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Origin of Cosmic Rays Revealed
neutron_p writes "An international team of astronomers has produced the first ever image of an astronomical object using high energy gamma rays, helping to solve a 100 year old mystery - an origin of cosmic rays. The astronomers studied the remnant of a supernova that exploded some 1,000 years ago, leaving behind an expanding shell of debris which, seen from the Earth, is twice the diameter of the Moon. Cosmic rays are extremely energetic particles that continually bombard the Earth, thousands of them passing through our bodies every day."
here.
Enjoy.
Welley Corporation - SLM Scammers
...of cosmic ray air-showers.
Thousands of cosmic rays do not pass through our bodies every day... They are stopped by the atmosphere. Cosmic rays are actually fairly dangerous radiation. During the Apollo missions, Astronauts would occasionally see flashes of light as cosmic rays hit their eyes... they also left 'streaks' in the porthole glass.
I think you are confusing them with neutrinos, but even then you are wrong... billions of those pass through us every second.
In a way, it makes sense that they'd be partly responsible for the blue in our atmosphere -- the rest comes from the Sun bombarding the layers of gases up there. Sometimes science is just a way of jerryrigging loose facts together to create a plausible test or explanation for strange phenonema.
Try not. Do or do not, there is no try.
-- Dr. Spock, stardate 2822-3.
They are called muons. There is a lot more than a thounsand per day! And they can do A LOT of damage. Oh, and muons are produced from cosmic ray interractions in the upper atmosphere.
an expanding shell of debris which, seen from the Earth, is twice the diameter of the Moon [unattributed quote from the original article]
So its diameter is a function of viewing position. Sounds like angular diameter. That's still huge, though not as huge as M31 in Andromeda.
Phooooey!
i ve/update.as p?id=15U3&style=update
e x.asp?issue=15
It chopped the end off my link.
I'll try again:
Here.
(The "Here" text above is DEFINATELY enclosed with correct HTML, and contains the full URL)
Hmmmmmmm, now thats interesting.
Slashcode is screwing the link up.
I will just paste it exact in plain text - it is balking on the "&style=update" parameter of the URL.
Here it is in plaintext:
http://www.pparc.ac.uk/frontiers/arch
and incase all that fails, this is a working link to the archived issue, the HESS link is on the left hand side:
http://www.pparc.ac.uk/frontiers/archive/issueInd
liqbase
...I have a web page describing how: here
-- SIGFPE
((1000 light-years)*(size of moon))/(moon orbital height)
across,
((9.5 × 10^18 meters) * (3,476,000m))/ (384,403,000 m)
That's about 86 light years in diameter. Its average velocity is left as an exercise to the homebound.
sigs, as if you care.
Make that 172 light years in diameter.
sigs, as if you care.
I was involved in a similar, but very much smaller scale, experiment for my MSc thesis (JANZOS), attempting to find detect gamma rays from the (then very recent) supernova 1987A in the Large Magellanic Cloud.
So supernovae were a prime suspect source back then.
We had three (not four) 2 metre (not 12 metre) telescopes with about 30 'pixels' each (compared to a few thousand for HESS.) (I actually worked on another part of the experiment, which used particle detectors to detect higher energy showers.)
A significant problem is to distinguish between showers created by gamma rays and ones created by charged particles (mostly protons.) The charged particle showers are 'uninteresting', because the direction they come from is uncorrelated to their source - they move on curved paths due to galactic magnetic fields. Unfortunately, they are about 99% of the cosmic rays. We were not able to distinguish, so we had a large 'signal to noise' problem.
There was a single telescope similar to these ones in the mid 80s (the Whipple Telescope, I think) which claimed to be able to distinguish by details of shower structure. (We didn't have the resolution, nor perhaps the light gathering power, to make use of this.) I presume HESS has built on this work.
Note that this result does not necessarily tell us about the very highest energy cosmic rays. There is a change in the slope of the spectrum at (from memory) about 10^15 electron volts, so it is likely that different processess are involved on either side of this boundary. I think there were also theoretical reasons to think that supernovae could not accelerate particles to such high energies.
As I recall, the models for acceleration generally required shock waves in a gas with magnetic fields. Particles could repeatedly bounce across the shock, getting accelerated each time. (Think of a ball bouncing between two walls that are moving towards each other.)
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
- Gamma rays are not cosmic rays
- Gamma rays do not cause Cherenchov radiation
Primary cosmics rays are subatomic particles with extremely high energy. The most energetic ones have an energy comparable to the energy of a tennis serve.Capacitance is a physical constant for a transistor. They do not change unless the physical characteristics of the transistor are changed.
