Super-tiger backgrounder: The case of the cosmic rays

Dec 27, 2012 by Diana Lutz
Super-tiger backgrounder: The case of the cosmic rays
Cosmic rays are thought to originate in nests of massive stars called OB associations, like this one in the Tarantula Nebula in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. But how did scientists figure that out? Credit: NASA, ESA, & F. PARESCE (INAF-IASF), R. O’CONNELL (U. VIRGINIA), & THE HST WFC3 SCIENCE OVERSIGHT COMMITTEE

(Phys.org)—Grade-school science teachers sometimes hand out "mystery boxes" containing ramps, barriers and a loose marble. By rotating the boxes and feeling the marble hang up or drop, the students try to deduce what's inside the box.

Physicists trying to understand why rain incessantly down from space face a similar dilemma, but their box is a hundred thousand light years across and their only clues are the particles themselves.

Just to make things more interesting, the particles don't travel in straight lines through the galaxy but instead follow tortuous paths that provide no clue to their starting point.

Naming the beasts

Given the difficulties, it is perhaps not surprising that it has taken nearly 100 years of detective work to partially solve the cosmic ray mystery. But scientists, now in hot pursuit, feel they are finally close to a complete solution.

Cosmic rays first became an object of curiosity at the turn of the century when the scientific world was agog with discoveries of different types of invisible radiation, including electrons, , and emanations from .

Scientists experimenting with the new forms of radiation quickly discovered that some high- was able to reach detectors protected by lead shielding. Where did this penetrating radiation come from? The belief spread that it was emitted by radioactive material in Earth's crust. 

That view was overturned by the Austrian scientist Victor Hess, who demonstrated, during 10 high-altitude balloon flights, that the higher one went, the more penetrating radiation one encountered. The source, then, had to be extraterrestrial (cosmic) rather than earthly.

At first the radiation was thought to be (high-energy ), which is why it was named cosmic "rays." But evidence accumulated that the rays were affected by Earth's magnetic field, which suggested the radiation consisted of charged particles instead.

Two giants of science, both Nobel laureates in physics, Robert Millikan and Arthur Holly Compton debated the issue at length, with Millikan espousing the view that cosmic rays were radiation and Compton (correctly) arguing that they were corpuscular.

Washington University has a special association with Compton. He was chair of the department of physics here from 1920-23 and awarded the Nobel Prize in Physics in 1927 for work on X-ray scattering that he did in the basement of Eads Hall at the university. He left the university in 1923 but returned here to serve as chancellor from 1945-53.

High-altitude balloons again came to the rescue, showing first that the incoming radiation consisted of protons (hydrogen nuclei) and then that there were stripped down nuclei of heavier elements among the protons.

Today we know that 90 percent of cosmic rays are hydrogen nuclei (the protons), 9 percent are helium nuclei, and the remaining 1 percent are the nuclei of heavier elements.

Most nuclei have energies between 108 and 1010 electron-volts, with the number of particles decreasing steeply at higher energies. These energies are high enough the particles zip through the galaxy at two-thirds the speed of light or faster.

Since 1962 a handful of particles with energies above 1020 electron-volts have also been spotted. These energies are so much higher than those of most cosmic rays that scientists think these extra-energtic particles must be powered by an extragalactic source, such as supermassive black hole at the center of nearby galaxy. But very little is known about them.

Tracking them to their lair

Once scientists understood what cosmic rays were, the next question was: where do they come from?

There are two parts to that question, says Martin Israel, PhD, professor of physics at Washington University and co-investigator on Super-TIGER. The first is where does all the energy come from?

"We know roughly the density of cosmic rays in the galaxy and, thanks to 'clock' nuclei among the cosmic rays, we know how long the particles wander through the galaxy before they leak out," Israel says. "Together those two measurements tell us how much energy per unit time—how much power—goes into creating cosmic rays.

"So we ask what in the galaxy is generating enough power to accelerate them, and almost certainly the only candidate is supernova explosionsthat mark the violent deaths of massive stars.

"We know how much energy is released in this type of supernova explosion and roughly how frequent the explosions are," Israel says. "And it turns out that something like 10 percent of the energy that's released in supernova explosions probably goes to accelerating cosmic rays."

The second part of the question is: where is the energy loaded onto the particles?

This time the clue is the abundance of different elements in the cosmic rays. For the most part, those abundances match the abundances of elements in the giant molecular cloud out of which the solar system condensed, called "the solar system background."

