Swirling electrons in the whirlpool galaxy

Aug 20, 2014
LOFAR radio map of the whirlpool galaxy M51 and its neighbourhood at a frequency of 150 MHz. The field covers 4 by 2.6 degrees. The observations were performed with the Dutch LOFAR high-band antennas. The map shows the distribution of hot electrons in M51 and also a large number of background galaxies.The inlay shows an enlarged view of M51 at 150 MHz (white contour lines) overlayed onto an optical image of M51 from the Digital Sky Survey (DSS). Credit: © David Mulcahy et al., Astronomy & Astrophysics

The whirlpool galaxy Messier 51 (M51) is seen from a distance of approximately 30 million light years. This galaxy appears almost face-on and displays a beautiful system of spiral arms.

A European team of astronomers was able to observe M51 with the International LOFAR Telescope in the frequency range 115-175 MHz, just above the normal commercial FM radio frequency band of 88-108 MHz. The team obtained the most sensitive image of any galaxy at frequencies below 1 GHz so far.

With LOFAR's high sensitivity, the disk of M51 in the radio regime could be traced much further out than before. The astronomers detected cosmic electrons and magnetic fields 40,000 light years away from the center of M51. With LOFAR's high angular resolution, the are clearly visible. Magnetic fields and cosmic rays are densest in spiral arms. Compared to higher radio frequencies, spiral arms appear broader due to the diffusion of cosmic electrons away from the spiral arms where they have been formed.

The view of galaxies in the radio regime is different to their optical appearance. Whereas optical images show predominantly the visible light from stars, the unravel two constituents of galaxies that are invisible to optical telescopes: electrons, almost as fast as light, and magnetic fields. Their role for the stability and evolution of galaxies is increasingly under discussion. The electrons are "cosmic ray" particles produced in the shock fronts of giant supernova explosions. Magnetic fields are generated by dynamo processes driven by gas motions. When the electrons spiral around the magnetic field lines, radio waves are emitted, a process called synchrotron emission. Its intensity increases with the number and energy of the electrons and with strength.

For many decades, radio astronomy has been unable to explore low frequencies below 300 MHz because the ionosphere acts as a barrier of low-frequency radio waves (which are completely blocked below about 10 MHz). Sophisticated methods of data processing and superfast computers are needed to recover the emission. Due to these technical challenges, spiral galaxies have hardly been studied before at these very low radio frequencies. The only observations were of poor resolution and no details could be made out.

LOFAR Stations in Europe. Credit: © ASTRON, The Netherlands

The target of investigation in David Mulcahy's PhD project was the beautiful spiral galaxy Messier 51 at a distance of about 30 million light years which is visible already in a small telescope in the constellation "Canes Venatici", not far away from the famous Big Dipper (in German: "Großer Wagen") in the sky.

"Low-frequency radio waves are important as they carry information about electrons of relatively low energies that are able to propagate further away from their places of origin in the star-forming spiral arms and are able to illuminate the magnetic fields in the outer parts of galaxies", says David Mulcahy. "We need to know whether magnetic fields are expelled from galaxies and what their strength is out there."

"This beautiful image, coupled with the important scientific result it represents, illustrates the fantastic advances that can be made at low radio frequencies with the LOFAR telescope", continues Anna Scaife from Southampton University, co-author of the paper. "Unravelling the mysteries of magnetic fields is crucial to understanding how our Universe works. For too long, many of the big questions about magnetic fields have simply been untestable and this new era of radio astronomy is very exciting."

The Low Frequency Array (LOFAR), designed and constructed by ASTRON in the Netherlands, is a brand new radio telescope giving access to very low radio frequencies.

LOFAR explores the relatively unexplored frequency range below 240 MHz and consists of a multitude of small and simple antennas without moving parts. LOFAR consists of 38 stations in the Netherlands, 6 stations in Germany and one station each in the UK, France and Sweden. The novelty is the online combination of the signals from all stations in a powerful computing cluster located at the University of Groningen (Netherlands).

Observations of M51 with LOFAR below FM (at 30-80 MHz) have already taken place. "This opens a new window to the Universe where we do not know how galaxies will look like", concludes Rainer Beck, who supervised David Mulcahy's PhD project. "Maybe we will see how galaxies are magnetically connected to intergalactic space. This is a key experiment in preparation for the planned Square Kilometre Array (SKA) that should tell us how cosmic magnetic fields are generated."