Computers work based on changing voltages and currents, not changing capacitances. Its physically impossible to change capacitance without destroying the transistor.
Finally, cosmic rays are not "heavily charged extremely small particles". They do not have charge, and are not particles. Cosmic rays are high energy, short wavelength electromagnetic radiation- you can argue that cosmic ray photons are particles, but they are not conisdered particles in the normal sense of the word. And photons certainly do not have charge. When they strike a material, they can excite electrons, possibly even ionizing them, causing a change in charge stored in ram.
The group's publications page is here (click on observations section), but they don't seem to have a preprint of this paper. Nature will let you read the abstract of the paper for free.
The research seems to be just a more direct confirmation of something that was already thought to be understood, but had never really been verified.
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Missing mass:
The missing mass is not really missing anymore. We know how much of it there is, where it is, and what it is not (!), just not what it is. It comes in two forms: dark energy and dark matter. Dark matter is clumpy, non-baryonic, non-interacting (at least with normal matter, except via gravity) stuff. Without it, galaxies, galaxy clusters, and larger structures probably would not have formed. Dark energy is stranger stuff. It may or may not be related to the cosmological constant or to the vacuum energy. Dark energy is a pervasive, evenly distributed, massless, but anti-gravitating thing. (It's equation of state is near P = - pho: pressure equal to the negative of the density.) Our current understanding comes largly from the fabulous WMAP microwave anisotropy data.
EM radiation:
If there were *lots* more high energy EM radiation in our vacinity, we would have detected it, not directly, but through similar mechanisms to cosmic ray shower production in the atmosphere.
EM radiation does have energy and by Einstein has an effective mass. In the very early universe, there was enough radiation to contribute significantly to the mass budget of the universe, but today we estimate it to be roughly 1 part in 10000 of the total mass in the universe.
We can (relatively) easily measure gamma rays with a few MeV in energy. Once you get beyond a few MeV, single photons will interact with Cosmic Microwave Background photons and via pair production create pairs of particles like e+,e-. As energy goes up, these processes get really efficient so really high energy photons don't live very long (~10-100 kyr).
As the wavelength of a photon drops, its energy increases. Above a certain point (1.02 MeV), it becomes likely that the gamma ray will convert its energy into an electron-positron pair (with the excess energy as kinetic energy). The positron will most likely annihilate with a nearby electron and create two lower-energy gamma rays (0.51 MeV each). Today, pair production normally requires an interaction with a nucleus, but I think most high-energy photons in the universe formed elementary particles in the conditions following the big bang. (Someone correct me if I'm wrong...I'm not a physicist.) Anyway, such interactions would give us a way to detect and measure the amounts of super-high energy gamma in the universe.
Here is a summary of IBM's 15 year experiments with cosmic rays:
IBM's research on cosmic rays
I quote from this:
The cosmic ray intensity is greatest at high terrestrial altitudes, and approaches zero under extensive shielding. IBM has conducted extensive field testing3 of components at high altitudes (10,000 ft), at moderate altitudes (5000 ft), at sea level, and under shielding of 50 ft of concrete. All elevated-altitude tests showed cosmic-ray-induced fails in electronic components. In all tests, the observed fail rate scaled directly with the cosmic ray intensity, over a total observed change of more than 1000× .
There is also another related article at IBM.
IBM's research on cosmic ray densities at different places on earth
Osho
These heavily charged extremely small particles have the property that they change the capacitance of parts of semiconductors when passed through them.
Close but no cigar.
The rapid passage of a charged particle deposits enough energy on nearby charged particles to jog them out of place - creating a sudden conductive sea of electron-hole pairs. These charge carriers are then swept away by the local field, becoming a burst of current.
This affects memory and logic devices in two ways:
1) It can suddenly leak away the charge stored in the capacitance of a dynamic RAM.
2) It can momentarily turn "on" a transistor that should be off (even turning it more "on" than it normally would be, so its conduction swamps that of its turned-on partner in a totem-pole stage.)
Leaking the stored charge in a RAM flips the bit - in a particular direction. Turning on a transistor that should be off may flip a bit in a flop. latch, or static RAM, or momentarily cause the wrong level on a logic line.
Nothing to do with changed capacitance (although the sudden appearance of an extra conductive region does represent an increased capacatance on some nearby conductors).