But not always. In 1997 data from ACE, a spacecraft designed to study cosmic rays and solar wind particles, showed that some isotopes are much more abundant in the cosmic rays than in the solar system background.

Super-tiger backgrounder: The case of the cosmic rays
Victor Hess in the basket of one of his balloons in about 1911. The crowd of enthusiastic science groupies is usually cropped out of reproductions of the photo.

"The one that's far and away the outlier is the ratio of neon 22 to neon 20," says W. Robert Binns, PhD, research professor of physics and Super-TIGER principal investigator. "That turned out to be five times higher in the cosmic rays than in the solar system background, and that's a huge difference."

The abundance of neon 22 raised eyebrows because nucleosynthesis calculations and astronomical observations show it is produced copiously by Wolf-Rayet stars, a spectacular stage in the evolution of stars born with a mass greater than about 30 solar masses.

During the Wolf-Rayet stage, the stars shine so brightly the force of the light pushing outward sets up fierce stellar winds that scour the surface of the star, carrying off an Earth's-worth of material in as little as a year.

"In the winds from Wolf-Rayet Stars there's lots of neon 22," say Binns. "So once it was understood that neon 22 was overabundant in cosmic rays, it seemly likely the Wolf-Rayet stars were contributing to them.

"We couldn't account for our data," says Binns, "unless we assumed cosmic rays had two sources. One component is ordinary solar system background material, just the everyday dust and gas that's lying around out there. The other component is material from the Wolf-Rayet stars."

To make the numbers work, the physicists found they had to add two parts Wolf-Rayet material to eight parts interstellar medium.

At this point, the bigger picture was beginning to emerge. "The thing about Wolf-Rayet stars," Binns says, "is they're almost all found in loosely organized groups of hot, massive stars called OB associations."

Super-tiger backgrounder: The case of the cosmic rays
The Crescent Nebula in the constellation Cygnus was created by strong winds blowing outward from the Wolf-Rayet star at its center. The powerful high-velocity winds driven by the star’s intense luminosity can sweep the equivalent of the Earth’s mass off the star’s surface every year. Scientists think that some cosmic rays are Wolf-Rayet wind material. Credit: J-P METSAVAINIO (ASTRO ANARCHY)

These are clusters of stars that formed from a single interstellar cloud and are drifting together through space. Ninety percent of stars are thought to have formed in stellar associations, of which there are three types distinguished by properties of the stars they harbor.

The most massive stars are born in OB associations consisting of 10 to a few hundred stars of spectral types O and B (both massive, blue stars). High-velocity winds from the stars and supernovae explosions as they reach the ends of their short lives blow enormous cavities in the interstellar medium, from which the remaining stars shine boldly forth.

It was beginning to look like the scientists had nailed the evidence and sealed the case. The winds from the Wolf-Rayet stars were seeding the interstellar medium in OB associations with exotic isotopes which were then swept up and accelerated, together with regular solar system material, by volleys of supernovae explosions.

A mini-mystery

There is another small piece of the puzzle that both Binns and Israel bring up, in part because it is such a neat example of the methods of cosmic-ray science.

The question was: are cosmic rays stuff that was made and expelled in a supernova explosion? Or are cosmic rays stuff that was made in a supernova, spewn out into the interstellar medium, and then accelerated a million years later by the shock wave from another supernova?

And how could you possibly tell which scenario is accurate?

It turns out that nickel isotopes give the answer. Most of the nickel found in nature is in the form of two stable isotopes: nickel 58 and nickel 60. Nickel 59, however, is radioactive and not stable.

Importantly nickel 59 decays by capturing one of its own electrons, which converts a proton to a neutron, turning nickel 59 into cobalt 59.

But cosmic rays are bare nuclei, stripped of their electrons when they are accelerated to cosmic ray energies. So once nickel 59 has been accelerated, it's a stable nucleus that will last more or less indefinitely.

If nickel 59 is made in supernova explosions and accelerated promptly to cosmic ray energies, it should show up in cosmic rays. If, on the other hand, it is made in a supernova explosions and then lies around in the interstellar medium for a few million years it shouldn't be found in the cosmic rays.

Neither TIGER nor Super-TIGER can identify isotopes, but they are being measured by the CRIS instrument on the ACE. CRIS, like Super-TIGER a collaboration among Washington University, the CAlifornia Institute of Technology and NASA's Goddard Space Flight Center, was launched into orbit in 1997.

"I can show you out in the hall the ACE histogram of nickel isotopes," Israel says.

We go to look. There's a nice peak at nickel 58 and a nice peak at nickel 60 and nothing in between. In the histogram of cobalt isotopes, the missing nickel 59 reappears as cobalt 59.

