How likely and severe is the threat of a gamma ray burst to earth?

How likely and severe is the threat of a gamma ray burst to earth?

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In the National Geographic article: it is suggested that a gamma ray burst likely caused a mass extinction in earth's history. How severe is the threat of a gamma ray burst to life on earth? It would be nice to see a chart that considers the threat within the next hundred years as follows (I have no idea what the actual numbers are, hence I am asking):

Severity - Likelihood in 100 years:

  • Global extinction - 0.0000001%
  • Major impact - 0.001%
  • Moderate impact - 0.1%
  • Minor impact (e.g. deplete ozone layer by 0.01%) - 10%
  • Observable - 100% ("minor" gamma ray bursts are frequently detected)

Follow up questions are:

  • Would there be any warning of an impending severe gamma ray burst?
  • Could we survive in gamma ray burst shelters? (it would appear being underground may be sufficient according to: and

Something else I found to be shocking is that the Bible appears to predict such an event. I would rate the predicted event on the major impact level. I asked about this in the Christian This Site here:

I'll address WR104 first. The National Geographic article calls it a "potential threat." Yet that potential may be low. There are a slew of articles quoting astronomer Grant Hill on the subject. Hill studied the star and found that it looks like it isn't pointing straight at us. Its axis might be up to 45 degrees in another direction, meaning that we'd be fine if it underwent a burst.

From here:

It would appear the original Keck imagry may not have been as straight-forward as it seemed. Spectroscopic emission lines from the binary pair strongly suggest the system is in fact inclined 30°-40° (possibly as much as 45°) away from us.

So, Earth doesn't appear to be in the firing line of WR 104 after all…

Here and here Hill is quoted as saying that the star looks like it could be pointed at us - which goes against the evidence he found! Finally, this is another example of Hill's cautious attitude: The evidence says we're good, but he's not making any assumptions.

Sabre Tooth, I know you said that you didn't want Wikipedia, but my primary goal here isn't to collect the bounty, so I'm going to reference it in this section. I hope you're okay with that. I may withdraw it, though, if Jonathan indicates that he doesn't want it.

Okay, back to the topic at hand. Wikipedia, of course, has a short tidbit on the frequency of gamma-ray bursts effecting Earth:

Estimating the exact rate at which GRBs occur is difficult, but for a galaxy of approximately the same size as the Milky Way, the expected rate (for long-duration GRBs) is about one burst every 100,000 to 1,000,000 years. Only a small percentage of these would be beamed towards Earth. Estimates of rate of occurrence of short-duration GRBs are even more uncertain because of the unknown degree of collimation, but are probably comparable.

'A small percentage' isn't too specific. The BBC article that is cited in this passage says the following:

Observations of deep space suggest that gamma ray-bursts are rare. They are thought to happen at the most every 10,000 years per galaxy, and at the least every million years per galaxy.

However, the 'small percentage' is never elaborated on.

That's all I have for this edit; more to come later. By the way, this Physics.SE question may interest anyone reading this…

Astrophysical and Cosmological Constraints on Life

Paul A. Mason , Peter L. Biermann , in Habitability of the Universe Before Earth , 2018

3.2 Gamma-Ray Bursts (GRBs)

GRBs are stellar explosions that generate enormous radiation beamed in two opposing directions. Local GRBs may occasionally sterilize large portions of the land-based life in the Galaxy. Annis (1999 ) argues that GRBs are so critical to astrobiology that the Universe is currently undergoing a phase transition from no intelligent life to intelligence as a result of the reduction of GRBs. While we generally agree that the reduction in number and luminosity of GRBs is critical to habitability, the timing of this transition is likely not universal. Galaxies with active SMBHs, especially those resulting from mergers, will remain uninhabitable for many Gyr into the future.