Cosmic rays (fast charged nuclear fragments) can do this. Another problem was alpha particles from heavy elements in the ceramic integrated circuit packages once used for memory and mil-spec ICs (which is why they disappeared). A third was alpha particles from the decay of radon gas. (Turns out some locations in Silicon Valley have a lot of radon.)
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here. They even have a picture.
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Geophysics grad student actually, but I have had all the typical physics courses.
Einstein really said E = sqrt(p^2*c^2+m^2*c^4), where E = Energy, p = momentum, c = speed of light, m = rest mass. For things that are not moving this reduces to the more familiar E = mc^2.
Einstein also said, via general relativity, that gravitational fields are controlled by something known as the stress-energy tensor. In essense, it says that gravitational forces result from all energy, momentum and pressure in the universe (though mostly energy unless very high velocities are involved).
EM radiation has energy E = hv, where h is Planck's constant and v is the frequency of light. It has no rest mass (m = 0), but from above we see E = pc = hv => p = hv/c, so it has momentum. Since it has energy it creates a gravitational field, and this field would be equivalent to a particle with the same rest mass energy. [Caveat: Because momentum also contributes to the stress-energy tensor, the fields are not actually identical but the momentum correction is typically small.]
So in short a beam of gamma rays does create a gravitational field (though a very very small one for typically numbers of gamma rays).
Even though they are extemently energetic, they tend to do very little harm since:
1) The charged particle component of cosmic rays is sheilded by the Earth's magnetic field
2) The uncharged (neutron) component of cosmic rays does not interact with matter very much - it is very penetrating simpley because it passes through most matter without colliding with anything.
3) Gamma rays, like neutrons, tend to pass though quite a bit of matter without actually interacting with it.
Or more simply, we are transparent to alot of the radiation that does reach us.
Since I work for this experiment, I guess I should try to clear up a few points which have been discussed here.
A Supernova remnant (SNR) is a very rapidly expanding bubble of hot gas, created by the explosion of a massive star. It is thought that the shock wave caused by these expanding bubbles in our galaxy accelerate surrounding hydrogen gas to very high energies, which then become the cosmic ray protons which we see at the earth today. Protons form the bulk of the cosmic ray flux between MeV and EeV energies, and at least up PeV energies they seem to be formed in our Galaxy, probably by SNRs.
The SNRs are really light years across, the ones we see are generally in the local quadrant of our galaxy, thus are really not far away in the cosmic scale of things. Happily not close enough to fry us though! Cosmic redshift does not occur within our galaxy, by the way.
We detect gamma rays at very high energies by looking at their interactions with the upper atmosphere. The gamma rays themselves do not generally penetrate to the ground, we measure the Cherenkov light emitted by the shower of charged paticles which stem from the gamma ray interaction.
One reason gamma rays are interesting is that they , like other photons, travel directly to us from their source, so we can use them to make pictures of what the source looks like. We believe in this case that the gamma rays are produced in the supernova remnant by interactions of the accelerated protons, and thus are a tracer which proves the existence of the comsic rays at the SNR, and thus that SNRs generate cosmic rays.
The particles which pass through us every day are mostly muons, which are by-products of the interaction of cosmic ray protons with the atmosphere.
More information can be found at:
http://www.mpi-hd.mpg.de/hfm/HESS/HESS.html
RXJ 1713-39, the SNR in question, is believed to about 1kiloparsec away, which corresponds to 3260 light years. When we say it is believed to be 1000 years old, that means it would have been seen at the earth 1000 years ago. It is actually possibly 4000 years old, but may be older. It is quite hard to determine the distance to these things unless one saw them explode.
What we see now is 1000 years after it exploded, so we just call it 1000 years old for simplicity.
The shell should be too old and dispersed to emit gamma rays by the time it reaches the earth.
Well, you go into your neutrino detector lab, and you measure the number of neutrino interactions that you see in a certain amount of time. When you combine the known properties of the detector with the know properties of neutrinos (from other experiments that don't directly measure rates) with the rate of observed interactions, you can calculate the number of neutrinos that must have gone through the experiment without interacting in order to produce the number that DID interact. Turns out that that number is mind-bogglingly large.
That's during a severe solar flare, which is a relatively uncommon event. Otherwise, we would have a lot of dead astronauts and cosmonauts.
See http://www.asi.org/adb/m/03/11/solar-flares.html.
Mea navis aericumbens anguillis abundat
First question, yes, it is possible to do that, especially for younger SNRs (up to a few hundred years maybe). For older ones, such as RXJ 1713 its harder as its more difficult to discern expansion.
The second point refers to SN 1987a, which was observed to explode 17 years ago (hence the name).