- 3749 - SUPERNOVAE - close to us? How dangerous are nearby Supernovae to life on Earth? From a distance, supernovae explosions are fascinating. A star more massive than our Sun runs out of hydrogen and becomes unstable. It explodes and releases so much energy it can outshine its host galaxy for months.
--------------------- 3749 - SUPERNOVAE - close to us?
- Space is vast and largely empty, and supernovae are relatively rare. And most planets don’t support life, so most supernovae probably explode without affecting living things. However, one type of supernova has a more extended reach than thought. And it could have consequences for planets like ours.
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- One supernova hasn’t been close enough to sterilize Earth, but there’s evidence showing supernovae have affected life on Earth. A 2018 paper presented evidence of a supernova exploding near Earth about 2.6 million years ago. It was about 160 light-years away.
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- The evidence tied the supernova to the “Pliocene marine megafauna extinction“. In that event, up to a third of Earth’s large marine species were wiped out, in shallow coastal waters.
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- Another paper showed up to 20 supernovae in the last 11 million years. Some of these were as close as 130 light-years to Earth. About 2 million years ago, one of the supernovae exploded close enough to our planet to damage the ozone layer.
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- But there are different types of supernovae. Some of them have a much longer reach and much greater duration. Scientists have long known about the powerful gamma rays that supernova release during the explosion. They also know about the cosmic rays that can arrive hundreds or thousands of years later. If this happens close enough to a planet like Earth, the cosmic rays can deplete the ozone layer and increase “muon radiation” at the surface.
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- A “type IIn x-ray luminous supernova” is different from other supernovae. When a supernova explodes, it emits gamma rays and other photons immediately. In an x-ray luminous supernova, gamma rays and photons are emitted, but some of the radiation from the explosion interacts with a dense circumstellar medium surrounding the progenitor star. This creates x-rays that can be lethal up to 160 light-years away.
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- In a scenario where an supernova exploded close to Earth, it can take months or years following the initial explosion for the x-rays to arrive. Interactions with the circumstellar debris cause a delay. The x-rays can deplete Earth’s ozone layer, allowing harmful UV radiation from the Sun to reach the planet’s surface. After the x-rays arrive, the cosmic rays arrive.
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- Researchers aren’t sure about the lethal distances of supernovae. There are many variables, both in the progenitor star and its environment. The progenitor star’s mass loss is especially important.
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- SN 1987A supernova exploded in the Large Magellanic Cloud, and the light reached Earth in 1987. Scientists observed the explosion and confirmed the source of energy for the supernova’s visible light. It proved that the long-duration glow after an supernova explosion is radioactive.
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- SN1987A wasn’t lethal, according. The supernova was only deadly to a distance of less than one light-year. It was the least dangerous supernova out of the 31 the team characterized.
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- The most lethal of the 31 was “SN2006jd“. It exploded in the galaxy “NGC 4179“, about 57 million light-years away, and the light reached Earth in 2006. It was lethal out to almost 100 light-years.
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- The five most lethal supernovae in this study are all Type IIn supernovae, as are seven of the top ten. Type IIn supernovae have the greatest range of influence. These supernovae could significantly influence Earth’s biosphere from greater distances.
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- Our Solar System is inside what’s known as the “Local Bubble“. It’s a cavity carved out of the ISM in the Milky Way’s Orion Arm. Multiple supernovae explosions created the bubble in the last 10 to 20 million years.
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- Advances in x-ray astronomy will shed more light on the consequences for terrestrial planets. The interacting X-ray phase of an supernova’s can entail significant consequences for terrestrial planets.
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- Scientists know that supernovae have had some effect on Earth. The presence of the radioactive isotope 60Fe has a half-life of 2.6 million years, yet researchers found undecayed 60Fe in ocean samples dating from 2 to 3 Myr ago. It should’ve decayed into nickel long ago. Supernovae can create 60Fe through nucleosynthesis when they explode.
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- But other things can create 60Fe. Researchers also found 53Mn in the same samples of ferromanganese crust that hold the 60Fe. It’s also a radioactive isotope that should’ve decayed by now. Unlike 60Fe, only supernovae can create 53Mn. Its presence is definite proof of nearby supernovae in the recent geological past.
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- Ionizing radiation from supernovae can alter Earth’s atmospheric chemistry from substantial distances. The initial burst of energy from an supernova poses one threat, and so do the cosmic rays that arrive hundreds or thousands of years later and linger.
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- Another threat is the x-rays that arrive months or years after the initial outburst. Supernovae X-ray emission has had a notable impact on Earth and potentially played a role in the evolution of life itself. Supernova outbursts have almost certainly struck our planet. If the radiation weakened the ozone layer, allowing more UV radiation to reach the Earth’s surface, it would’ve caused mutations. It’s called ”UV mutagenesisz“, which may have driven molecular evolution and been critical in the origin of sex. In fact, mutation is evolution’s primary driver.
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- This research has implications for habitability throughout the galaxy, too. The Galactic Habitable Zone (GHZ) is a region in a galaxy where habitability is most likely. Since supernovae can be fatal for life if close enough, regions with many stars that can potentially explode as supernovae are less habitable.
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- Something huge lurks in the shadows of the Universe. Known as the “Great Attractor“, it is causing the Milky Way and all the surrounding galaxies to rush towards it. We would normally have a better understanding of this situation, except for the fact that the Great Attractor happens to lie in the direction behind the galactic bulge, which makes it difficult for us to observe.
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- A new infrared survey of the region behind the bulge, and they have found yet another large galaxy cluster. Their work is helping to paint a more complete portrait of the environment of the Great Attractor.
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- All galaxies in the Universe are in motion. At the very largest scales this motion is dominated by what astronomers call the “Hubble flow“, which is just the general expansion of the Universe. This causes most galaxies to recede away from each other. But at anything less than fully cosmological scales, there can be extra motion on top of that. For example, the Milky Way and the Andromeda galaxies are on a collision course, and they will merge together in about 5 billion years.
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- In addition to that merger, our two galaxies, along with all the other galaxies in our local group, are rushing towards the Virgo cluster, which is the nearest cluster of galaxies to us.
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- This local group of galaxies, the Virgo cluster, and all the other groups and clusters in the nearby region of space are headed in one direction together. Astronomers call the center point of this movement the “Great Attractor“, because it seems to be the largest source of gravity in our local cosmological environment.
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- The Great Attractor sits in the direction of our sky behind the galactic bulge. This region of the sky is called the Zone of Avoidance, because it’s very difficult for optical telescopes to pierce the thick clouds of dust and gas in this region to develop a clear map of what’s behind it.
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- Astronomers only hope is to use other wavelengths of light that can penetrate gas and dust more easily. One of those wavelengths is “infrared“. But infrared surveys in this regime is a very difficult task, and so our maps in this region of the universe are incomplete.
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- The team of astronomers have attempted a new survey of the region with the Gemini South Telescope, especially targeting a half dozen galaxies within the Zone of Avoidance. They found that the galaxies in their survey were likely to be associated with each other. It’s the first evidence we have that these galaxies might be a member of a much larger cluster of galaxies.
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- This cluster of galaxies isn’t the Great Attractor itself, but it is certainly associated with it. Further observations will hopefully paint a more thorough picture of this new galaxy cluster and its environments, and determine its relationship to the Great Attractor.
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November 22, 2022 SUPERNOVAE - close to us? 3749
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