Notwithstanding atmospheric removal by a close and beamed GRB, the greatest impact of GRBs on surface or shallow marine life is the depletion of ozone and the subsequent exposure to stellar ultraviolet radiation. Melott et al. (2005 ) pointed out that DNA damage in organisms on Earth from GRBs is greatest at mid latitudes due to local ozone depletion due to enhanced ultraviolet B-band (UVB) radiation and the direct angle of GRB at these latitudes. Hence, in most cases (except the worst scenarios) GRBs would result in a mass extinction over large surface areas but not planetary sterilization. Galante and Horvath (2007 ) also examined the astrobiological impacts of direct GRBs and found that at distances up to 100 kpc there may be significant ozone depletion and thus more stellar UVB reaching the ground. Compounding the situation there would be less 350–450 nm stellar radiation reaching the ground resulting in a less efficient photo-repair of DNA damage. Also, the reduction of visible light, also known as photosynthetically active radiation (PAR), would slow down photosynthesis.

Direct CR flux from GRBs would be sterilizing only for a very close GRB source, less than about 10 pc. Since the integrated radiation is what drives their impact, GRBs are too brief to do extensive damage, unless they are quite close and/or if they are beamed directly at the planet. Using determinations of the luminosity functions and the rates of GRBs with consideration of host galaxy properties, Piran and Jimenez (2014) estimated the probability of a lethal GRB within a galaxy, which appeared to be much greater in the inner Milky Way, than locally. Specifically, that GRBs have a 95% probability of sterilizing a planet within 4 kpc of the galactic center. They further suggested that planets further out in the Galaxy play a game of “GRB Roulette” as the probability of mass extinction by GRB decreases to 50% beyond 10 kpc. Their work also suggests that the Earth, at the distance of 8 kpc from the Galactic center, has likely been exposed to one sterilizing GRB event.

There is an indication that at least one Galactic GRB has occurred in the last million years or so. The argument is as follows. The highest energy particles accelerated from a GRB are mostly neutrons. Protons remain trapped in the magnetic field and thus lose energy adiabatically during escape. A relativistic neutron travels through the Galactic disk and decays after some time into a proton, an electron, and an antineutrino. The proton is then caught by the Galactic magnetic field and with a small probability (about 0.05) interacts with the interstellar medium, again becoming a neutron traveling to us undeflected. Biermann et al. (2004 ) estimated that one to a few GRBs occurring about a million years ago within 3 kpc of the Galactic center can account for the excess of EV CRs by this process, detected by one instrument, AGASA- the Akeno Giant Air Shower Array (Hayashida et al., 1999 Teshima et al., 2001) , but not confirmed by IceTop - the surface array of the IceCube neutrino telescope ( Aartsen et al., 2016 ).

Are gamma ray bursts dangerous?

A new research paper reveals more details of the effect gamma ray bursts (GRB) have had on the development of complex life throughout the cosmos. Illustration depicts a beam from a GRB as might have been directed toward early life on Earth during the Cambrian or Ordovician periods,

500 million years ago. Credit: T. Reyes

If comics have taught me anything, it's that gamma powered superheroes and villains are some of the most formidable around.

Coincidentally, Gamma Ray bursts, astronomers say, are the most powerful explosions in the Universe. In a split second, a star with many times the mass of our Sun collapses into a black hole, and its outer layers are ejected away from the core. Twin beams blast out of the star. They're so bright we can see them for billions of light-years away. In a split second, a gamma ray burst can release more energy than the Sun will emit in its entire lifetime. It's a super-supernova.

You're thinking "Heck, if the gamma exposure worked for Banner, surely a super-supernova will make me even more powerful than the Hulk." That's not exactly how this plays out.

For any world caught within the death beam from a gamma ray burst, the effects are devastating. One side of the world is blasted with lethal levels of radiation. Our ozone layer would be depleted, or completely stripped away, and any life on that world would experience an extinction level event on the scale of the asteroid that wiped out the dinosaurs.

Astronomers believe that gamma ray bursts might explain some of the mass extinctions that happened on Earth. The most devastating was probably one that occurred 450 million years ago causing the Ordovician–Silurian extinction event. Creatures that lived near the surface of the ocean were hit much harder than deep sea animals, and this evidence matches what would happen from a powerful gamma ray burst event. Considering that, are we in danger from a gamma ray burst and why didn't we get at least one Tyrannosaurus Hulk out of the deal?