"The math all works," says Binss. 'Nickel 59 has a half-life of about 76,000 years and supernova go off in OB associations roughly once every million years, so there's ample time for the nickel to decay before being accelerated."

What Super-TIGER is stalking

If scientists are pretty sure they know where cosmic rays come from, why is a WUSTL-led team currently in Antarctica lofting a two-ton instrument the size of a pool table into the polar vortex to catch more cosmic rays? What is the Super-TIGER experiment looking for?

If scientists could just order the data they wanted from a catalog, they'd ask for the abundances of all of the naturally occurring elements in the periodic table and all of their isotopes.

But when they go into the field to collect cosmic rays, this is not what they get. Out of every 100 cosmic rays they intercept, only 1 will be the nucleus of an element heavier than helium.

But most of the information about cosmic-ray origins has been gleaned from that 1 percent. So the most desirable quarry is also the most elusive quarry.

Even though Super-TIGER's predecessor, TIGER, flew for a record-breaking 31.5 days in 2001, its detector was struck by only about 300 particles of the elements between zinc and zirconium.

That's only about 10 particles per element, which didn't give the scientists a very good measure of their relative abundance. "Look at the size of those error bars," Binns says pointing to a graph of the data with a grimace of chagrin.

Super-TIGER, which is much bigger than TIGER, should catch nearly eight times cosmic rays, if it can only stay up as long. That would give the scientists much better "statistics."

"You'll also notice," says Israel, "that when I talk about supernova blasts accelerating the particles I'm waving my arms a lot."

While scientists are nearly certain supernova blasts are the acceleration engine, nobody is sure exactly how this works. But Binns and Israel think a clue is beginning to emerge from the cosmic ray data.

It has to do with gas and dust. There isn't much of anything in space, but it isn't empty. There is a little gas—about one gas atom per cubic centimeter –and a sprinkle of dust—not dust as in dust bunnies but tiny grains of stuff like sand or ice.

The data are suggesting that when the interstellar medium is accelerated, the dust somehow gets the jump on the gas. An acceleration mechanism that would make this distinction has been proposed. It predicts that heavier volatiles (the gas) should have higher cosmic-ray/ solar system ratios than lighter ones, but that the refractories (the dust) would not display mass dependence.

"However, our TIGER data indicate similar (but not identical) mass dependence for both the volatiles and refractories," says Israel. "So one of the main things we are looking for with Super-TIGER is improved statistics for the heaviest elements, so that we can pin down the refractory mass-dependence."

Victor Hess would have understood. When he went up in his balloons to measure , he was repeating an earlier experiment. In 1919 Theordor Wulf, a German scientist, had carried a detector to the top of the Eiffel Tower in Paris and found that radiation decreased rather than increased as he ascended.

Hess ascended to 17,000 feet, more than 30 times higher than the Eiffel tower is tall because he suspected that better statistics were needed. He was right.

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Caliban
3 / 5 (2) Dec 27, 2012
What about the possibility of at least part of these cosmic ray's origin and acceleration being caused by BH polar jets?

Seems like a pretty fair prospect as cause for at least a portion.
cantdrive85
1 / 5 (11) Dec 27, 2012
It has to do with gas and dust. There isn't much of anything in space, but it isn't empty. There is a little gas—about one gas atom per cubic centimeter –and a sprinkle of dust—not dust as in dust bunnies but tiny grains of stuff like sand or ice.


There is in fact ZERO gas in space, it's 100% plasma. Something that astrophysicists don't want to admit to due to the complexity of the applicable models, at some point they will have to admit this fact, when they do they'll have to find new metaphysics to research.
LED Guy
5 / 5 (6) Dec 27, 2012
@cantdrive - are you saying that the neutral hydrogen detected by radio telescopes isn't a gas? That it's a plasma?

Wow, who knew that you could have a neutral plasma????

Oh yeah, neutral plasmas are called gases - lol
cantdrive85
1 / 5 (9) Dec 27, 2012
That "neutral" hydrogen has been found to be plasma, even NASA will acknowledge this.

http://public.lan...APSS.pdf
http://public.lan...tAsJ.pdf
http://public.lan...2000.pdf

One of the elementary characteristics of plasma is the prodigious amounts of EM radiation they produce, this is why the non-visible wavelengths of astronomy is so vital to observation being that >99.9% of the Universe is plasma.
Caliban
5 / 5 (7) Dec 28, 2012
That "neutral" hydrogen has been found to be plasma, even NASA will acknowledge this.

http://public.lan...APSS.pdf

One of the elementary characteristics of plasma is the prodigious amounts of EM radiation they produce, this is why the non-visible wavelengths of astronomy is so vital to observation being that >99.9% of the Universe is plasma.