Explore further: Triangulum galaxy snapped by VST

More information: The nature of the low-frequency emission of M51: First observations of a nearby galaxy with LOFAR, by D.D. Mulcahy, A. Horneffer, R. Beck et al., 2014, Astronomy & Astrophysics , DOI: 10.1051/0004-6361/201424187

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User comments : 22

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Shootist
5 / 5 (6) Aug 20, 2014
The Electric Universe!®©
cantdrive85
1.1 / 5 (9) Aug 20, 2014
Their role for the stability and evolution of galaxies is increasingly under discussion.

Ummm, nice of them to finally get around to that considering Alfven's prediction of galactic magnetic fields over 75 years ago.

Due to these technical challenges, spiral galaxies have hardly been studied before at these very low radio frequencies. The only observations were of poor resolution and no details could be made out.

Yet it doesn't prevent many from making claims the large scale magnetic fields are of little concern.

says David Mulcahy. "We need to know whether magnetic fields are expelled from galaxies and what their strength is out there."

One more time, magnetic fields cannot exist w/o an electric current, as such they cannot be "expelled from galaxies".

"...For too long, many of the big questions about magnetic fields have simply been untestable and this new era of radio astronomy is very exciting."

That's why Plasma Cosmologists base their theories upon laboratory research...
cantdrive85
1.3 / 5 (8) Aug 20, 2014
that should tell us how cosmic magnetic fields are generated."


Then again, we can refer to the 300+ years of research into EM and understand they are created just like they are here on Earth, electricity.
Elmo_McGillicutty
1 / 5 (3) Aug 21, 2014
Angular momentum is the father the magnetism. Galaxies are nothing but specks of light on huge magnetic circuits. This circuit goes thru the center and is powered by the galactic rotation. Bubbles anyone?
FineStructureConstant
5 / 5 (3) Aug 21, 2014
Bubbles anyone?
- don't mind if I do! Pass me one of those cream puffs while you're at it.
FineStructureConstant
5 / 5 (10) Aug 21, 2014
One more time, magnetic fields cannot exist w/o an electric current
- damn! Will somebody show me the off-switch on this refrigerator-door magnet?
Whydening Gyre
4.5 / 5 (4) Aug 21, 2014
One more time, magnetic fields cannot exist w/o an electric current, as such they cannot be "expelled from galaxies".

Other way 'round. Electricity is a result of magnetic interaction.
Magnet's first, electricity second.
cantdrive85
1 / 5 (4) Aug 21, 2014
One more time, magnetic fields cannot exist w/o an electric current, as such they cannot be "expelled from galaxies".

Other way 'round. Electricity is a result of magnetic interaction.
Magnet's first, electricity second.

Make sure you tell Maxwell, experiment be damned.
Whydening Gyre
5 / 5 (3) Aug 21, 2014
Make sure you tell Maxwell, experiment be damned.

To put it in another way - electricity is the "carrier" of magnetic info. Magnet's don't carry electricity. Without a kinetic differential between magnetic fields, there would be no "info" for electricity to carry.
Kinda like your plasma double layer thing....
Anyway, I can't - he's dead.
Whydening Gyre
5 / 5 (1) Aug 21, 2014
Angular momentum is the father the magnetism.

And another - other way around....
Da Schneib
4.2 / 5 (5) Aug 21, 2014
Errrr, actually magnetism is the relativistic correction for the speed-of-light propagation of the electric field. That's why it always works at right angles to the electric field. It's also why you never find a magnetic field without an electric field.
FineStructureConstant
5 / 5 (6) Aug 22, 2014
magnetism is the relativistic correction for the speed-of-light propagation of the electric field. That's why it always works at right angles to the electric field. It's also why you never find a magnetic field without an electric field.
- there's a man who knows his stuff. It's all in the field, people.

That's why Plasma Cosmologists base their theories upon laboratory research
Extrapolation of test-tube studies which - by their very nature - ignore gravity, quantum mechanics, relativity, nuclear physics AND MATH are just not going to hack it in the big wide universe out there. Such theories only work in the blinkered minds of those adherents of lame "theories" proposed half a century and more ago, by engineers who simply could not understand mainstream astrophysics of the day. They'd be even more lost today. That's why they were ignored then by the mainstream, and why they and their followers continue to be ignored, regardless of the amount of noise they make.
Whydening Gyre
5 / 5 (2) Aug 22, 2014
Errrr, actually magnetism is the relativistic correction for the speed-of-light propagation of the electric field. That's why it always works at right angles to the electric field. It's also why you never find a magnetic field without an electric field.