There's no question gamma ray bursts are terrifying. In fact, astronomers predict that the lethal destruction from a gamma ray burst would stretch for thousands of light years. So if a gamma ray burst went off within about 5000-8000 light years, we'd be in a world of trouble.

Astronomers figure that gamma ray bursts happen about once every few hundred thousand years in a galaxy the size of the Milky Way. And although they can be devastating, you actually need to be pretty close to be affected. It has been calculated that every 5 million years or so, a gamma ray burst goes off close enough to affect life on Earth. In other words, there have been around 1,000 events since the Earth formed 4.6 billion years ago. So the odds of a nearby gamma ray burst aren't zero, but they're low enough that you really don't have to worry about them. Unless you're planning on living about 5 million years in some kind of gamma powered superbody.

We might have evidence of a recent gamma ray burst that struck the Earth around the year 774. Tree rings from that year contain about 20 times the level of carbon-14 than normal. One theory is that a gamma ray burst from a star located within 13,000 light-years of Earth struck the planet 1,200 years ago, generating all that carbon-14.

This artist’s impression of a gamma-ray burst shows the two intense beams of relativistic matter emitted by the black hole. To be visible from Earth, the beams must be pointing directly towards us. Credit: NASA/Swift/Mary Pat Hrybyk-Keith and John Jones

Clearly humanity survived without incident, but it shows that even if you're halfway across the galaxy, a gamma ray burst can reach out and affect you. So don't worry. The chances of a gamma ray burst hitting Earth are minimal. In fact, astronomers have observed all the nearby gamma ray burst candidates, and none seem to be close enough or oriented to point their death beams at our planet. You'll need to worry about your exercise and diet after all.

So what do you think? What existential crisis makes you most concerned, and how do gamma ray bursts compare?

Earth May Still Lie In Path Of Potential Gamma-Ray Burst (GRB), Say Astronomers

Fifteen years after its discovery, two astronomers say earth may still lie within the sights of a potentially lethal progenitor of a stellar gamma-ray burst (GRB).

Although WR 104, a Wolf-Rayet star some 8000 light years distant, has thus far remained largely quiescent, it is ripe to undergo a core-collapse supernova of the sort that could generate a seconds-long burst of gamma-rays that, in turn, might potentially wipe out a quarter of earth’s protective atmospheric ozone.

“We could see it go supernova anywhere from tomorrow to 500,000 years from now,” said Grant Hill, an astronomer at the W.M. Keck Observatory in Hawaii. “For all intents and purposes, the gamma-ray burst and optical photons from the supernova would arrive simultaneously.”

The question of whether a GRB from WR 104 --- which lies in the direction of our Milky Way’s galactic center --- would actually cross earth’s path has been the subject of debate for years now. But Grant says that given the continuing uncertainty about the star’s alignment with our own, such a scenario can’t be ruled out.

Discussion, heretofore, has centered on conflicting measurements of the star’s rotational axis and whether WR 104’s polar orientation lies “face on” to earth’s line of sight or whether it is inclined by as much as 30 to 40 degrees.

If the star lies “pole on” to earth that would mean that we would be directly in the line of fire of such a burst which might travel along a beam as large as 20-degrees in diameter. If indeed, the star’s polar inclination to earth is 30 degrees, then earth would be untouched.

However, Peter Tuthill, an astronomer at the University of Sydney in Australia, and colleagues, first found WR 104 in 1998 via an advanced method of ground-based infrared imaging while observing with the Keck I telescope. They found that the star’s orbital inclination to earth appeared to be 10 to 15 degrees. Even so, Hill’s own optical spectroscopic measurements using the Keck I several years later, found the inclination to be 30 to 40 degrees.

“But if you look at WR 104 and the image of its pinwheel,” said Hill, “it really is a visceral and powerful argument that the thing is face on with an inclination of zero.”

Wolf-Rayet stars are highly-evolved, very luminous massive stars that have been stripped of their outer hydrogen envelopes through extreme mass loss.

When such stars are found in a binary system such as WR 104, then dense high-velocity colliding stellar winds from the two stars sometimes leads to significant dust formation. In the case of WR 104, these winds have created a spiral pinwheel-like nebula extending out to 160 astronomical units (A.U.) or twice the orbital diameter of Pluto to our sun.