Get a grip, cd.

These papers all cross reference each other, and are merely hypothesis and speculation regarding observed effects in hydrogen filaments.

No claim is made --much less by NASA, as you assert-- that ALL interstellar hydrogen is plasma.

You continually resort to the worst sort of wishful thinking and hyperbole, and grasp at ANY reseasrch that could IN ANY WAY be distorted or misinterpreted to support your pet theory.

This monomania of yours has gotten really, really tiresome.

You don't own the Secret of the Ages.


cantdrive85
1 / 5 (7) Dec 28, 2012
If it's not plasma, why does it behave as a plasma should? The filaments you describe does NOT happen with gas, that is a plasma characteristic. No matter what wishful thinking you like to resort to, gas does not form self organizing filamentary and cellular morphology, nor does it emit high energy synchotron radiation or create MAGNETIC FIELDS. According to most of you fools, if it looks like a duck, walks like a duck, and quacks like a duck, it must be leprechaun.
If it is ionized one billionth of a percent, it will behave as a plasma and will be driven by the EM force and gravity's affect will be negligible.
The fact that those "neutral" hydrogen clouds have all the characteristics of plasma (filamentary, cellular, magnetized, emit synchotron rad., etc...) to claim it is gas is wishful thinking at best, but I think willful ignorance is more likely.
Q-Star
4.2 / 5 (10) Dec 29, 2012
There is in fact ZERO gas in space, it's 100% plasma. Something that astrophysicists don't want to admit to due to the complexity of the applicable models,


cantdrive, please be a little more tolerant of the astrophysicists, after all, their silly models are attempting to incorporate so much into so little.

Unlike the plasmatists, who only need PLASMA to do their work, they are trying to explain thermodynamics, gravity, electromagnetics, quantum mechanics, chemistry, nuclear physics, particle physics, fluid dynamics, classical mechanics, and a lot of other stuff to explain reality.

If all you need to study and account for is plasma, then your work is easy, probably not very good for a COMPLETE explanation of the universe, but it is easy.

Why study calculus if you already know how to add 2 plus 2? Right?
stetrekve
5 / 5 (1) Dec 29, 2012
per the article: "Ninety percent of stars are thought to have formed in stellar associations, of which there are three types distinguished by properties of the stars they harbor."

Is our Sun a part of a stellar association and , if so, what are the other stars that are in the array? Alpha Cent? Vega?

Steve
antialias_physorg
5 / 5 (5) Dec 29, 2012
Is our Sun a part of a stellar association and , if so, what are the other stars that are in the array? Alpha Cent? Vega?

Since our sun is a couple of billion years old (which comes out to several dozen galactic revolutions) the association it was part of are probably spread all over the place by now.

Best bet for finding our 'sibling stars' would be to look for starts with a similar composition (adjusted for size) and age as ours.
LED Guy
4 / 5 (4) Dec 29, 2012
@Cantdrive:

If you're not an idiot, why do you behave like one?

Your logic fails on so many levels. You yourself admit that plasmas are charged, yet you try to claim that neutral hydrogen (a non-ionized hydrogen molecule) is a plasma. Is air a plasma too????
cantdrive85
1.6 / 5 (7) Dec 29, 2012
@Cantdrive:

If you're not an idiot, why do you behave like one?

Your logic fails on so many levels. You yourself admit that plasmas are charged, yet you try to claim that neutral hydrogen (a non-ionized hydrogen molecule) is a plasma. Is air a plasma too????


If you notice, I inserted quotation mark around "neutral", I've been told on these comment boards that when you do that whatever is between the quotes can mean whatever I choose it to be. In this instance, "neutral" is by name only, not the actual physical condition of the "hot gas". Astronomers and astrophysicists call these clouds of neutral hydrogen, but they behave as if they are plasma, as noted above, I call them "neutral" because they are not neutral, they are ionized.

Greenwood
5 / 5 (4) Dec 29, 2012
Cantdrive you claim that gas can't show the filamentation seen there because you claim that none of the formations that do are gas, see any cyclical logic here? The real question is how would plasma emit the neutral hydrogen line?
cantdrive85
1.6 / 5 (7) Dec 30, 2012
Cantdrive you claim that gas can't show the filamentation seen there because you claim that none of the formations that do are gas, see any cyclical logic here? The real question is how would plasma emit the neutral hydrogen line?

