure_to_space

    https://www.extremetech.com/extreme/188479-astronauts-find-living-organisms-clinging-to-the-international-space-station-and-arent-sure-how-they-got-there
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