“There are more than a hundred known galactic Wolf-Rayet stars which makes them incredibly rare,” said Tuthill. “Any of these could potentially be a GRB. WR 104 is the only one to appear just face on [or in the plane of the sky].”

Hill says that if WR 104 does go supernova and emits a GRB, the burst would emerge from the star’s two opposite poles.

Dust streaming from the Wolf-Rayet 104 binary star system creates a pinwheel nebula. Credit: U.C. . [+] Berkeley Space Sciences Laboratory, W.M. Keck Observatory

Since announcing his initial WR 104 measurements, Hill says he has refined his computer models. Thus, he expects to get a better handle on the star’s true inclination by reanalyzing his existing data the results of which will be submitted to a refereed astronomical journal within a year.

“It’s a complicated system and either of us might have made an oversimplification,” said Tuthill, who adds that chances still remain remote that the star's core-collapse supernova would automatically generate a follow-on GRB.

But if such a GRB did hit earth’s atmosphere, says Adrian Melott, a physicist at the University of Kansas in Lawrence, it would likely cause a 50 percent increase in solar UVB radiation which would not only disrupt photosynthesis among marine and freshwater plankton, but also likely precipitate some sort of broader extinction event.

“You would first notice a 10-second blue flash in the upper atmosphere,” said Melott, “but then the damage would be done.”

Did Deadly Gamma-Ray Burst Cause a Mass Extinction on Earth?

A gamma-ray burst, the most powerful kind of explosion known in the universe, may have triggered a mass extinction on Earth within the past billion years, researchers say.

These deadly outbursts could help explain the so-called Fermi paradox, the seeming contradiction between the high chance of alien life and the lack of evidence for it, scientists added.

Gamma-ray bursts are brief, intense explosions of high-frequency electromagnetic radiation. These outbursts give off as much energy as the sun during its entire 10-billion-year lifetime in anywhere from milliseconds to minutes. Scientists think gamma-ray bursts may be caused by giant exploding stars known as hypernovas, or by collisions between pairs of dead stars known as neutron stars. [Top 10 Greatest Explosions Ever]

If a gamma-ray burst exploded within the Milky Way, it could wreak extraordinary havoc if it were pointed directly at Earth, even from thousands of light-years away. Although gamma rays would not penetrate Earth's atmosphere well enough to burn the ground, they would chemically damage the atmosphere, depleting the ozone layer that protects the planet from damaging ultraviolet rays that could trigger mass extinctions. It's also possible that gamma-ray bursts may spew out cosmic rays, which are high-energy particles that may create an experience similar to a nuclear explosion for those on the side of the Earth facing the explosion, causing radiation sickness.

To see how great a threat gamma-ray bursts might pose to Earth, researchers investigated how likely it was that such an explosion could have inflicted damage on the planet in the past.

Gamma-ray bursts are traditionally divided into two groups &mdash long and short &mdash depending on whether they last more or less than 2 seconds. Long gamma-ray bursts are associated with the deaths of massive stars, while short gamma-ray bursts are most likely caused by the mergers of neutron stars.

For the most part, long gamma-ray bursts happen in galaxies very different from the Milky Way &mdash dwarf galaxies low in any element heavier than hydrogen and helium. Any long gamma-ray bursts in the Milky Way will likely be confined in regions of the galaxy that are similarly low in any element heavier than hydrogen and helium, the researchers said.

The scientists discovered the chance that a long gamma-ray burst could trigger mass extinctions on Earth was 50 percent in the past 500 million years, 60 percent in the past 1 billion years, and more than 90 percent in the past 5 billion years. For comparison, the solar system is about 4.6 billion years old.

Short gamma-ray bursts happen about five times more often than long ones. However, since these shorter bursts are weaker, the researchers found they had negligible life-threatening effects on Earth. They also calculated that gamma-ray bursts from galaxies outside the Milky Way probably pose no threat to Earth.

