- 3740 - GAMMA RAY BURSTS - could they destroy us? On October 9, 2022, a beam of light more energetic than astronomers had ever seen zipped past our planet, temporarily blinding detectors on several NASA satellites. The beam came from a gamma-ray burst, the most energetic type of explosion known to occur in the universe, which is believed to accompany the birth of some black holes.
----------------------------- Galaxy in gamma rays
--------------- 3740 - GAMMA RAY BURSTS - could they destroy us?
- Within hours after this gamma-ray burst dozens of telescopes all over the world were pointing in the direction of the burst's source. The event, “GRB221009A“, has since earned the nickname BOAT ("brightest of all time"), and astronomers hope it will help shed light on the mind-boggling physics behind these cataclysmic phenomena.
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- Gamma-ray bursts are not rare. About once a day, one flashes briefly at our planet from somewhere in the universe. Many more are believed to take place throughout the universe. Some gamma-ray bursts light up for just a fraction of a second, probably triggered by collisions of neutron stars, which are stellar corpses left after supernova explosions of massive stars that have run out of fuel in their cores.
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- Other gamma-ray bursts can last for several minutes, most likely caused when a black hole, just born out of a supernova explosion, swallows up so much of its parent star at once that it has to get rid of some in the form of an extremely powerful jet.
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- This particular gamma-ray burst stood out even among the long-firing gamma-ray bursts previously observed, its photons bombarding satellite detectors for about 10 minutes. The energy those photons packed was higher than any that had been measured before. At 18 tera-electronvolts, some the photons outperformed by at least a factor of two the most energetic particles produced by Earth's most powerful particle generator, the Large Hadron Collider.
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- The burst's afterglow, caused by the interaction of gamma-rays with cosmic dust, was out of the ordinary as well, outshining any other seen before despite the fact that this burst emanated from a part of the sky obstructed by the thick band of the Milky Way galaxy. The burst was so powerful that it ionized Earth's atmosphere and disrupted long wave radio communications.
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- Astronomers used the Gemini South telescope in Chile to observe the aftermath of GRB221009A on October 14, 2022, nearly a week after it first lit up. Astronomers did find the source: a dust-filled galaxy in the constellation ‘Sagitta‘, also known as “the Arrow“.
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- These gamma-ray bursts come from the collapse of massive stars, and these stars have very short lifetimes. They follow the star formation history of the universe. So where star formation peaks, these long gamma-ray bursts peak, which is at about half the age of the universe. The source of GRB221009A lies about 2.4 billion light-years from Earth. At least 50 telescopes are looking at it in all wavelengths.
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- Although only they are lasting for a few short minutes, gamma-ray bursts trigger effects that can be observed for weeks. Astronomers also look for the supernova explosion that generated the burst, which expels material outward more slowly.
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- Our current understanding of these explosions is that you have a massive star and as it implodes, it creates a black hole, which then some of the material from the star falls into it. The black hole then spits it out as a jet, which is moving nearly at the speed of light, the “gamma-ray burst“. At the same time, when the star implodes, some of that material rebounds outwards, essentially begins moving away at much slower speeds. And this is the “supernova explosion“.
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- As the gamma-rays of the initial burst interact with material in the surrounding universe, they produce an afterglow, which spans the electromagnetic spectrum but is best observed in X-ray and radio wavelengths.
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- Astronomers hope to learn how much mass was created in that event. They hope to learn what chemical elements were created . We still don't know how some of the heaviest elements in the universe have been created, and we think that we might be able to see such processes in supernova explosions.
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- Gamma ray bursts were first discovered by accident in the 1960s by U.S. military satellites developed to keep an eye on Soviet nuclear testing (which, too, produces gamma-rays). Gamma-ray bursts remained a complete mystery for decades. It was only in the 1990s that astronomers first realized that these powerful flashes of light coming from all corners of the universe might have something to do with collapsing giant stars.
