Mar 03 2008
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WR 104: A nearby gamma-ray burst?
I spend a lot of time in my upcoming book Death from the Skies! making the case that for the most part, astronomical dangers to life on Earth — especially from explosions called gamma-ray bursts — are incredibly rare, and not worth fretting over too much.
I may — may — have to change my mind.
Note: Let me be clear up front, since folks tend to worry about these things: I’m going to talk about some frightening things in this post, but my personal opinion as someone who has actually studied this stuff is that we are in no real danger. The object I’ll be describing is pretty interesting, but there are way too many uncertainties about it to cause any panic for now. So remain calm, keep your arms and legs inside the blog entry at all times, and enjoy. If you want more reassurance, just skip to my conclusion below.
Up until now, I hadn’t heard of WR 104.
This is a binary star located 8000 light years away, more or less
toward the center of our galaxy. The two stars are both whoppers; one
is a massive O star, which will someday detonate in a tremendous
supernova. However, at that great distance, it won’t do anything more
than be a bright light in the sky.
The other star in the system is a bit of a worry, though. It’s what’s called a Wolf Rayet star, a massive, luminous star that is on the brink of exploding as well. In general, these also blow up as supernovae and, from 8000 light years away (80 quadrillion kilometers) it wouldn’t pose much of a threat.
But what if it explodes as a gamma-ray burst?
GRBs are a special type of supernova. When a very massive star explodes, the inner core collapses, forming a black hole, while the outer layers explode outwards. Due to a complex and fierce collusion of forces in the core, two beams of raw fury can erupt out of the star, mind-numbing in their power. Composed mostly of high-energy gamma rays, they can carry more energy in them than the Sun will put out in its entire lifetime. They are so energetic we can see them clear across the Universe, and having one too close would be bad.
Enter WR 104. The brighter of the two stars might, just maybe kinda possibly, be ready to go GRB on us. It’s not at all clear if it can, and there is reason to believe it can’t (young stars like this one tend to have characteristics that make it very hard for them to form an actual GRB). Also, even if it does blow up that way, the beams are a double-edged sword; yes, they pack an unbelievable punch, but they’re narrow. A GRB would have to be aimed precisely at us to damage us, and the odds of that are pretty low.
Except that for WR 104, it’s possible the star does have us in its sights.
The only way to know which direction a potential GRB’s beams will blast out is to look for some signs in the system of symmetry; a disk of gas, for example, would orbit the star’s equator, so the poles of that disk would be the direction the beams would follow. WR 104 does have a feature that allows us to determine its orientation — a vast spiral of material being ejected from the system.
The picture above was taken using the Keck infrared telescope in Hawaii. It shows the material being ejected. Both stars have strong winds of material they blow, like super-solar winds. These winds collide, and flow outward from the binary. The streaming gas forms a spiral pattern in the same way a rotating lawn sprinkler shoots out water. The gas doesn’t actually move along the spiral arms; that’s a bit of an illusion caused by the rotation of the system (comets sometimes show this same pattern).
University of Sydney astronomer Peter Tuthill, who has been studying WR 104 since it was discovered in 2000, has also created a dramatic movie showing the spiral pattern generated as the two stars orbit each other. The animation shown here is an older one — a newer one that is much cooler is available, but at 400kb I’ll simply link to it — but it gives you an idea of what’s going on.
The thing to note is that we really are looking at this spiral almost face-on, more-or-less down the pole of the system (it appears to be tilted by about 12 degrees from face-on, but it’s difficult to measure, and could be tilted by anything from 0 - 16 degrees — Tuthill’s technical paper has details). It’s hard to say exactly, but it’s close enough to make me wonder.
What would happen if WR 104 were to go all GRB on us?
One thing is that it would be incredibly bright. How bright is actually hard to say; GRBs are notoriously variable in brightness, and there may be quite a bit of dust between us and the system that would absorb a lot of the visible light. The major concerns from a GRB at this distance are two-fold: the impact of the high energy radiation, and the impact of subatomic particles called cosmic rays.