These findings suggest that a nearby gamma-ray burst may have caused one of the five greatest mass extinctions on Earth, such as the Ordovician extinction that occurred 440 million years ago. The Ordovician extinction was the earliest of the so-called Big Five extinction events, and is thought by many to be the second largest. [Wipe Out: History's Most Mysterious Extinctions]

The scientists also investigated the danger that gamma-ray bursts may pose for life elsewhere in the Milky Way. Stars are packed more densely together toward the center of the galaxy, meaning worlds there face a greater danger of gamma-ray bursts. Worlds in the region about 6,500 light-years around the Milky Way's core, where 25 percent of the galaxy's stars reside, faced more than a 95 percent chance of a lethal gamma-ray burst within the past billion years. The researchers suggest that life as it is known on Earth could survive with certainty only in the outskirts of the Milky Way, more than 32,600 light-years from the galactic core.

The researchers also explored the danger gamma-ray bursts could pose for the universe as a whole. They suggest that because of gamma-ray bursts, life as it is known on Earth might safely develop in only 10 percent of galaxies. They also suggest that such life could only have developed in the past 5 billion years. Before then, galaxies were smaller in size, and gamma-ray bursts were therefore always close enough to cause mass extinctions to any potentially life-harboring planets.

"This may be an explanation, or at least a partial one, to what is called the Fermi paradox or the 'Big Silence,'" said lead study author Tsvi Piran, a physicist at the Hebrew University in Jerusalem. "Why we haven't encountered advanced civilizations so far? The Milky Way galaxy is much older than the solar system and there was ample time and ample space &mdash the number of planetary systems with conditions similar to Earth is huge &mdash for life to develop elsewhere in the galaxy. So why we haven't encountered advanced civilizations so far?"

The answer to Fermi's paradox may be that gamma-ray bursts have struck many life-harboring planets. The most severe criticism of these estimates "is that we address life as we know it on Earth," Piran told Live Science. "One can imagine very different forms of life that are resilient to the relevant radiation."

Piran and his colleague, Raul Jimenez, detailed their findings online today (Dec. 5) in the journal Physical Review Letters.

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2014 June 3
WR 104: A Pinwheel Star System
Image Credit & Copyright: P. Tuthill (U. Sydney) & J. Monnier (U. Michigan), Keck Obs., ARC, NSF

Explanation: Might this giant pinwheel one-day destroy us? Probably not, but investigation of the unusual star system Wolf-Rayet 104 has turned up an unexpected threat. The unusual pinwheel pattern has been found to be created by energetic winds of gas and dust that are expelled and intertwine as two massive stars orbit each other. One system component is a Wolf-Rayet star, a tumultuous orb in the last stage of evolution before it explodes in a supernova -- an event possible anytime in the next million years. Research into the spiral pattern of the emitted dust, however, indicates the we are looking nearly straight down the spin axis of the system -- possibly the same axis along which a powerful jet would emerge were the supernova accompanied by a gamma-ray burst. Now the WR 104 supernova itself will likely be an impressive but harmless spectacle. Conversely, were Earth really near the center of the powerful GRB beam, even the explosion's 8,000 light year distance might not be far enough to protect us. Currently, neither WR 104 nor GRB beams are understood well enough to know the real level of danger.

Using cosmic-ray neutron bursts to understand gamma-ray bursts from lightning

Analysis of data from a lightning mapper and a small, hand-held radiation detector has unexpectedly shed light on what a gamma-ray burst from lightning might look like -- by observing neutrons generated from soil by very large cosmic-ray showers. The work took place at the High Altitude Water Cherenkov (HAWC) Cosmic Ray Observatory in Mexico.

"This was an accidental discovery," said Greg Bowers, a scientist at Los Alamos National Laboratory and lead author of the study published in Geophysical Research Letters. "We set up this system to study terrestrial gamma-ray flashes -- or gamma-ray bursts from lightning -- that are typically so bright you can see them from space. The idea was that HAWC would be sensitive to the gamma-ray bursts, so we installed a lightning mapper to capture the anatomy of the lightning development and pinpoint the lightning processes producing them."

The team, including Xuan-Min Shao and Brenda Dingus also from Los Alamos, used a small, handheld particle detector, expecting that a terrestrial gamma-ray flash would generate a clear gamma-ray signal in the small particle detector.

