Source

Bit of a worry and yet somehow very cool. And kind of amazing that we just happen to be right in the firing range, as it were.

Not to worry too much, Ins0mniac...

Estimating the exact directionality of a Gamma Ray burst from this system would be a wee difficult. But the odds of a precise alignment that would just so happen to hit our tiny littler planet, some 8000 ly distant are pretty darn slim...

Kind of interesting. Perhaps, gamma ray bursts may not be a danger to Earth, the Milky Way, or other life habitats in similar galaxies, since these supernova related events may be unlikely to occur where life would develop. Planets need metals to form (everything besides H and He), and low-metal galaxies would probably have fewer rocky planets and their moons.


MEASURED METALLICITIES AT THE SITES OF NEARBY BROAD-LINED TYPE IC SUPERNOVAE AND IMPLICATIONS FOR THE SN-GRB CONNECTION

"We compared the properties of our host sample with the properties of five nearby SN-GRB hosts, for which we derived chemical abundances using the same three metallicity diagnostics as for SN without observed GRBs. Broad-lined SN Ic without GRBs tend to consistently inhabit more metal-rich environments, and their host galaxies, for the same luminosity range (−17 < MB (host galaxy luminosity) < −21 mag), are systematically more metal-rich than corresponding GRB host galaxies. The trend is independent of the choice of diagnostic and cannot be due to selection effects as we include six SN found in a similar non-targeted manner as GRB-SN.

Article



Protecting Life in the Milky Way: Metals Keep the GRBs Away

Studies of GRB hosts at z ~ 1 reveal that they are underluminous compared to the general population of star-forming galaxies (e.g., Le Floc'h et al. 2003; Fruchter et al. 2006), suggesting that GRBs occur preferentially at low metallicities. In our analysis we study the five low redshift (z </= 0.25) GRBs, a complete sample of "local" bursts identified so far. In all cases these GRBs were followed by well-documented supernovae. This sample now includes GRB060218, whose host is fainter than the Small Magellanic Cloud (Modjaz et al. 2006). There are several reasons why this sample is worth a separate study. Good abundance information exists for the hosts of all five events, and it can be compared directly and using the same techniques to the sample of local star-forming galaxies from the Sloan Digital Sky Survey (SDSS) spanning approximately the same redshift range.

The highest redshift in the sample, z = 0.25, corresponds to look back time of ~ 2/3 of the age of the Earth, about the time when life on Earth could be affected by GRB radiation. At these small distances we might also see other impacts of GRBs, such as production of cosmic rays and shell remnants. With five well-studied events at hand, for the first time there are enough data in this interesting redshift range to make a direct and statistically significant empirical study. This investigation complements the high-z studies and it directly addresses the properties of nearby GRBs and their hosts, in case they are different.

The main result of our analysis is to show that the oxygen abundances of the five hosts, which range from ~ 0.1 to ~ 0.5 of the Solar value, are much lower than would be expected if local GRBs traced local star formation independently of metallicity. We conclude that GRBs are restricted to metal-poor stellar populations, in agreement with recent theoretical models of their progenitors (e.g., Yon & Langer 2005; Woosley & Heger 2006), and that the Milky Way and other large spirals have been too metal-rich to host GRBs for the last several billion years (see also Langer & Norman 2006). We discuss several implications of this result. We also find that the gamma ray isotropic energy release, Eiso, for these five GRBs declines with increasing oxygen abundance of the host galaxy, and suggest that the oxygen abundance threshold for a "cosmological" GRB (visible at high redshifts) may be as low as 0.15 of the Solar value.

Article



Nature 398, 487-489 (8 April 1999) | doi:10.1038/19033; Received 21 October 1998; Accepted 1 February 1999

A Dusty Pinwheel Nebula Around the Massive Star WR104 Wolf-Rayet

(WR) stars are luminous, massive blue stars thought to be the immediate precursors to some supernovae. The existence of dust shells around such stars has been enigmatic since their discovery about 30 years ago, as the intense ultraviolet radiation from the star should be inimical to dust survival. Although dust creation models, including those involving interacting stellar winds, have been put forward to explain these dust shells, the high-resolution observations needed to distinguish between the models have hitherto been lacking.

