Friday, June 16, 2023

4055 - GAMMA RAY BURSTS - what is the largest?

 

-    4055  -  GAMMA  RAY  BURSTS  -  what is the largest?     What was the brightest cosmic explosion of all time?  A jet of particles pierces a star as it collapses into a black hole during a typical gamma-ray burst.   This jet was created by gamma-ray burst 221009A.




------------------   4055   -   GAMMA  RAY  BURSTS  -  what is the largest

-    Few cosmic explosions have attracted as much attention from space scientists as the one recorded on October 22, 2022, and named the Brightest of All Time (BOAT). The event, produced by the collapse of a highly massive star and the subsequent birth of a black hole, was witnessed as an immensely bright flash of gamma rays followed by a slow-fading afterglow of light across frequencies.

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-   Since picking up the BOAT signal simultaneously on their giant telescopes, astrophysicists the world over have been scrambling to account for the brightness of the gamma-ray burst (GRB) and the curiously slow fade of its afterglow.

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-   The initial burst was angled directly at Earth and it also dragged along an unusually large amount of stellar material in its wake.  But what remained a puzzle was that the edges of the jet could not be seen at all.

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-    The slow fade of the afterglow is not characteristic of a narrow jet of gas, and knowing this made astronomers suspect there was an additional reason for the intensity of the explosion, and their mathematical models have borne this out.

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-    The GRB had a unique structure, with observations gradually revealing a narrow jet embedded within a wider gas outflow where an isolated jet would normally be expected."

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-    So what made this GRB wider than normal? The researchers have a theory.   GRB jets need to go through the collapsing star in which they are formed, and what we think made the difference in this case was the amount of mixing that happened between the stellar material and the jet, such that shock-heated gas kept appearing in our line of sight all the way up to the point that any characteristic jet signature would have been lost in the overall emission from the afterglow.

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-    These GRBs must be directed straight towards us when they happen, as it would be unphysical for that much energy to be expelled in all directions at once.

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-     The exceptionally long GRB 221009A is the brightest GRB ever recorded and its afterglow is smashing all records at all wavelengths. Because this burst is so bright and also nearby ( it occurred at the minor distance of 2.4 billion light years from Earth), we think this is a once-in-a-thousand-year opportunity to address some of the most fundamental questions regarding these explosions, from the formation of black holes to tests of dark matter models.

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June 12,  2023       GAMMA  RAY  BURSTS  -  what is the largest?       4055

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