"Our system ran for almost two years, and we saw a lot of lightning," said Bowers. But during those storms, they did not observe anything that looked like terrestrial gamma-ray flashes. "We did, however, see large count-rate bursts during clear, fair-weather days, which made us scratch our heads."

HAWC data gathered during these times showed that, in every case, the large array that comprises HAWC had been overwhelmed by extremely large cosmic-ray showers -- so large that the Los Alamos researchers couldn't estimate their size.

UC Santa Cruz collaborator David Smith found that these fair-weather bursts had previously been observed by scientists in Russia, who called them "neutron bursts," and determined that they were the result of neutron production in the soil around the impact point of cosmic ray shower cores.

Previous work that simulated these events had only considered hadrons -- a type of subatomic particle -- in the core of the showers. In addition to hadrons and other particles, cosmic-ray shower cores also contain a lot of gamma rays.

For this work, William Blaine, also of Los Alamos, simulated large cosmic ray-showers, and included both hadrons and gamma rays. "We were able to match our observations with the simulations," said Bowers. "We found that the gamma rays produce the same type of neutron burst as the hadrons."

This study suggests that any natural phenomena that produces a beam of gamma-rays pointed towards the ground (such as downward terrestrial gamma-ray flashes), could produce a similar "neutron burst" signature. This is significant for future terrestrial gamma-ray flash observation modeling efforts.

"It tell us that you can't just model the gamma rays hitting your detector, you'll also have to consider the neutron burst that's happening nearby," said Bowers.

The HAWC Observatory comprises an array of water-filled tanks high on the flanks of the Sierra Negra volcano in Puebla, Mexico, where the thin atmosphere offers better conditions for observing gamma rays. When gamma rays strike molecules in the atmosphere they produce showers of energetic particles. When some of those particles strike the water inside the HAWC detector tanks, they produce flashes of light called Cherenkov radiation. By studying these Cherenkov flashes, researchers reconstruct the sources of the showers to learn about the particles that caused them.

How likely and severe is the threat of a gamma ray burst to earth? - Astronomy

In the Stars: Searching For Armageddons

Swift caps off a 30-year hunt to understand the nature of gamma-ray bursts, flashes of light that burn as brightly as a billion-billion suns.
Washington DC (UPI) Nov 23, 2004
The universe was regarded even until the early 20th century as a stable and eternal place, but evidence collected in the intervening years has shown the cosmos is anything but placid. It is seething with activity, some of it entirely hostile to life.

One piece of that evidence concerns phenomena known as gamma-ray bursts, which are extremely powerful explosions now thought to be detonated by the birth of black holes.

Just as particle accelerators can produce more energy in a microsecond than the electric power the entire country uses in a year, for a brief time, gamma-ray bursts - or GRBs, as astronomers call them - shine more brightly than entire clusters of galaxies.

As powerful as they are, GRBs are elusive. They often last less than 1 second and no longer than a few minutes - a characteristic that has presented a challenge to astronomers wishing to study them.

The problem involves communication and reaction time. Earth-based observers must first communicate to the world's astronomy instruments - telescopes and detectors of every wavelength - that a GRB has been spotted.

Then the instruments must separate from their current objectives and refocus on the appropriate area of the sky. Because the burst disappear so quickly, the process is rarely successful.

So, NASA has launched a nimble spacecraft called Swift that is designed to help capture data about GRBs and their possible relationship to black holes.

Blasting off atop a Boeing Delta II rocket from Cape Canaveral, Fla., last Saturday, Swift is a multi-wavelength observatory - meaning it can watch for GRBs and afterglows in the gamma-ray, X-ray, ultraviolet and optical wavebands simultaneously.

Swift will use three onboard telescopes that can quickly identify and monitor the wavelengths of gamma-ray bursts, which are estimated to occur somewhere in space at least once a day.

The spacecraft can respond within about a minute or less after it detects a GRB. First, it rotates to the proper position so its onboard telescopes can view the burst. Then it monitors the afterglow, which can continue emitting X-rays, optical light and radio waves for periods lasting up to several weeks.

Swift also notifies several other companion telescopes worldwide that can react quickly to join the study.