Mr. Vershuur discusses this issue in his papers. In addition to that;
"The term plasma also includes ionized gas at relatively low temperature, where only some of the atoms or molecules have lost electrons" Peratt

LED Guy- Is air a plasma too????

This from Peratt as well;
"As a thunderstorm develops, negative charges build along the cloud base, causing positive charges to build up on the ground below. The resulting electric field between the two concentrations becomes so strong that it ionizes the air. This creates a conducting path for free electrons and ions - a plasma - through which lightning discharges."
So I guess the answer is yes in certain situations.
cantdrive85
1.4 / 5 (10) Dec 30, 2012
Q, being that over 99.9% of the stuff astrophysicists and astronomers observe and study is plasma, it is vital they become plasmatists. A lot of that "other stuff" that they use to explain reality has zero bearing on what they study and it does nothing but clutter their mind from seeing what would otherwise be obvious.
jsdarkdestruction
3.4 / 5 (5) Dec 30, 2012
"it is vital they become plasmatists"
cantdrive, their are many many talented scientists working on plasma. Why dont you go to them and peddle your ideas? oh yeah, you would laughed right out the door.
Lurker2358
1 / 5 (3) Dec 30, 2012
But cosmic rays are bare nuclei, stripped of their electrons when they are accelerated to cosmic ray energies. So once nickel 59 has been accelerated, it's a stable nucleus that will last more or less indefinitely.


Ridiculous fallacy.

For all you know, the nickel 59 could have collided with an electron at some point during the acceleration, or afterwards, and then decayed to Cobalt that way.

Temperature and kinetic energy of forward motion are not exactly the same thing.
Widdekind
1.8 / 5 (5) Dec 31, 2012
Or are cosmic rays stuff that was made in a supernova, spewn out into the interstellar medium, and then accelerated a million years later by the shock wave from another supernova?


CRs are enriched in Neon-22 (stable) and Cobalt-59 (decays from Nickel-59 in ~100Kyr), both of which derive from regions around massive stars (OB associations). Short-lived isotopes are not accelerated into CRs. But long-lived isotopes, persisting for ~1Myr until the next SN explosion, are accelerated into CRs. So, there seems to be a parallel, between CRs, and galaxy winds. In both cases, particles are accelerated out of their parent SN, only to be multiply re-accelerated, by subsequent SN. Ipso facto, CRs streaming through our galaxy could be construed as an "intra-galactic galaxy wind". CRs blown out in other directions would become our galaxy's "galaxy wind". The parallel process, in distant galaxies, could account for extra-galactic CRs, detected at earth.
Fleetfoot
5 / 5 (4) Dec 31, 2012
But cosmic rays are bare nuclei, stripped of their electrons when they are accelerated to cosmic ray energies. So once nickel 59 has been accelerated, it's a stable nucleus that will last more or less indefinitely.


Ridiculous fallacy.

For all you know, the nickel 59 could have collided with an electron at some point during the acceleration, or afterwards, and then decayed to Cobalt that way.


The nuclei are moving at high speed relative to the ISM so any such collision would result in a relativistic electron rebounding and a slight reduction in the speed of the cobalt ion. The electron would have a very low probability of capture until the speed fell considerably. The same mechanism would also mean that the other species would also arrive at low velocities, but that is not what is observed.
Widdekind
1 / 5 (3) Jan 01, 2013
Could not Nickel-59 decay by positron emission (inverse beta decay) ? If so, then perhaps the longevity of Nickel-59 would derive from relativistic speeds & time dilation ?
VendicarD
5 / 5 (2) Jan 01, 2013
Your understanding of the subject would help if you actually knew what plasma was. I presume you already know what the definition of "Neutral" is..

"That "neutral" hydrogen has been found to be plasma, even NASA will acknowledge this." - CantDrive
cantdrive85
1 / 5 (6) Jan 01, 2013
"The term plasma also includes ionized gas at relatively low temperature, where only some of the atoms or molecules have lost electrons" Peratt

So... You're suggesting that there are zero free electrons or ions in "neutral" hydrogen clouds. Pretty much flies in the face of the evidence.
Fleetfoot
5 / 5 (3) Jan 01, 2013
Could not Nickel-59 decay by positron emission (inverse beta decay)?


Wouldn't that require the presence of an electron antineutrino? The usual decay mode is electron capture which can't happen if there are no electrons.

http://en.wikiped...ta_Decay

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