Gamma is typically produced by nuclear decay and is often where "missing mass" goes via the E = mC^2 so they are not an electron phenomena but a nuclear phenomena.
While some gamma rays come from nuclear decay, that is far from the entire story. Most of the gamma rays we observe from space originate in particle interactions, mostly proton on proton collisions. As two protons interact, a whole slew of different particles are produced, but mainly pions. The neutral pion decays into two gammas.
On the other hand, in many astrophysical sources, blazars for example, gamma rays are produced through inverse Compton-scatterings.
One way to avoid having charges produce photons is to have your particle partly consist of the EM field. For example, although the experiment has never been done, I think (if you are a particle theorist feel free to correct me!) you could annihilate two Z bosons to give two photons because the Z consists partly of an EM field.
I am curious as how you would make that Feynman diagram. Myself, I cannot make it work.
That statement is not what most astrophysicists would say. The Galactic center contains so many "normal" astrophysical sources that it is more likely to to detect dark matter in the halo or in dwarf galaxies.
To be that hot, that it only shines in gamma, what could it be made of?
Obviously it is some form of degenrate matter, but can a quark-star get that hot?
Does this level of heat, require a size so small that a quark-star is not suffiecient?
Just wondering, does anyone have a calc as to how hot something realatively-big like
a nuetron star should be vs. how hot something much smaller like a quark-star should
be? Can we measure the size of the beam source by some means?
Why do you assume that the gamma-ray radiation is thermal, which it in fact is not.
But I still don't see how neutral matter can produce radiation? Thermal radiation occurs because of electrons jumping between energy levels
Thermal radiation is solely due to the fact that the object has a temperature. Planck's law describes the spectrum of the radiation emitted by a black body.
but in an all neutron soup, there's no jumping (none that I can imagine). Moreover, how can neutron matter produce a magnetic field (I'm probably just missing some known mechanism)?
Indeed. See below.
I can see that charged matter interacting with the magnetic field produces radiation (just like the northern/southern lights) but my question is where does that field come from? Is there perhaps a neutron --> proton + electron --> neutron reactions that occur on a regular basis with radiation being a byproduct?
Yes. As you found out yourself, a neutron star is not perfect. There is always a small percentage of protons and electrons, mostly in the surface crust. As the neutron star is rapidly spinning, this creates a strong magnetic field.
What? That's ridiculous logic. I've used the dock on OS X (a little bit, anyway) and it's wonderful, except that you can't tell if something is running or not.
And here I thought the little shiny "blob" under the icon indicated a running app in MacOS X.
Yes you are correct that you have to have access to a car, but that's not really what you wrote in your first post "The former requires having a car". I know plenty of people who cannot afford a car, still they have a drivers license. Most of them got it using their parents' or a friend's car.
Not that I am saying that a homeless person is likely to have a drivers license.
4) Driver's License or SSN - The former requires having a car, while the latter, again is given without any cost whatsoever. Just walk into the office and ask for one.
Really? You have to own a car to get a driver's license? This must be a new law.
Impressive indeed! This also reminds me when I took a Pascal class in high school. We didn't do as much programming as fooling around since our teacher was a total geek too. A friend of mine was paying around with a floppy disk and all of a sudden DOS would report it as several GB. Of course, all data stored on it was corrupted.
1. Brown dwarves, planetoids, flotsam and jetsam of the cosmos, known as MaCHOs (Massive Compact Halo Objects).
Far too few such objects are observed to make it a plausible explanation. Also, it is not a plausible explanation for the mass distribution seen in clusters of galaxies where the mass distribution DOES NOT match the galaxy distribution.
2. Particles that do NOT interact through Strong Force (proton bonding with help from neutrons), Weak Force (decay of electron orbits) or Electromagnetism.
Just to correct you, the strong interaction couples to color charges of quarks and gluons. Atomic nuclei are held together due to residuals of of the strong interaction.
The weak interaction is not about decaying electron orbits. Neutron beta decay is a weak interaction.
Re:The LHC should be destroyed
on
LHC Success!