Models of a GRB exploding at roughly the same distance indicate that the immediate impacts are damage to the ozone layer, and the creation of nitrogen dioxide, which is basically smog. Gamma rays emitted by the burst would hit ozone molecules and shatter them, and models indicate that a GRB at this distance could deplete the ozone layer by 30% globally, with local pockets depleted by 50%. It would take years for the ozone to recover from that. Note that the ozone holes we have been dealing with the past few years are actually depletions of less than 5%. Obviously, this is a big deal.
Also, the gamma rays would break apart molecules of nitrogen in our air, which would reform as nitrogen dioxide, a reddish-brown gas that is essentially smog. This could potentially block sunlight, cooling the Earth. That may sound nice, given the reality of global warming, but in fact we’d rather not have something like this happen when we don’t understand all the implications. Plus, nitrogen dioxide is water soluble, and would precipitate down as acid rain.
So all that would be bad.
Worse, the flood of subatomic particles from such a GRB may in fact
be more dangerous. These cosmic rays hit the air and create fast
particles called muons, which would rain down over the Earth. How bad
is that? Actually, it’s pretty uncertain; the number of variables
involved is large, and the modeling of this is notoriously difficult.
It’s not even clear that the cosmic rays from a GRB at this distance
would even reach us, and if they did, what exactly would happen. The
worst-case scenario is pretty bad — large scale mass extinctions — but
I am not sure anyone really believes those models. The best case
scenario is that they never reach us at all, so the range is a bit
wide. 
There’s just too much we don’t know.
Another issue is that the distance to WR 104 is uncertain. It may be 8000 light years, but other astronomers think it may be as close as 5000 light years. That does make a difference, since the damage it can inflict is sensitive to distance. Farther away is better! Tuthill’s team thinks 8000 light years is a better estimate, so that’s good.
Finally, we don’t know when such a star will explode. It could be tonight, or it may be thousands of years from now. So it’s not worth losing sleep over this!
To wrap up: WR 104 is an interesting system. Both stars are guaranteed to explode one day. If they are just regular old supernovae, then we are in no danger at all, because they are way way too far away to hurt us (a regular supernova has to be about 25 light years or closer to hurt us, and WR 104 is 300 times farther away than that). It is possible that one of the stars may explode as a GRB, and it’s possible it’s aimed at us, but we don’t know. And we don’t know exactly what effects it would have on us. So if it’s less than 10,000 years from exploding and if it blows up as a GRB and if it’s aimed at us and if there isn’t much junk between us and it, then yeah, we may have a problem. But that’s an awful lot of ifs.
Given all these uncertainties, and having researched the dangers of GRBs extensively for my book, I won’t be losing any sleep over WR 104. For now, this is just an extraordinarily cool object, and it’s worth keeping an eye on — certainly for its astronomical interest alone! But as for it being a Death Star, I think it’s way way too early to tell.
Tip o’ the lead-lined beanie to The Daily Telegraph.
AAAGGGHHHHH!!! We’re all gonna die! We’re all…
Uh… wait a minute…
We *are* all gonna die.
[Mal Reynolds look]
Huh.
[/Mal Reynolds look]
And of course the thing that will keep me up at night is that it’s possible that it _already has_ exploded, and we just won’t notice until just before the GRB gets here.
Interesting. Although, the odds of getting the Earth affected are really low. Is there any estimated percentage?
Um, at the risk of outing myself as an idiot, how could it be that astronomers don’t know how far away WR 104 is?
Aren’t supernovae supposed to be associated with all kinds of weird asymmetric “kicks” anyway, so there’s no guarantee the GRB jet will be aligned with the present rotation axis?
Quick! Make a YouTube video before someone else does!
WR104.org anyone?
“Um, at the risk of outing myself as an idiot, how could it be that astronomers don’t know how far away WR 104 is?”
Past a few lights years its much more difficult to measure the distance of stars because parallax can’t be used. Light intensity is used instead and is harder to draw out an estimate.
stopgap is more or less correct. In this case, the brightness of the stars won’t help much, because the intrinsic brightness of stars in this stage is difficult to pin down.
The astronomers tried to use the measured speed of the winds from the stars compared to the actual expansion of the spiral arm. If it moves x arcsecdons per year, and you know the wind is moving at 1000 km/sec, then you can get a distance. The problem is the wind speed is very difficult to measure from the spectra. That’s why there’s some uncertainty.
