Couple of questions about star nursery hypernovae

According to Professor Sir Martin Rees, the Astronomer Royal, these phenomena happen on what he calls “the other side of the universe” some 10 billion lightyears away (and therefore 10 billion years ago). They emit two incredibly energetic beams of gamma rays and are uniformly distributed across the entire sky.

Question 1: How is it that so many of these (in fact, all of them as far as I can tell) happen to have one beam aimed at earth such that they light up material between them and us? (Observing these lights is how they were redshifted.)

Question 2: Why do they appear as small circles of light in telescopes at all rather than lighting the entire sky, or at least much more of the sky, given that they have travelled practically the whole of spacetime?

They don’t all happen to be aimed at Earth. There’s many of them that we don’t see. We only see the ones where Earth happens to be in the path of one of the two beams.

We’re only going to see the light that comes directly from the hypernova to Earth. The light that misses Earth is just going to keep going until it hits something else.

But these are gamma rays. They are so powerful that were they to eminate from merely a few hundred million lightyears away, they might well destroy the earth. Their energy lights up matter in their path brighter than a million suns. It seems to me that the effect, unless the beam never widens, should be more like an aurora borealis than a small dot. And especially for those that do not directly aim at earth (I still find it odd that so many do), there should still be the lit up space dust, other stars, and planets.

What happens when a gamma ray hits a dust particle? Gamma rays have extremely high energy. Rather than just bouncing off a dust particle like visible light does, I suspect that the photon would either shoot right on past with only slight deflection or be absorbed by an atomic nucleus in the dust. I did a little poking around and couldn’t find any information about the gamma-ray scattering properties of interstellar dust, but x-ray scattering is observed for very small angles, creating only small haloes around x-ray sources such as Nova Cygni.

As for planets and stars, I’d think they would absorb gamma rays, not scatter them.

I appreciate your input, Pod, but it does fly in the face of what Rees said. These gamma ray emissions have so much energy that until a couple of years ago, scientists feared that they might invalidate e=mc[sup]2[/sup]. There are no lenses that focus gamma rays for observation, and so the scientists relied on observation of material that was illuminated into visible light by them. If you get a chance, watch his interview on the Science Channel’s “Death Star” program and let me know how I might have misinterpreted or misunderstood something. Thanks.

You’re not thinking about this clearly. The fact that the beam spreads out is immaterial to how you perceive it. The light from each and every star spreads out in every direction, yet we’re not seeing the image of the star covering the entire sky, are we? How large an object appears depends on two factors: it’s actual size, and the distance from you. This is easy to see if you get someone to point a flashlight at you from several hundred yards away. This is also a beam that spreads out, but from that distance you’ll see it as almost a pointlike object–just like the gamma ray emitters.

I’m afraid that I don’t get the Science Channel.

In gamma ray detectors, the materials that are used to create visible photons from gamma ray impacts aren’t just yer basic run-of-the-mill hunk of stuff. For example, the Compton Gamma Ray Observatory used large crystals of sodium dioxide. The Gamma Ray Large Area Telescope will use bars of CsI(Tl). I’m not sure what exact properties (other than high density) are required, but just piece of metal or rock won’t create the desired effect.

When the surface of the a planet (for example) is bathed in the light of a GRB, most of the gamma rays are simply absorbed, not reflected or scattered as visible light.

QED also has a good point about the flashlight.