Swift caps off a 30-year hunt to understand the nature of gamma-ray bursts, flashes of light that burn as brightly as a billion-billion suns, said Anne Kinney, director of NASA's Universe Division in Washington.

We expect to detect and analyze over 100 gamma-ray bursts a year, said Neil Gehrels, Swift's principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Md.

What scientists eventually will find from those detections and analyses remains speculative. The link between some GRBs and black hole formation seems solid, but the bursts also could be caused by two neutron stars merging or even a pair of black holes orbiting each other. Hence, one of Swift's missions is to determine whether GRBs produce different energy levels.

Some bursts likely originate from the farthest reaches, and hence earliest epoch, of the universe, said John Nousek, Swift's mission director and a professor of astronomy and astrophysics at Penn State University. Swift's Mission Operations Center is located at PSU campus in University Park, Pa.

They act like beacons shining through everything along their paths, including the gas between and within galaxies along the line of sight, Nousek said.

Another of Swift's primary missions will be to watch for GRBs that might originate within the Milky Way galaxy. On that question, the interest might be more than purely scientific.

Astronomers suspect that a powerful burst occurred here just a few thousand years ago, from W49B, a supernova remnant only 35,000 light-years away. At one time, W49B was a supermassive star that blew itself up, then collapsed into a black hole. The question is whether it, too, created a burst in the process.

The nearest known gamma-ray burst to Earth is several million light years away -- most are billions of light years distant - so the detection of the remnant of one in our own galaxy would be a major breakthrough, said William Reach of the California Institute of Technology.

W49B is barrel-shaped and ringed by bright, hoop-like structures that can be seen in the infrared range of light. It also exhibits intense X-ray emissions produced by concentrations of iron and nickel ions along the axis of the barrel.

This makes it a prime candidate for being the remnant of a gamma-ray burst, said Jonathan Keohane of NASA's Jet Propulsion Laboratory in Pasadena, Calif.

At this distance, the structure is a comfortable curiosity. That would not be the case if Earth's solar system was located, say, within a few hundred light-years of W49B. Then, the X-ray jets would blind observers on Earth and orbiting spacecraft alike with radiation equivalent to 10 quadrillion suns.

Which raises the question: What if a burst did happen that close to Earth?

History provides one clue. A paper presented earlier this year by Adrian Melott of the University of Kansas Department of Physics and Astronomy, suggests a mass extinction that occurred during the late Ordovician period, about 440 million years ago, could have been caused by a GRB.

Due to expected severe depletion of the ozone layer, intense solar ultraviolet radiation would result from a nearby GRB, Melott wrote. Some of the patterns of extinction and survivorship at this time may be attributable to elevated levels of UV radiation reaching the Earth.

In addition, a GRB could trigger the global cooling which occurs at the end of the Ordovician period that follows an interval of relatively warm climate. Intense rapid cooling and glaciation at that time, previously identified as the probable cause of this mass extinction, may have resulted from a GRB.

A discussion of such effects is hardly academic, because there is at least one nearby star that might be big enough to collapse into a black hole someday.

Betelgeuse, located about 400 light-years away and occupying the constellation Orion's right shoulder - and easily visible in the sky in the fall and winter in the northern hemisphere -- is a red giant more than 600 times wider than the sun. If the two switched places, Betelgeuse's surface would swallow up Earth and the inner planets and reach almost to Mars.

Though a relatively young star, Betelgeuse also is aging very rapidly. The sun has an estimated remaining life expectancy of 4 billion or more years, but Betelgeuse may not make it through the next 5 million.

As red giants do, it is consuming its nuclear fuel so fast it will not be able to resist the pull of gravity much longer. When that happens, Earth-based observers will know, because Betelgeuse will destroy itself in a supernova explosion, which will be visible here even in daylight.

The question is whether Betelgeuse has enough mass to collapse into a black hole and cause a gamma-ray burst.

It is an important distinction. Debris - in the form of gas and particles - from the supernova could cause problems on Earth, but not for hundreds or thousands of years after the light from the explosion arrived. Humanity would have some time to prepare.

In the case of a GRB, however, the radiation would arrive at the same time as the light. Unless deep space outposts of the time gave some warning, the event could come as a rude awakening.