Here we present images of the dust outflow around WR104, obtained using a technique that allows us to resolve detail on scales of about 40 AU at the distance of the star. Our images (taken at two epochs) show that the dust forms a spatially confined stream that follows precisely a linear (or archimedian) spiral trajectory with a rotation period of 220 +/- 30 days, viewed at an angle of 20 5° from the pole. These results prove that, in this case, a binary companion is responsible for the creation of the circumstellar dust. Moreover, the spiral plume makes WR104 the prototype of a new class of circumstellar nebulae, which are unique to systems with interacting winds.

Article

Hubble Space Telescope

In 1998, a team of astronomers detected gamma-ray burst "as bright as the rest of the universe", releasing a hundred times more energy than previously theorized. (looking down the barrel effect?)

The team measured the distance to a faint galaxy from which the burst, designated GRB 971214, originated. It is about 12 billion light-years from Earth. The astronomers used a suite of satellites and ground-based telescopes to follow the burst. This Hubble image of the GRB 971214 field was taken about four months after the burst, well after the afterglow had faded away. The extremely faint and distant object marked with an arrow is the host galaxy of the gamma-ray burst.

Gamma Ray Burst 971214 - W. M. Keck Observatory

"Most of the theoretical models proposed to explain these bursts cannot explain this much energy," said Kulkarni. "However, there are recent models, involving rotating black holes, which can work."

Beside, we couldn't really *do* anything about it anyway. Better to worry about that which has a higher probability of happening, and that we can possibily do something about.

I agree with MID and Lilly, the chances of the Earth being hit must be astronomically slim, and even if we were sure the Earth was going to be struck, what could you do about it?...

As always, Lil, the impeccability of your logic brings the whole thing into clear focus!

I see. So I don't have to be kept awake at night in a cold sweat after all. heheh.

Nope...no need to be an insomiac, Ins0mniac!

Something told me not to post. I will heed my better impulse, next time.

Real Death Star Could Strike Earth Charles Q. Choi
Special to SPACE.com
SPACE.com
2 hours, 47 minutes ago



A beautiful pinwheel in space might one day blast Earth with death rays, scientists now report.

Unlike the moon-sized Death Star from Star Wars, which has to get close to a planet to blast it, this blazing spiral has the potential to burn worlds from thousands of light-years away.


"I used to appreciate this spiral just for its beautiful form, but now I can't help a twinge of feeling that it is uncannily like looking down a rifle barrel," said researcher Peter Tuthill, an astronomer at the University of Sydney.


The fiery pinwheel in space in question has at its heart a pair of hot, luminous stars locked in orbit with each other. As they circle one another, plumes of streaming gas driven from the surfaces of the stars collide in the intervening space, eventually becoming entangled and twisted into a whirling spiral by the orbits of the stars.


Short fuse


The pinwheel, named WR 104, was discovered eight years ago in the constellation Sagittarius. It rotates in a circle "every eight months, keeping precise time like a jewel in a cosmic clock," Tuthill said.


Both the massive stars in WR 104 will one day explode as supernovae. However, one of the pair is a highly unstable star known as a Wolf-Rayet, the last known stable phase in the life of these massive stars right before a supernova.


"Wolf-Rayet stars are regarded by astronomers as ticking bombs," Tuthill explained. The 'fuse' for this star "is now very short — to an astronomer — and it may explode any time within the next few hundred thousand years."


When the Wolf-Rayet goes supernova, "it could emit an intense beam of gamma rays coming our way," Tuthill said. "If such a 'gamma ray burst' happens, we really do not want Earth to be in the way."


Since the initial blast would travel at the speed of light, there would be no warning of its arrival.


Firing line


Gamma ray bursts are the most powerful explosions known in the universe. They can loose as much energy as our sun during its entire 10 billion year lifetime in anywhere from milliseconds to a minute or more.


The spooky thing about this pinwheel is that it appears to be a nearly perfect spiral to us, according to new images taken with the Keck Telescope in Hawaii. "It could only appear like that if we are looking nearly exactly down on the axis of the binary system," Tuthill said.


