The History Channel: The Universe (started tonight)

[rrw4rusty]

Hi,

 

Anyone see this??? We had company and I only caught glimpses... they showed a spiral of gas from some binary system where one star was a super giant due to go nova soon (soon being relative). They talked about GRB (Gamma Ray Bursts) that might take place when it went super nova and said the stars axis was pointing at us and showed how the GRB might hit Earth.

 

Did anyone see this... know what star they were talking about... know how far away?

 

Yeah... well, in any event (pun intended)... just how big of a diameter would this GRB beam have? They show a beam a little less then the diameter of the Earth hitting Earth. I can't believe that a beam that size would smack Terra from that distance! Aren't we a moving target (you know, like orbiting around the sun is nothing else). I kind of think that the diameter of the GRB beam is 'much' larger by the time it gets to Sol and that it'd probably hits most of our solar system. That little animation of a beam hitting Earth had to be for 5th graders, yes?

 

Wish I'd see more of the show.

 

Anyone know how gamma rays kill? Anyone know if anything can shield one from these things? Maybe tin foil on the head? Seriously, just curious.

 

Rusty

[Arch2008]

Hi Rusty. You can watch whole episodes of "The Universe" again here:

 

http://www.history.com/content/universe/the-universe-video

 

I saw this episode too. I don't recall the designation given to the stars, but they were several thousand light years away. IIRC, most GRBs happen outside the Milky Way, so one in the MW would be of concern. When a huge star collapses into a black hole, creating a GRB, something like the mass of the Sun is converted into energy in one second. I suppose that the beam starts out with a diameter less than that of its star (the Sun's diameter is more than a million kilometers) and then would become more and more diffuse as it propogated toward the Earth. Such a beam would strike at the speed of light with no warning. The beam would be so energetic that the ozone would be depleted, causing mass extinctions as the surface of the Earth would no longer be shielded from the harmful radiation of our own Sun for many years thereafter. Exactly how GRBs form and work has only been discovered in the last twenty years or so, and is a topic of on-going research. The Earth may have already had an encounter with a GRB at what is known as the PreCambrian Extinction event. Just as we are searching for asteroids that are Near Earth Objects and might some day pose a threat, so some scientists are looking at nearby stars for possible GRB threats. The star in the broadcast might be a candidate at some point over the next million years.

[Airbrush]

That was a fascinating new episode of "The Universe". That is my favorite program. The giant binary is estimated at 8,000 light years away. I would also suppose the GRB beam, when the star goes supernova, would diffuse somewhat over such a great distance, but the experts think that the effects of that GRB would be very bad for Earth. It could be an ELE (extinction level event). The other estimate I heard was GRB may hit Earth about once every Billion years. We see them in other galaxies every day! The threat of NEOs is greater, but the threats of global warming and nuclear weapons detonation are much greater yet.

 

About the mechanics of a GRB, did they say something about the jets are powered by matter-antimatter annihilation? How is antimatter created during a supernova?

 

There is discussion about this on the History Channel discussion board, though the quality of discussion is not as good as here.

 

http://boards.history.com/forum.jspa?forumID=800000060&start=0

Edited August 19, 2009 by Airbrush

[Arch2008]

In James Kaler's book, "Extreme Stars", he addresses what he labels Hypergiant stars. The core of a hypergiant is so compact that in addition to normal fusion, particle pairs are also created in abundance. At some critical point, particle-antiparticle pairs are annihilating at such a rate that the resulting gamma rays superheat the star’s core and it erupts (something called pair instability).

[Airbrush]

Interesting stuff Arch. Does it also require rapid rotation of the death star and extreme magnetic fields to create antimatter?

[Arch2008]

IIRC, he just mentioned pressure from the sheer mass of the hypergiant crushing the core to the point that particle-antiparticle pairs were created along with the action of fusion. Of course, the spin and magnetic field of the star are always present, so their effect should be as well. I'll check his book again tonight.

[Airbrush]

My guess is that the only reaction known that can produce that much energy is matter-antimatter annihilation. Does that also account for the energy release of a supernova or hypernova? Maybe the long GRBs, that are thought to be collapsing giant stars, must be rapidly rotating in order for a GRB jet to form. Otherwise the beam cannot break through the surrounding gas and dust?

[insane_alien]

fusion reactions can produce that much energy. there's no need to bring large quantities of antimatter out of nowhere to explain it.

[rrw4rusty]

The immense energy of GRBs was explained in a previous History Universe series something like this:

 

When the black hole is formed not all of the matter is captured by it and this matter squirts outward as pure energy but over a very brief period and at very high energy levels.

 

The example of hitting an orange with a sledge hammer (or Gallagher's watermelon trick) was used to show how this 'squirt' occurs.

 

I don't recall antimatter being mentioned but I could be wrong. If this were to happen you'd want to be in a deep cave or on the other side of the Earth however, eventually the side effects would catch up with you.

 

It'd be a real bad day.

 

Rusty

[Arch2008]

Here's a link to a site James Kaler has:

http://www.astro.illinois.edu/~jkaler/glpa/update08.html

 

"At the top are the GRBs, which are (we think) caused by high mass hypernovae, which, because of their increasingly fast rotation as they collapse, produce focused bi-polar bursts of gamma rays. These in turn light up their surroundings in visual "afterglows." That from GRB 089319B hit an all time record of visual magnitude 5.4 even though 7.5 billion light years away! All things being equal (which of course they are not), the absolute magnitude must have been around -35. Don't get too close. Eta Carinae may blast out an energetic GRB. The rotation axis, however, happily points elsewhere."