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Astronomy, Cosmology, Physics

Magnetic Fields in Inter-cluster Space: Measured at Last

14 Apr , 2010 by

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The strength of the magnetic fields here on Earth, on the Sun, in inter-planetary space, on stars in our galaxy (the Milky Way; some of them anyway), in the interstellar medium (ISM) in our galaxy, and in the ISM of other spiral galaxies (some of them anyway) have been measured. But there have been no measurements of the strength of magnetic fields in the space between galaxies (and between clusters of galaxies; the IGM and ICM).

Up till now.

But who cares? What scientific importance does the strength of the IGM and ICM magnetic fields have?

The Large Area Telescope (LAT) on Fermi detects gamma-rays through matter (electrons) and antimatter (positrons) they produce after striking layers of tungsten. Credit: NASA/Goddard Space Flight Center Conceptual Image Lab


Estimates of these fields may provide “a clue that there was some fundamental process in the intergalactic medium that made magnetic fields,” says Ellen Zweibel, a theoretical astrophysicist at the University of Wisconsin, Madison. One “top-down” idea is that all of space was somehow left with a slight magnetic field soon after the Big Bang – around the end of inflation, Big Bang Nucleosynthesis, or decoupling of baryonic matter and radiation – and this field grew in strength as stars and galaxies amassed and amplified its intensity. Another, “bottom-up” possibility is that magnetic fields formed initially by the motion of plasma in small objects in the primordial universe, such as stars, and then propagated outward into space.

So how do you estimate the strength of a magnetic field, tens or hundreds of millions of light-years away, in regions of space a looong way from any galaxies (much less clusters of galaxies)? And how do you do this when you expect these fields to be much less than a nanoGauss (nG), perhaps as small as a femtoGauss (fG, which is a millionth of a nanoGauss)? What trick can you use??

A very neat one, one that relies on physics not directly tested in any laboratory, here on Earth, and unlikely to be so tested during the lifetime of anyone reading this today – the production of positron-electron pairs when a high energy gamma ray photon collides with an infrared or microwave one (this can’t be tested in any laboratory, today, because we can’t make gamma rays of sufficiently high energy, and even if we could, they’d collide so rarely with infrared light or microwaves we’d have to wait centuries to see such a pair produced). But blazars produce copious quantities of TeV gamma rays, and in intergalactic space microwave photons are plentiful (that’s what the cosmic microwave background – CMB – is!), and so too are far infrared ones.

MAGIC telescope (Credit: Robert Wagner)


Having been produced, the positron and electron will interact with the CMB, local magnetic fields, other electrons and positrons, etc (the details are rather messy, but were basically worked out some time ago), with the net result that observations of distant, bright sources of TeV gamma rays can set lower limits on the strength of the IGM and ICM through which they travel. Several recent papers report results of such observations, using the Fermi Gamma-Ray Space Telescope, and the MAGIC telescope.

So how strong are these magnetic fields? The various papers give different numbers, from greater than a few tenths of a femtoGauss to greater than a few femtoGauss.

“The fact that they’ve put a lower bound on magnetic fields far out in intergalactic space, not associated with any galaxy or clusters, suggests that there really was some process that acted on very wide scales throughout the universe,” Zweibel says. And that process would have occurred in the early universe, not long after the Big Bang. “These magnetic fields could not have formed recently and would have to have formed in the primordial universe,” says Ruth Durrer, a theoretical physicist at the University of Geneva.

So, perhaps we have yet one more window into the physics of the early universe; hooray!

Sources: Science News, arXiv:1004.1093, arXiv:1003.3884

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By
Hi! When I was only six (or so), I went out one clear but windy night with my uncle and peered through the eyepiece of his home-made 6" Newtonian reflector. The dazzling, shimmering, perfect globe-and-ring of Saturn entranced me, and I was hooked on astronomy, for life. Today I'm a freelance writer, and began writing for Universe Today in late 2009. Like Tammy, I do like my coffee, European strength please. Contact me: [email protected]



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Astrofiend
Member
Astrofiend
April 14, 2010 5:26 PM

Very interesting study. Magnetic fields is relative isolation are notoriously difficult to study in the universe – there are relatively few techniques available. But the field has come a long way recently, and this result is another good (if small) step forward.

Astrofiend
Member
Astrofiend
April 14, 2010 5:30 PM

>”Magnetic fields in relative isolation… “

Lawrence B. Crowell
Member
Lawrence B. Crowell
April 14, 2010 6:17 PM

Quick! Before the EU guys rubbish up this page!

A quick point about the gamma on IR/MW photon. The interaction occurs at the TeV range because there you get the electroweak interaction (g = gamma)

g + g —> Z^0 —> pions, muons etc —> e-e^+ pairs

This interaction occurs because of electroweak unification. At lower energy photons don’t interact with each other.

This is clever deduction from a measurement.

LC

IVAN3MAN_AT_LARGE
Member
IVAN3MAN_AT_LARGE
April 14, 2010 8:57 PM

@ Lawrence B. Crowell,

I, too, was going to say the same thing about ‘them’! wink

Silenus
Member
Silenus
April 15, 2010 12:04 AM

Hey, will you guys pipe down with your annoying, boring and pointless remarks about the EU guys?

People are trying to read here!

(No, I’m not one of them, it’s just very annoying having to read this same remark over en over and over again)

SteveZodiac
Member
SteveZodiac
April 15, 2010 1:38 AM

Silenus is right, this isn”t SDC. At this risk of being branded an EU follower I suspect that magnetism plays a larger role in the cosmos than it currently gets credit for. After all, most matter in the universe is actually in the form of plasma.. If magnetic fields pervade the interstellar and intergalactic medium then they must have some effect on the EM radiation passing through them – the same EM radiation which we detect and use as the basis of our cosomological theories.