A case of severe disruption in the stellar neighborhood.

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NASA Launches Swift, To Track Gamma Rays
Washington (AFP) Nov 20, 2004
NASA launched Saturday its Swift satellite, which will track huge explosions of gamma rays, the US space agency said. The Delta rocket launcher lifted of from Cape Canaveral at 12:16 pm, according to NASA, which televised the launch live.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Computers take over

It may sound a lot like the plot of “The Terminator,” but computer technology is advancing daily and some believe that self-aware machines could become self-replicating and take over. After all, there are few areas of life where computers don’t intrude — they run banks, hospitals, stock markets and airports. Previously, computers were only as good as the humans using them, but artificial intelligence has the potential to create independently acting machines capable of outsmarting or destroying their creators.

Renowned scientist Stephen Hawking thinks computers could be a threat and argues that humans should be genetically engineered in order to compete with the phenomenal growth of artificial intelligence. In a recent interview he even said, “The danger is real that they could develop intelligence and take over the world.” The idea of a computer takeover may sound absurd, but you never know, we could be in the Matrix right now.

Answers and Replies

Ordinary thunderclouds are known to emit gamma rays, particle beams and hurl anti-matter, so these things obviously aren't too terrible. How can there be any harm in gamma rays from farther away?

Respectfully submitted,
Location: Seattle, WA

Gamma Radiation affects more than just the ozone layer. Given a large enough burst of Gamma rays there would be extensive injuries over the exposed hemisphere of the Earth. Marine life would be affected near the surface nearly as much as those on land, with the protection increasing the further down you go underwater.

In light of the recent CERN CLOUD results, and the probable importance of gamma rays on cloud formation, has anyone thought about the possible climatic effects of gamma ray bursts from a nearby super nova? (I was thinking mainly of Betelgeuse at 640 ly, which could go off any moment in the next million years.)

I note that super nova remnant" [Broken] has been discovered at 650-700 ly, the explosion of which should have been visible on Earth roughly 1250 AD. (Unreported in Europe and China, but it was in the southern sky, constellation Vela.)

And I'll also note that the first signs of the" [Broken] also occurred roughly 1250 AD, but that's probably just a coincidence.

The gamma rays (synchrotron or brehmsstrahlung?) developed above thunderstorms are already part of the influence of weather. They've always been there, but only recently were they discovered.

The antimatter particles mentioned are positrons, and for gammas to produce positron-electron pairs, they must have a minimum energy of

1.022 MeV. So what is the accelerating potential or process?

What is the anistropy of the gammas from thunderstorms?

In considering the effect of GRBs, one should consider the likely energy spectrum (low MeV vs 10-100 MeV range) and intensity, photon density or flux.

The gamma rays (synchrotron or brehmsstrahlung?) developed above thunderstorms are already part of the influence of weather. They've always been there, but only recently were they discovered.

The antimatter particles mentioned are positrons, and for gammas to produce positron-electron pairs, they must have a minimum energy of

1.022 MeV. So what is the accelerating potential or process?

I've been wondering about this myself, since the answers could resolve a number of questions in my mind.
This article explains how charge separation can be created, structured, propagated and maintained in ice. This may be an important factor in explaining how some clouds can gather the energy necessary to generate the electron showers required to cause gamma rays and antimatter formation. The investigators find that at low temperatures water ice will preferentially form a crystalline structure that maintains the alignment of the water molecule dipole, thereby preserving charge separation. [Broken]
This paper delves into how charge separation and "long-range" alignment of molecular dipoles is achieved at room temperature with the simplest of inputs - water, sunlight and an hydrophilic surface. Liquid crystal in a gel-like form is involved. Pollock, one of the authors, suggests this process may be fundamental to nucleation and formation of clouds in the first place.

In thunderclouds it is thought that charges in the supercooled water are separated with positive at the top and negative at the bottom. If a column within the cloud on the order of a mile or two were structured in such a way that the molecules were more or less uniformly aligned, I can imagine the potential for a very powerful discharge. Here is where my science comes to a stop. It would be fun to hear what answers there are to be found!