@stopgap,
Wow, that’s really interesting. I remember seeing Phil comment once that we aren’t really sure how far away the Andromeda galaxy is and since then, I’d been meaning to ask how that could be. A three thousand light year margin of error in a 3-8K LY distance estimate seems like an alarmingly high lack of certainty about our universe.
It’s funny how as a layman, I am usually so blissfully certain that the scientist types pretty much have everything figured out at this point about everything that I’m surprised when it turns out there’s a lot left to know…
Peter - distances to objects are probably the single hardest thing to measure in astronomy (well, that and anything that depends directly on knowing the distance… for example, while it’s easy to measure how bright an object appears from the earth, you need to know its distance precisely to figure out its intrinsic luminosity - and in fact, because brightness falls off as distance squared, uncertainties in distance propogate into uncertainties about twice as large in luminosity!).
In the solar system, we can use radar ranging to get direct distances. For nearby stars, we can use parallax (shifting of nearby objects compared to background objects as we move around the sun), but it becomes more or less useless past 100pc. Aside from a few other funky geometrical methods (the moving cluster method is a nice one - if a cluster of stars are all moving in the same direction, they appear as if they’re all converging to a point in the sky whose position depends on how far away they are. There’s also a few edge-on maser disks in nearby galaxies that you can use to get geometric distances), most of the time you have to make assumptions about how intrinsically luminous an object is and then see how much dimmer it appears from earth.
In this case, the distance is actually geometric, so it doesn’t require that many assumptions, but as Phil says, the true wind velocity isn’t known very well.
[TMB]
Someone’s going to say it sooner or later…
It’s already blown, it’s on the way, and it’ll be here on…
wait for it…
December 21, 2012!!!!!
(snork)
So, let me get this straight.
What you’re actually saying is that we’re all in incredible danger and we better plan now? (by adopting the new religion/not washing the car/hiding/gathering in public areas/writing out congressman/blaming foreigners/what’d I leave out?).
@Christopher
“December 21, 2012″
I was thinking the same thing. I think I’m going to write a book about how great the Mayan were at astronomy, far more advanced then historians give them credit (and sighting several examples from other “new age” writers). Then I’ll explain how they discovered gamma ray burst hundreds of years ago and that their observations showed that this doom was impending. They predicted the date, and now the BA has given the final evidence to show that this is possible, and therefore, my conclusion must be true. I’ll make a fortune, enough to be able to either disappear when Dec 22, 2012 roles around, or at least enough to hired someone to weasel me out of the jam.
Or maybe I’ll just go home and watch some more Doctor Who…
Aren’t feeding black holes usually generate focused X rays out of the poles instead of gamma rays ?
Anyway lets hope we will not win this lottery!
I assume that using a big mirror shield will be enough to deflect the GRB, right?
Right?
TMB–didn’t Hipparcos direclty measure distances out to ~1k parsecs? Or am I being naive in thinking that measured distance ~ 1/angular resolution?
Anyhow, it looks like the planned Gaia mission (http://www.rssd.esa.int/index.php?project=GAIA&page=index) aims to measure a billion stars with 10’s of micro-arc-sec accuracy, which should at least tell us where WR 104 is. Damm, but we build cool spacecraft these days!
Does anyone have a reference to those studies about the effects on the ozone layer? I think the lifetime of stratospheric ozone is pretty short, so the system should return to equilibrium quickly after a shock…and besides, wouldn’t a gamma ray turn an ozone molecule into 3 O’s? Those should find O2’s to recombine with in seconds.
(And no, that’s not a denial that CFCs were a problem…CFC’s hang out in the stratosphere long enough to shift the equilbrium)
As the Earth’s magnetic field weakens on its way to reversing, ordinary cosmic rays may become more and more of a hazard here on Earth, right? Imagine if WR104 happened to go GRB on us at the same time as our magnetic field was down!
Any idea what the duration of a GRB would be? If it happened to hit us, how long would we be bombarded with cosmic rays & gamma radiation? Seconds, days, decades?
So apart from building a Dyson Sphere with a really thick shell, what are potential protections from GRBs?
Incredibly nifty stuff.