Thanks, The Da, but you're gonna have to lay that out a little a little simpler for me. I'm not able to visualize what you are saying...(it's a slow day)
Captain Stumpy
5 / 5 (5) Aug 23, 2014
Extrapolation of test-tube studies which - by their very nature - ignore gravity, quantum mechanics, relativity, nuclear physics AND MATH are just not going to hack it in the big wide universe out there. Such theories only work in the blinkered minds of those adherents of lame "theories" proposed half a century and more ago, by engineers who simply could not understand mainstream astrophysics of the day. They'd be even more lost today. That's why they were ignored then by the mainstream, and why they and their followers continue to be ignored, regardless of the amount of noise they make.
@FineStructureConstant
Thank you for being so clear and concise. I've been trying to get this point across to cd for ages... I bet he STILL ignores it though...

p.s. "...you use your tongue prettier than a twenty dollar whore" (Blazing Saddles)
http://www.moviem...4/quotes
cantdrive85
1 / 5 (3) Aug 23, 2014
Extrapolation of test-tube studies which - by their very nature - ignore gravity, quantum mechanics, relativity, nuclear physics AND MATH


To take one from Cap'n Stupid's typical blather;
Personal conjecture base upon ignorance of the physics involved.

Oh, and Cap'n Stupid, before you roll out the usual blog based drivel of Timmy Thompson, why don't you PROVE IT...
FineStructureConstant
5 / 5 (3) Aug 23, 2014
Personal conjecture base upon ignorance of the physics involved.
- dream on, boot-boy.
no fate
2 / 5 (1) Aug 25, 2014
Errrr, actually magnetism is the relativistic correction for the speed-of-light propagation of the electric field. That's why it always works at right angles to the electric field. It's also why you never find a magnetic field without an electric field.


Other than that fridge magnet with no off switch mentioned above. And as WG says, "lay that one out for me"... specifically what the term relativistic correction applies to. Electric current is a quantum phenomenon already so there is no requirement for a transformation from classical physics or "relativistic correction". It may help if somewhere on earth the term relativistic correction was defined stating what exactly you are doing when you calculate it.
cantdrive85
1 / 5 (2) Aug 31, 2014
Errrr, actually magnetism is the relativistic correction for the speed-of-light propagation of the electric field. That's why it always works at right angles to the electric field. It's also why you never find a magnetic field without an electric field.


Magnetic and electric fields can be aligned, such as in a field aligned current (Birkeland currents). As such, your statement and explanation is false.
Da Schneib
5 / 5 (1) Sep 12, 2014
Thanks, The Da, but you're gonna have to lay that out a little a little simpler for me. I'm not able to visualize what you are saying...(it's a slow day)
OK.

If you are in the same frame with an electron and it is held motionless with respect to you, and a proton flies by near it but doesn't touch it, then the proton first approaches the closest point, then recedes from it. Now, the force from the proton acts, but only at the speed of light; so the electron isn't attracted to where the proton IS, but where it WAS. As you know, forces can be separated into components, and added together to get the original force. In this case, the two components are the direct action of the electrical force, and the action *introduced by the speed of light delay, which pulls the electron at right angles to the direct electric force and along the line of motion of the proton*.
contd
Da Schneib
not rated yet Sep 12, 2014
The first action, we call the electric force; the second, which acts always at right angles to the electric force and always in the opposite of the direction of motion of the proton, we call the magnetic force.
Da Schneib
not rated yet Sep 12, 2014
Errrr, actually magnetism is the relativistic correction for the speed-of-light propagation of the electric field. That's why it always works at right angles to the electric field. It's also why you never find a magnetic field without an electric field.
Other than that fridge magnet with no off switch mentioned above.
Actually the electrons in their orbitals appear to move around in a circle from far away, and this motion causes speed-of-light delayed effects on other charged particles such as electrons and protons in the other magnet or in the iron attracted by the magnet. If you know a way to make electrons stop moving around the nucleus that's your "off switch." Nobody knows how to do that other than drop the magnet onto a neutron star or into a black hole.

specifically what the term relativistic correction applies to.
The speed-of-light delay.
Da Schneib
not rated yet Sep 12, 2014
One more time, magnetic fields cannot exist w/o an electric current
- damn! Will somebody show me the off-switch on this refrigerator-door magnet?
Naughty. It's the electrons revolving in their orbitals that make the electric current. You know that. ;)