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- While the relative proximity of a burst as powerful as GRB221009A is a boon to science, astronomers are not keen to see a gamma-ray burst much closer to Earth. Especially not in our galaxy. Scientists think that a gamma-ray burst aimed at our planet from a distance of some thousands of light-years would destroy the planet's protective ozone layers and trigger changes in the atmosphere that might lead to an ice age.
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- In fact, one such gamma-ray burst may have triggered one of the five major extinction events in Earth's history, the “Ordovician mass extinction” some 440 million years ago.
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- The jets that cause the gamma-ray bursts are very narrowly beamed. Only a few degrees wide. But if it were to happen in our galaxy and was pointed at us, it would be really dangerous to us. Luckily, the rate of these events that we expect to happen in every galaxy is incredibly low.
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- From a distance, supernovae explosions are fascinating too. A star more massive than our Sun runs out of hydrogen and becomes unstable. Eventually, it explodes and releases so much energy it can outshine its host galaxy for months. But space is vast and largely empty, and supernovae are relatively rare.
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- Most planets don’t support life, so most supernovae probably explode without affecting living things. A new study shows how one type of supernova has a more extended reach than thought. And it could have consequences for planets like ours.
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- Earth is no stranger to supernovae. One 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. The supernova was tied to the Pliocene marine megafauna extinction. In that event, up to a third of Earth’s large marine species were wiped out, but only in shallow coastal waters.
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- Another paper showed up to 20 supernovae in the last 11 million years in the Scorpius-Centaurus OB association. 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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- 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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- 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.
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- After the x-rays arrive, the cosmic rays arrive. This is a double whammy for Earth’s ozone layer.
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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. But by characterizing the lethal x-ray dose for Earth’s stratosphere and the energy output of some of the brightest supernovae.
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- SN 1987A 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 SN’s visible light for the first time. It proved that the long-duration glow after an SN explosion is radioactive.
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- “SN1987A” wasn’t very lethal. They say the SN was only deadly to a distance of less than one light-year. It was the least dangerous SN out of the 31 the team characterized. 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. According to the researchers, SN2006jd was lethal to almost 100 light-years.
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- The five most lethal SNs in this study are all Type IIn supernovae, as are seven of the top ten.
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- Our Solar System is inside what’s known as the “Local Bubble“. It’s a cavity carved out of the space in the Milky Way’s Orion Arm. Multiple supernovae explosions created the bubble in the last 10 to 20 million years. Did those SN affect Earth?
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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. “Asymptomatic giant branch stars” can make it, too, so by itself, it’s not a smoking gun for a nearby supernova.
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- 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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- It’s not the presence of these radioactive isotopes that poses a threat to life. It’s the radiation that must’ve struck Earth, and if the supernova that created the isotopes was close enough to spread them to Earth, then the radiation must’ve struck Earth, too.
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- Ionizing radiation from supernovae can alter Earth’s atmospheric chemistry from substantial distances. The initial burst of energy from an SN poses one threat, and so do the cosmic rays that arrive hundreds or thousands of years later and linger. But this research adds another threat: x-rays that arrive months or years after the initial outburst. “Therefore, a corollary of the formidable threat found here is that this alters the timeline by which we know an SN can influence a nearby planet, adding an additional phase of adverse effects.”
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- Exactly what effect did it have? Combining these findings with our threat assessment here, it is possible that one or more of these SNe were interacting, and thus inflicted a high dosage of X-ray radiation on Earth’s atmosphere. This would imply that SN X-ray emission has had a notable impact on Earth and potentially played a role in the evolution of life itself.
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- SN outbursts have almost certainly struck our planet. The exact consequences are difficult for scientists to untangle. But 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 mutagenesis“, 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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- We thus conclude that further research into SN X-ray emission has value not just for stellar astrophysics but also for astrobiology, paleontology, and the Earth and planetary sciences as a whole.
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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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- Supernovae can be lethal at greater distances than thought and can be fatal in the period of a few months or years after the initial outburst due to the x-rays. That alters the shape and location of a galaxy’s GHZ.
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- November 12, 2022 GAMMA RAY BURSTS - could they destroy us? 3740
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