Thanks for the explanation, Phil. And yeah, the idea that maybe it did
go kaboom already and the stuff is on its way here is a bit unsettling,
but what exactly can we do about it? It really is pretty nifty how
things that far away could affect life clinging to a dinky little rock
all the way over here.
Questions:
1. Is there a spacetime “horizon” similar to the line of sight limited by the horizon at sea?
2. If it takes light a year to travel 1 lightyear (=9.463×10^17 meters), at 1 lightyear/year, how does the light ever reach us?
And meant to add: I’m sure your new book mentions what, exactly, we could do about GRBs, and what it would take to do it and how effective it would be and how likely we would be to do such a thing. But if the burst was on the way and was scheduled to arrive next week… well, oh well.
How long would the gamma ray stream last? I know typically, they can last anywhere from a few seconds to minutes, but what are the expectations here? Is this another major variable we have little understanding of? Also, what about the stream of cosmic rays, how long will those bombard us? Since they’re a product of the gamma rays generated, then would they last as long as the gamma rays? Furthermore, couldn’t we launch a flat piece of lead of some diameter at a heading towards the star spewing the rays? At least we could try to mitigate the problem by reducing the amount of exposure on earth. Solutions anyone?
@Sean: Pretty much nothing. If we get to be SO DAMN UNLUCKY that we get with by a GRB, we’re pretty much hosed.
@ drew terry
1. no space time horizon AFAIK not in the observable universe.
2. guess what, it reaches us by traveling the distance! ( surprise! )
Speed of Light is approx. 3×10^5 km/sec (300,000)
we see the objects as they were, when the light left the objects towards our way. By looking in the sky you see backwards in time (8000 years for those stars)
Tuthill - the originator of this story - is just down the corridor from me.
Since gamma rays travel at the speed of light, the main problem to any possible contingency/defence is that we wouldn’t know it was coming until the exact moment it hits us.
If we knew enough about stellar evolution to be able to precisely predict when the star would go supernova based on what we observe now, we could in theory know whether or not it has already blown if we knew the exact distance. Say it was 8000 light years away and we were able to determine from the light we observe that it was 5000y from blowing, then we’d know that it actually blew 3000y ago.
If we could figure the exact time the GRB would hit us it might be conceivably possible to put up some kind of shield in orbit and time it so that it would eclipse the GRB at exactly the right moment and block the beam from hitting the earth.
Not knowing the exact time, our only hope would be to erect some kind of orbital shield and keep it up indefinately (or at least for the several thousands to hundreds of thousands of years that we think it will take for the star to blow). I have no idea how much that would cost and it would also block out the sun, so it would do more harm than good.
Here we are talking about a star in our galaxy, the assumed distance of which varies by more than 60%. Now consider that it gets much more difficult to measure the distance to objects the farther away they are and the distance just from our galaxy to the next is unfathomable (for me anyways).
My point? When you read articles about the data collected from observing gravitational lensing and even just far far away objects (outside our galaxy) how can scientist be so assertive about their interpretation of the data? I constantly read articles about how some team of astronomers discovered all this information about some early early galaxy. I’m assuming understanding the distance to the gravitational lense and to the subject behind it would be key to understanding what is being viewed via the gravitational lense.
Can anybody explain to me how they can be so sure, or if (I hope this is not the case) they are making more assumptions than they are letting on in the majority of their reports?
The hobbits were right, we should live in holes in the ground.
Really, really deep holes.
“Imagine if WR104 happened to go GRB on us at the same time as our magnetic field was down!”
Since gamma rays aren’t effected by magnetic fields, there would be no change.
Even a cosmic ray/muon event would be unlikely to effect the atmosphere as much as nuclear testing did on the 50’s.
And since the centre of the galaxy is in the Southern hemisphere, the northern hemisphere breadbaskets would largely be unaffected.
You’d give penguins sunburn. And maybe koalas. But the ozone layer down here is gone already.
So the biggest disruption would probably be the grounding of commercial airliners whenever Sagittarius is above the horizon. Think of the Woo that would generate.
With regards to manyguns:
I may be in error on this, but I think that distance measures for distant galaxies can be more certain than those of stars in our own galaxy because we actually have more reliable methods of measuring distances for them. For example, we can use Type Ia supernova in those galaxies as standard candles with known luminosity so we can calculate the distance pretty precisely, or doppler shift in their spectra.