The findings are detailed in the March 1 issue of Astrophysical Journal.


Unfortunately for us, gamma ray bursts seem to be shot right along the axis of systems. In essence, if this pinwheel ever releases a gamma ray burst, our planet might be in the firing line.


"This is the first object that we know of that might release a gamma ray burst at us," said astrophysicist Adrian Melott at the University of Kansas in Lawrence, who did not participate in this study. "And it's close enough to do some damage."


This pinwheel is about 8,000 light years away, roughly a quarter of the way to the center of the Milky Way Galaxy. While this might seem far, "earlier research has suggested that a gamma ray burst — if we are unfortunate enough to be caught in the beam — could be harmful to life on Earth out to these distances," Tuthill said.


What might happen

Although the pinwheel can't blast Earth apart like the Death Star from Star Wars — at least not from 8,000 light years away — it could still cause mass extinction or possibly even threaten life as we know it on our planet.

Gamma rays would not penetrate Earth's atmosphere well to burn the ground, but they would chemically damage the stratosphere. Melott estimates that if WR 104 were to hit us with a burst 10 seconds or so long, its gamma rays could deplete about 25 percent of the world's ozone layer, which protects us from damaging ultraviolet rays. In comparison, the recent human-caused thinning of the ozone layer, creating "holes" over the polar regions, have only been depletions of about 3 to 4 percent, he explained.

"So that would be very bad," Melott told SPACE.com. "You'd see extinctions. You might see food chain collapses in the oceans, might see agricultural crises with starvation."

Gamma ray bursts would also trigger smog formation that could blot out sunlight and rain down acid. However, at 8,000 light-years away, "there's probably not a large enough effect there for much of a darkening effect," Melott estimated. "It'd probably cut off 1 or 2 percent of total sunlight. It might cool the climate somewhat, but it wouldn't be a catastrophic ice age kind of thing."

Cosmic ray danger

One unknown about gamma ray bursts is how many particles they spew as cosmic rays.

"Normally the gamma ray bursts we see are so far away that magnetic fields out in the universe deflect any cosmic rays we might observe from them, but if a gamma ray burst was pretty close, any high-energy particles would blast right through the galaxy's magnetic field and hit us," Melott said. "Their energies would be so high, they would arrive at almost the same time as the light burst."

"The side of the Earth facing the gamma ray burst would experience something like getting irradiated by a not-too-distant nuclear explosion, and organisms on that side might see radiation sickness. And the cosmic rays would make the atmospheric effects of a gamma ray burst worse," Melott added. "But we just don't know how many cosmic rays gamma ray bursts emit, so that's a danger that's not really understood."

It remains uncertain just how wide the beams of energy that gamma ray bursts release are. However, any cone of devastation from the pinwheel would likely be several hundred square light-years wide by the time it reached Earth, Melott estimated. Tuthill told SPACE.com "it would be pretty much impossible to for anyone to get far enough to be out of the beam in a spaceship if it really is coming our way."

Don't worry

Still, Tuthill noted this pinwheel might not be the death of us.

"There are still plenty of uncertainties — the beam could pass harmlessly to the side if we are not exactly on the axis, and nobody is even sure if stars like WR 104 are capable of producing a fully-fledged gamma-ray burst in the first place," he explained.

Future research should focus on whether WR 104 really is pointed at Earth and on better understanding how supernovae produce gamma ray bursts.

Melott and others have speculated that gamma ray bursts might have caused mass extinctions on Earth. But when it comes to whether this pinwheel might pose a danger to us, "I would worry a lot more about global warming," Melott said.

Top 10 Ways to Destroy Earth
Despite Rumors, Black Hole Factory Will Not Destroy Earth
The Strangest Things in Space
Original Story: Real Death Star Could Strike Earth
Visit SPACE.com and explore our huge collection of Space Pictures, Space Videos, Space Image of the Day, Hot Topics, Top 10s, Multimedia, Trivia, Voting and Amazing Images. Follow the latest developments in the search for life in our universe in our SETI: Search for Life section. Join the community, sign up for our free daily email newsletter, listen to our Podcasts, check out our RSS feeds and other Reader Favorites today!