21–30 of 37 posts
Earlier quoted context omitted.
Maybe they mean it was the first time for that particular galaxy?
First time for any galaxy, that we know of.
We are talking here of the first time a short burst of only a few minutes was detected from a source not previously known.
Distant galaxies with super massive black holes in their center are a well known source of this kind of gamma radiation. Known as active galactic nuclei and especially blazars
Earlier quoted context omitted.
Are people on Earth safe from GRBs?
Depends on the GRB. A supernova 50 light years away is supposed to eliminate all large animal life (including us). Fortunately any stars capable of it are more than 100 Ly away, where they would only eliminate, e.g., civilization. A magnetar quake 500 light years away would sterilize the planet (but not harm the magnetar at all). Fortunately, the nearest magnetar we know about is 9000 light years away, so its blast w…
“ Gamma rays are the highest-energy form of radiation, with wavelengths that can be smaller than the nucleus of an atom. (Radio waves, for comparison, have wavelengths ranging between about a millimeter to hundreds of kilometers.)” This is so insane to me. I knew the wavelengths were small but not this small. Nature is so cool!
The energies we detect go into the hundreds of TeVs and charged cosmic rays have been detected to much, much higher energies.
Earlier quoted context omitted.
Its not really wrong. The atmosphere absorbed most of it but some made it through because there was so much of it. The atmosphere happens to absorb most of the high energy wavelengths involved, it also absorbs many low energy wavelengths. There are 'windows' of wavelengths which get to pass through to different degrees. The details are intricately grasped by quantum electrodynamics, but don't really lend themselves t…
I think it does actually. A gamma ray is just light, we would expect the signal to get attenuated early on in the atmosphere. This particular one had enough oomph to punch down to ground level instruments and actually generate a response. Either it lucked out statistically and had a momentary straight shot to the ground (I mean, it could happen), or the thing had so much energy it ploughed straight through anything t…
We are talking about single particles of light having energies between ~ 50 GeV and up to 10 TeV (for this GRB, other sources go even higher).
At these energies, the atmosphere is completely opaque and the gamma rays are absorbed at around 20 km height.
However, the process kicks of a cascade of particles, the gamma ray is absorbed by creating an electron-positron pair, each with half the energy. These particles then create new gamma rays via bremsstrahlung and those gamma rays again are absorbed via pair production creating a cascade of high energy particles.
The charged part of this cascade (electrons and positrons) are moving faster than the speed of light in air and are thus producing Cherenkov radiation, which is in the UV to the visible range.
It is this light our telescopes detect and from this light we reconstruct the original properties of the first gamma ray that entered the atmosphere.
Earlier quoted context omitted.
Depends on the GRB. A supernova 50 light years away is supposed to eliminate all large animal life (including us). Fortunately any stars capable of it are more than 100 Ly away, where they would only eliminate, e.g., civilization. A magnetar quake 500 light years away would sterilize the planet (but not harm the magnetar at all). Fortunately, the nearest magnetar we know about is 9000 light years away, so its blast w…
What about Eta Carinae?
Astrophysicist here, I'm currently finishing my PhD, mainly focused on data analysis for the kind of telescopes that measured this GRB, while my main focus is on a smaller prototype telescope (FACT), I also work for the one that detected this GRB (MAGIC). AMA ;)
Earlier quoted context omitted.
Are people on Earth safe from GRBs?
Depends on the GRB. A supernova 50 light years away is supposed to eliminate all large animal life (including us). Fortunately any stars capable of it are more than 100 Ly away, where they would only eliminate, e.g., civilization. A magnetar quake 500 light years away would sterilize the planet (but not harm the magnetar at all). Fortunately, the nearest magnetar we know about is 9000 light years away, so its blast w…
Is it unlikely that we are far enough to be mostly safe from these threats?
Or maybe it's one filter for Fermi paradox (on a planet that isn't far from these kinds of threats life wouldn't survive long enough to develop civilization).
“ Gamma rays are the highest-energy form of radiation, with wavelengths that can be smaller than the nucleus of an atom. (Radio waves, for comparison, have wavelengths ranging between about a millimeter to hundreds of kilometers.)” This is so insane to me. I knew the wavelengths were small but not this small. Nature is so cool!
Doesn't really make sense to speak of wavelengths at these energies any more. For all intents and purposes, these are particles. The energies we detect go into the hundreds of TeVs and charged cosmic rays have been detected to much, much higher energies.
Astrophysicist here, I'm currently finishing my PhD, mainly focused on data analysis for the kind of telescopes that measured this GRB, while my main focus is on a smaller prototype telescope (FACT), I also work for the one that detected this GRB (MAGIC). AMA ;)
Is there an archive with all the data ever received, or is the "uninteresting" data dropped after some time?
Unfortunately all ground based telescopes until now keep their data private but nothing is thrown away ;) We have several Million air showers recorded.
This is going to change with the next gen observatory, which will operate as an open observatory.
Earlier quoted context omitted.
I think it does actually. A gamma ray is just light, we would expect the signal to get attenuated early on in the atmosphere. This particular one had enough oomph to punch down to ground level instruments and actually generate a response. Either it lucked out statistically and had a momentary straight shot to the ground (I mean, it could happen), or the thing had so much energy it ploughed straight through anything t…
This is not really how things work. We are talking about single particles of light having energies between ~ 50 GeV and up to 10 TeV (for this GRB, other sources go even higher). At these energies, the atmosphere is completely opaque and the gamma rays are absorbed at around 20 km height. However, the process kicks of a cascade of particles, the gamma ray is absorbed by creating an electron-positron pair, each with h…
Thank you for that. I figured there were processes in there I wasn't aware of,and that fits with my mental model a lot better than something I kicked out while falling asleep.