I am assuming, since you didn’t mention it that the pair are not lined up with the orbit plane of the solar system. If it were/is would that give us a little better probabilty (however small) of protection by being behind the sun or one of the other (unlucky) planets?
Apparently something like this has already happened. In the Ward/Brownlee book “Rare Earth” they mention SGR 1900+14 which went off on August 27, 1998. SGR as in Soft Gamma Repeater. Apparently this event was significant enough to lower the altitude of the earth’s night-time ionosphere from 90 km to 60 km and screw up satellite communications for all satellites on that side of the planet. The Ulysses spacecraft recorded a surge in gamma rays from the normal background of 200 counts per half-second to more than 100,000 counts per half-second. We think that SGR 1900+14 is located about 20,000 light-years away. Ward and Brownlee speculate about what would have happened if it was located 200 light-years away. The pulse would have been 10,000 times as strong (one billion counts per half-second) and possibly could have reached to the surface of the earth.
Now I must admit that this kind of stuff scares the crap out me. There is absolutely no warning at all and when the pulse arrives it reaches its maximum within a few seconds. Perhaps for a really close SGR all higher forms of life on the earth facing the source would receive a lethal dose of radiation. Humans, dogs, and cats would all be gone with only the cockroaches surviving. So roughly half the population would be wiped out within a few minutes. Not sure if the physics behind SGR’s is similar to GRB’s.
Anyway, here is a web site talking about SGR 1900+14:
http://solomon.as.utexas.edu/~duncan/magnetar.html#August_27
“On August 27, 1998 a giant flare from SGR 1900+14 set new records for the most intense flux of gamma-rays ever detected from a source outside our solar system. It blitzed gamma-ray and X-ray detectors on seven different spacecraft at locations throughout the solar system. Especially useful data were recorded by three experiments: the Russian Konus detector on the geo-space science Wind space probe which was orbiting near the Sun-Earth equilibrium point (”L1″), upstream of the Earth in the solar wind; the Italian-Dutch Beppo-SAX gamma-ray/X-ray observatory, in low Earth orbit; and a gamma-ray detector aboard the Ulysses spacecraft, a joint effort of the European Space Agency and NASA that was orbiting the Sun in a polar orbit at roughly the distance of Jupiter.
NASA’s Rossi X-ray Timing Explorer (RXTE), another Earth-orbiting X-ray observatory, was pointed away from SGR 1900+14 when the burst occured, but it nevertheless recorded a strong signal. High-energy photons were diffusing through the metal shields surrounding its X-ray detectors. However, one proven workhorse for SGR studies, the Burst and Transient Source Experiment (BATSE) aboard NASA’s orbiting Compton Gamma-ray Observatory, detected nothing. The BATSE team, led by mild-mannered Charles Meegan (who is BATSE-MAN) ran out of luck that day: the Compton Observatory was on the far side of the Earth at the time of the flare.
The flare hit the Earth on it’s night side, in the zenith over the western Pacific Ocean, at 1:22 A.M. Hawaii time. It was intense enough to strongly ionize the Earth’s outer atmosphere, affecting radio communications.”
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I just learned about the wr104 in a newspaper. And i have some questions
1. how big are the chances that this will happen in our lifetime? any percent estimates?
2. With the technology we have today, is it not possible to know if it hits us before it actually hits?
question number 1 is the most important.
@LabLamming:
I know the magnetic field doesn’t do squat against gamma rays (photons have no charge), but it does plenty to divert charged cosmic rays.
Question about parallax:
Would putting the parallax-measuring satellite around Jupiter instead of Earth give a 5-fold improvement in resolution? ’cause, you know, the bigger orbit.
B.A. wrote:
[quote]GRBs are a special type of supernova.[/quote]
Waaaaaaait a minute … I thought that if it produced a Gamma-Ray Burst (as a result of its core collapsing into a black hole), we called it a [b]hyper[/b]nova.
Jackie:
1) Dunno. Pretty tiny I would think.
2) Gamma rays travel at the speed of light. Information cannot travel faster than the speed of light. So the earliest we could know about it is when it is here.