Duncan Ivry
Guest
Duncan Ivry
April 15, 2010 3:39 AM

I can only support what Silenus said. We have been told again and again, that certain stupid and annoying persons will be here soon. Well, *you* are already here! My thanks go to Jean Tate for dealing with the comment policy, if you know what I mean.

DrFlimmer
Member
DrFlimmer
April 15, 2010 3:40 AM

@ SteveZodiac

If magnetic fields pervade the interstellar and intergalactic medium then they must have some effect on the EM radiation passing through them […]

Nope. Photons are not influences by magnetic fields. As is pointed out above, only secondary particles that are created in photon collisions can be used to trace magnetic fields. But radiation itself does not interact with magnetic fields!

DrFlimmer
Member
DrFlimmer
April 15, 2010 3:41 AM

(next to the comment policy we need an edit facility!)

Correction to the first sentence:

…are not influenced by….

Aodhhan
Member
Aodhhan
April 15, 2010 4:09 AM

The EU guys are just about as annoying as those who make remarks about them.
Especially if they cut and paste some non-intellectual babble which doesn’t add anything to the article.
Wait… isn’t this why they bash the EU guys?

IVAN3MAN_AT_LARGE
Member
IVAN3MAN_AT_LARGE
April 15, 2010 8:29 AM

@ Aodhhan,

May I inquire: what’s your beef with Lawrence B. Crowell? Which, I must say, is also as annoying as ‘them’.

Now, I don’t pretend to understand everything L.B.C. says and the supporting equations that he posts, but he does prompt me to look-up the subject matter on Wikipedia, Scholarpedia, and what-have-you, whenever I don’t know what the bloody hell he’s talking about — subsequently, I have learned something new and then I do know what the bloody hell he’s talking about! smile

The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
April 15, 2010 8:54 AM
@ Jean Thanks for the excellent link to Elisabete M. de Gouveia Dal Pino paper “Cosmic Magnetic Fields: from Stars and Galaxies to the Primordial Universe”. I agree this is both well balanced and explains to role of magnetic fields on various astronomical scales. I especially thought what piqued my interesting was quoting van der Hulst’s statement; “Astrophysical community with regard to cosmic magnetic fields: ”…Magnetic Fields are to Astrophysics as sex is to Psychology…”; which is now more poignant to what we have learnt in recent years is it has evolved to the proper study of “the soul” or “the mind.” In my view, this is the watershed where the extreme views fall down – as the… Read more »
The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
April 15, 2010 9:02 AM

Aodhhan said;

“The EU guys are just about as annoying as those who make remarks about them.”

Now I know I’ve absolutely been doing the right thing, here. Thanks.

There is some truth in the adage; “You teach what you most need to learn.”

You could actually learn something about yourself from that!

(All my text above was written independent of either Goggle or Wikipedia, without any “cutting or pasting” at all – in case you wanted to know.)

IVAN3MAN_AT_LARGE
Member
IVAN3MAN_AT_LARGE
April 15, 2010 9:06 AM

DrFlimmer:

But radiation itself does not interact with magnetic fields!

Au contraire, mon ami! Have you forgotten the Faraday effect?

DrFlimmer
Member
DrFlimmer
April 15, 2010 10:47 AM

@ Ivan3man

Indeed, I did, as I already noticed (but didn’t mention) after Jean Tate’s comment above. My apologies.

Lawrence B. Crowell
Member
Lawrence B. Crowell
April 15, 2010 3:52 PM
@ DrFlimmer: You are right that magnetic field do not influence photons, at least classically and for low to moderate magnetic fields. I spent a bit of time just now thinking and am wondering if this is the case for absolutely extreme magnetic fields. 10^{12}Gauss and higher B fields polarize the QED vacuum. Extreme polarizations are essentially squeezed states. This makes me ponder whether or not this could lead to nonlinear effects with radiation passing through such extreme magnetic fields. This is a quantum electrodynamics question, but classically EM radiation does not interact with magnetic fields. Sorr for the EU crack, but I just couldn’t resist @ IVAN3MAN_AT_LARGE: The faraday effect is the interaction of a charged particle… Read more »
IVAN3MAN_AT_LARGE
Member
IVAN3MAN_AT_LARGE
April 15, 2010 6:23 PM
@ Lawrence B. Crowell, On rechecking the Wikipedia reference to the Faraday effect, that I gave above, it states in the first paragraph: In physics, the Faraday effect or Faraday rotation is a magneto-optical phenomenon, or an interaction between light and magnetic field in a medium. The rotation of the plane of polarization is proportional to the intensity of the component of the applied magnetic field in the direction of the beam of light. However, in the second paragraph, it states: This effect occurs in most optically transparent dielectric materials (including liquids) when they are subject to strong magnetic fields. Furthermore, in the “Faraday rotation in the interstellar medium” section, it states: The effect is imposed on light… Read more »
IVAN3MAN_AT_LARGE
Member
IVAN3MAN_AT_LARGE
April 15, 2010 6:31 PM

P.S. Hmm… I now see that Jean Tate has also posted a clarification on magnetic fields and photons.

Anyway, this is the difference between rational, scientifically minded people, and pseudoscience cranks (mentioning no names!): the former are always self-correcting themselves with new information; the latter never admit that they were in error — no matter how trivial!

wpDiscuz