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Gamma Ray Burst Heterogeneity
[[Mod. note -- I apologise for the delay in this posting's appearance.
Richard S. Sternberg E-mailed it to me on 18.Sept.2007, but I was travelling and had with limited internet access at the time. -- jt]] I've watched YA (yet another) History Channel popularizer program, and the scientists here know that always brings me back to an exploration of the hypothesis I've asked about before. I have YA technical question to ask the group. The television program explains that studies from the Dutch gamma ray satellite led to confirming observations of long GRB afterglow in the visible light band. Measurement of the redshift in those afterglows led to confirmation that long GRBs are uniformly distant from us, fairly uniformly around .8 redshift, or thousands of light years away, about half-way across the observable universe. As such, the consensus of scientists conclude, the energy released is so unimaginably great that it would be around the energy level of converting the entire universe into gamma rays. Further observations suggest that the best hypothesis for factoring down the energy level is a collimated beacon from a collapsar. But, my question steps back a bit to the first step of these observations. Isn't the consistency of the long distance to long GRBs a clear violation of the principle of homogeneity? Is there some explanation in the Big Bang Theory why the super neutron stars that are theorized to become collapsars are all so far away? Alternatively, if GRBs (or, at least, some GRBs) are the result of boundary collisions as the Big Bang overtook matter-energy in a larger external Universe, wouldn't the energy from collisions at or near the time of the BB be significantly time-stretched, such that they would appear to be further away than they were? Isn't this difference testable? If the GRBs are all from the edge of the observable universe, couldn't we use the data from redshifts in surrounding afterglow to map the phenomenon? If the result is homogenous, wouldn't that be the null hypothesis (for me) and tend to prove that it's just a kind of star going nova? If the result is a multi-dimensional shape, what can that shape be other than the shape of the boundary of the Big Bang or a projection from it? As a second question, does anyone here know whether the findings from the Swift satellite, monitored by Penn State, have yet provided enough data on short GRBs to determine a curve of distances based on redshifts in the afterglows? Do we know the range of distances and the normality and kurtosis of the curve of those distances? If we have the data, is it homogenous? Does anyone know to whom I might write or call to pursue this line of thought? TIA! -- Richard S. Sternberg, Esq. |
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Gamma Ray Burst Heterogeneity
Richard S Sternberg wrote:
The television program explains that studies from the Dutch gamma ray satellite led to confirming observations of long GRB afterglow in the visible light band. Measurement of the redshift in those afterglows led to confirmation that long GRBs are uniformly distant from us, fairly uniformly around .8 redshift, or thousands of light years away, about half-way across the observable universe. Probably then you meant "billions of light years away", not "thousands". Further observations suggest that the best hypothesis for factoring down the energy level is a collimated beacon from a collapsar. But, my question steps back a bit to the first step of these observations. Isn't the consistency of the long distance to long GRBs a clear violation of the principle of homogeneity? Is there some explanation in the Big Bang Theory why the super neutron stars that are theorized to become collapsars are all so far away? If you model the situation in your mind, maybe, just maybe, the "uniformity" of the distance isn't so strange. For sources much farther away, the received energy might be below the threshold of easy detection. For sources much closer, the combination of smaller numbers of them in a smaller volume, and the "collimated beam" not yet having spread enouugh to have a very large area to intersect our vicinity, might mean that in general they aren't going to hit our detectors very often. That would leave a shell of "most likely to be detected" sources, even IF homogeneity were still the real situation. Yes, I absolutely refuse to do the math to see if either of those intuitions makes numerical sense. xanthian. |
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Gamma Ray Burst Heterogeneity
In article , Richard S
Sternberg wrote: The television program explains... ... long GRBs are uniformly distant from us, fairly uniformly around .8 redshift, or thousands of light years away, about half-way across the observable universe. They are not all at the same redshift. Television lies. As a second question, does anyone here know whether the findings from the Swift satellite, monitored by Penn State, have yet provided enough data on short GRBs to determine a curve of distances based on redshifts in the afterglows? Do we know the range of distances and the normality and kurtosis of the curve of those distances? If we have the data, is it homogenous? The data is available at http://swift.gsfc.nasa.gov/docs/swif...ive/grb_table/ which lets you select the columns of the data table, including redshift. And yes, there is a large range in redshifts. There are a lot of selection effects, so going from the distribution of redshifts to the history of GRB production rates is a big job, fraught with uncertainty. -- David M. Palmer (formerly @clark.net, @ematic.com) |
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Gamma Ray Burst Heterogeneity
The television program explains that studies from the Dutch gamma ray
satellite led to confirming observations of long GRB afterglow in the To set the record properly straight: BeppoSAX was an Italian-Dutch mission, not Dutch only (but the Dutch did discover the first GRB afterglow). But, my question steps back a bit to the first step of these observations. Isn't the consistency of the long distance to long GRBs a clear violation of the principle of homogeneity? Is there some explanation in the Big Bang Theory why the super neutron stars that are theorized to become collapsars are all so far away? Nothing about the Big Bang theory, but it appears that the progenitors of long-GRBs (collapsars indeed: massive stars), prefer a low- metallicity environment: the further back in time you go, the lower the amount of metals wil be, so GRBs will tend to be found at higher redshift. It even looks like (but that's yet not really statistically confirmed) long GRBs follow a different formation curve than the general star-formation curve, peaking at larger redshift. Other than that, there are also observational biases, which may lead to a somewhat underestimate of GRBs at certain redshift (although that's accountable), and the Universe is of course simply larger at redshift 1 than at current. As a second question, does anyone here know whether the findings from the Swift satellite, monitored by Penn State, have yet provided enough data on short GRBs to determine a curve of distances based on redshifts in the afterglows? Do we know the range of distances and the normality and kurtosis of the curve of those distances? If we have the data, is it homogenous? There are about a dozen redshifts for short bursts, not enough for all the details. There are indeed closer-by (suiting the picture of binary compact-object mergers, which need some time to merge), at redshifts in the range of 0.2 - 1 (although there are a few claims for z 1, but hard to secure). |
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Gamma Ray Burst Heterogeneity
For sources much closer, the combination of smaller
numbers of them in a smaller volume, and the "collimated beam" not yet having spread enouugh to have a very large area to intersect our vicinity, might mean that in general they aren't going to hit our detectors very often. That argument doesn't really work, because it assumes the beam ("jet") travels all the way from there to here, spreading al the time. The jet is, in fact, not even a light year long when first spotted, and certainly much smaller in diameter: it is the photons produced in the jet that we see, and these travel straight on towards Earth. The thing that matters here is the jet *pointing* in our direction, and whether the energy/outflow speed at the sides tapers off, meaning the jet edges would be harder to see. But whether that is true or not, the problem of the jet pointing in our direction is the same locally or at high redshift. |
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