·
· Score: 1
It's pretty obvious you have absolutely no idea what you're talking about
In the first place, our current understanding is that black holes DO dissipate, through Hawking Radiation.
That's only a theoretical prediction. It has never ever been proved experimentally.
When interstellar dust hits the atmosphere,the resulting energy discharge can form tiny black holes, and fairly often.
Talking about being misinformed. Interstellar dust is FAR from energetic enough. Not even VHE or UHE cosmic rays produce black holes. There's no experimental evidence what so ever for your claim.
Sorry to say this, but it seems you need to revisit some basic physics.
Not only is the poster wrong about how the silicon microstrip tracker works, he is also wrong about how the total energy of the incident gamma ray is determined. The energy is measured by the calorimeter and that has nothing to do with Planck's law.
I used to do work study for some of the folks working with the GLAST project at Iowa State University their website is here and has some more information about Gamma Ray Astrophysics.
Why not link to the official Fermi (GLAST) websites directly www-glast.stanford.edu and http://glast.gsfc.nasa.gov/, instead of linking to an institution who has not contributed significantly to GLAST?
Well, python+numpy in a single cpu environment can be very fast, depending on what you want to calculate. But you completely miss the point; for really computing intensive work you have to go parallel, and I have yet to see anything in Java that works efficiently in a parallel environment.
You are absolutely right that python+numpy code can be a whole lot faster than c++ code and also easier to write. I have used python+numarray (the numpy predecessor) for a while and it is amazing what you can do. But there are limitations to this too. For example; what do you do when you want to work on that 10000x10000x10000 grid in a simulation. Answer: you look to parallel computing, which is not a strength of python+numpy.
Have you the slightest clue about how computing intensive cosmology simulations are? Even on our 96 node cluster, a single simple run takes on the order of several days to finish. I have yet to see any Java/C#/Python code that can compete.
I have been involved in developing code for simulating cosmic-ray acceleration in expanding supernova remnants, this in Python. It is incredibly slow and we can only compute on small grid sizes.
Granted, on your little home desktop or even workstation, your managed code will do just fine. But that is on a completely different level. It is like comparing oranges and coconuts.
Have you ever tried writing a large-scale simulation code, for say dark matter/cosmology or cosmic-ray propagation in Java or C#? Please let me know when your code has finished executing.
neutron stars emit radio waves at regular intervals.
No, that's a pulsar, a subclass of neutron stars which are highly magnetized and rotating. Most of the neutron stars we know of are pulsars but there are also radio-quite neutron stars out there.
First of, its not only X-rays. AGNs are observed in all wavebands, from radio to TeV gamma rays.
Secondy, as so many have already pointed out, BHs are predicted to radiate "Hawking radiation" but such radiation has never been observed.
Z**2 is only 5% better than tungsten but it's denser. That or iridium.
They're more expensive than tungsten, but for a space instrument the cost of materials is nothing compared to the cost of launch. That is incorrect. Yes, the launch is expensive, but the instrument is not cheap either. Its a very complex detector and the components are not inexpensive. I do not have any exact figures, but we are talking a multi-million dollar detector here.
---
Btw, I should add that I used to be a member of the GLAST collaboration.
Some relevant documents:
http://heseweb.nrl.navy.mil/glast/CALPDR/PDR_Summary_Report_16July.pdfhttp://www-glast.slac.stanford.edu/software/AnaGroup/Atwood-GLASTEnergy-9dec02.ppt
According to the preliminary design report, the calorimeter is 8.5 radiation lengths deep, with 1.5 in the tracker. I forget my shower mechanics but 10 rad lengths seems like enough. The design goal is 20% accuracy for a high-energy range, and 10% and 6% at progressively lower energies.
This stuff makes me feel lucky that I work with lots of lead glass and PMTs. What is enough in terms of shower containment depend on what you want to do. To detect GeV photons, 10 radiation lengths is plenty enough. For a 100 GeV photon, there will be shower leakage, especially if the photon has a large incident angle. As one can expect, the LAT was optimized to allow detection up to a few hundred GeV.
My guess is that the secondaries in turn generate photons. Incoming gamma yields neutrons and ions (for example), ions and neutrons make more lower energy gammas, etc etc. As gamma rays at these energies are not too common, it is possible that the detector even can resolve individual "showers" of secondaries.
Correct me if I'm wrong, but this is my intuition. You are almost right. The dominant interaction in the high-energy regime is pair-production (as long as there is some material to interact with). When the gamma ray hits one of the interaction layers in the GLAST tracker, it produces an electron-positron pair. These secondaries will also interact (bremsstrahlung) and produce more secondary gammas and e-p pairs. This is a well known concept called electromagnetic showering in particle physics. By studying the shower one can determine incoming direction etc. However, energy measurement is better done with a calorimeter. Almost all high-energy particle experiment use calorimeters to measure particle energies. Someone else already described this in a post. The GLAST LAT has both a silicon microstrip tracker and a CsI calorimeter.
Slashdot Mirror
Gamma is typically produced by nuclear decay and is often where "missing mass" goes via the E = mC^2 so they are not an electron phenomena but a nuclear phenomena.
While some gamma rays come from nuclear decay, that is far from the entire story. Most of the gamma rays we observe from space originate in particle interactions, mostly proton on proton collisions. As two protons interact, a whole slew of different particles are produced, but mainly pions. The neutral pion decays into two gammas.
On the other hand, in many astrophysical sources, blazars for example, gamma rays are produced through inverse Compton-scatterings.
One way to avoid having charges produce photons is to have your particle partly consist of the EM field. For example, although the experiment has never been done, I think (if you are a particle theorist feel free to correct me!) you could annihilate two Z bosons to give two photons because the Z consists partly of an EM field.
I am curious as how you would make that Feynman diagram. Myself, I cannot make it work.
That statement is not what most astrophysicists would say. The Galactic center contains so many "normal" astrophysical sources that it is more likely to to detect dark matter in the halo or in dwarf galaxies.
You need to brush up on your basic particle physics. The standard model does not agree with what you state above.
To be that hot, that it only shines in gamma, what could it be made of? Obviously it is some form of degenrate matter, but can a quark-star get that hot? Does this level of heat, require a size so small that a quark-star is not suffiecient?
Just wondering, does anyone have a calc as to how hot something realatively-big like a nuetron star should be vs. how hot something much smaller like a quark-star should be? Can we measure the size of the beam source by some means?
Why do you assume that the gamma-ray radiation is thermal, which it in fact is not.
But I still don't see how neutral matter can produce radiation? Thermal radiation occurs because of electrons jumping between energy levels
Thermal radiation is solely due to the fact that the object has a temperature. Planck's law describes the spectrum of the radiation emitted by a black body.
but in an all neutron soup, there's no jumping (none that I can imagine). Moreover, how can neutron matter produce a magnetic field (I'm probably just missing some known mechanism)?
Indeed. See below.
I can see that charged matter interacting with the magnetic field produces radiation (just like the northern/southern lights) but my question is where does that field come from? Is there perhaps a neutron --> proton + electron --> neutron reactions that occur on a regular basis with radiation being a byproduct?
Yes. As you found out yourself, a neutron star is not perfect. There is always a small percentage of protons and electrons, mostly in the surface crust. As the neutron star is rapidly spinning, this creates a strong magnetic field.
What? That's ridiculous logic. I've used the dock on OS X (a little bit, anyway) and it's wonderful, except that you can't tell if something is running or not.
And here I thought the little shiny "blob" under the icon indicated a running app in MacOS X.
Yes you are correct that you have to have access to a car, but that's not really what you wrote in your first post "The former requires having a car". I know plenty of people who cannot afford a car, still they have a drivers license. Most of them got it using their parents' or a friend's car.
Not that I am saying that a homeless person is likely to have a drivers license.
4) Driver's License or SSN - The former requires having a car, while the latter, again is given without any cost whatsoever. Just walk into the office and ask for one.
Really? You have to own a car to get a driver's license? This must be a new law.
Most of the other guys spent most of the time playing Doom or Rise of the Triad. At least I and a few others played around coding.
Impressive indeed! This also reminds me when I took a Pascal class in high school. We didn't do as much programming as fooling around since our teacher was a total geek too. A friend of mine was paying around with a floppy disk and all of a sudden DOS would report it as several GB. Of course, all data stored on it was corrupted.
1. Brown dwarves, planetoids, flotsam and jetsam of the cosmos, known as MaCHOs (Massive Compact Halo Objects).
Far too few such objects are observed to make it a plausible explanation. Also, it is not a plausible explanation for the mass distribution seen in clusters of galaxies where the mass distribution DOES NOT match the galaxy distribution.
2. Particles that do NOT interact through Strong Force (proton bonding with help from neutrons), Weak Force (decay of electron orbits) or Electromagnetism.
Just to correct you, the strong interaction couples to color charges of quarks and gluons. Atomic nuclei are held together due to residuals of of the strong interaction.
The weak interaction is not about decaying electron orbits. Neutron beta decay is a weak interaction.
It's pretty obvious you have absolutely no idea what you're talking about
In the first place, our current understanding is that black holes DO dissipate, through Hawking Radiation.
That's only a theoretical prediction. It has never ever been proved experimentally.
When interstellar dust hits the atmosphere,the resulting energy discharge can form tiny black holes, and fairly often.
Talking about being misinformed. Interstellar dust is FAR from energetic enough. Not even VHE or UHE cosmic rays produce black holes. There's no experimental evidence what so ever for your claim.
Sorry to say this, but it seems you need to revisit some basic physics.
Not only is the poster wrong about how the silicon microstrip tracker works, he is also wrong about how the total energy of the incident gamma ray is determined. The energy is measured by the calorimeter and that has nothing to do with Planck's law.
I used to do work study for some of the folks working with the GLAST project at Iowa State University their website is here and has some more information about Gamma Ray Astrophysics.
Why not link to the official Fermi (GLAST) websites directly www-glast.stanford.edu and http://glast.gsfc.nasa.gov/, instead of linking to an institution who has not contributed significantly to GLAST?
Btw, I used to work with GLAST.
Well, python+numpy in a single cpu environment can be very fast, depending on what you want to calculate. But you completely miss the point; for really computing intensive work you have to go parallel, and I have yet to see anything in Java that works efficiently in a parallel environment.
You are absolutely right that python+numpy code can be a whole lot faster than c++ code and also easier to write. I have used python+numarray (the numpy predecessor) for a while and it is amazing what you can do. But there are limitations to this too. For example; what do you do when you want to work on that 10000x10000x10000 grid in a simulation. Answer: you look to parallel computing, which is not a strength of python+numpy.
Have you the slightest clue about how computing intensive cosmology simulations are? Even on our 96 node cluster, a single simple run takes on the order of several days to finish. I have yet to see any Java/C#/Python code that can compete. I have been involved in developing code for simulating cosmic-ray acceleration in expanding supernova remnants, this in Python. It is incredibly slow and we can only compute on small grid sizes. Granted, on your little home desktop or even workstation, your managed code will do just fine. But that is on a completely different level. It is like comparing oranges and coconuts.
Have you ever tried writing a large-scale simulation code, for say dark matter/cosmology or cosmic-ray propagation in Java or C#? Please let me know when your code has finished executing.
neutron stars emit radio waves at regular intervals.
No, that's a pulsar, a subclass of neutron stars which are highly magnetized and rotating. Most of the neutron stars we know of are pulsars but there are also radio-quite neutron stars out there.black holes emit nothing.
Everybody else has already shot this one down.First of, its not only X-rays. AGNs are observed in all wavebands, from radio to TeV gamma rays. Secondy, as so many have already pointed out, BHs are predicted to radiate "Hawking radiation" but such radiation has never been observed.
Finally someone who knows what he is talking about.