APOD: Spiral Galaxy M96 from Hubble (2015 Sep 21)

[Ann]

sallyseaver wrote:
And IF iron is a strong component of the brown dust clouds in our APOD picture of M96, then in cold space the microscopic domains would line up to have a macroscopic magnetic field that would influence its interaction with the other constituents of the outer ring of M96.

Oh, you are talking about magnetism!

Yes, astronomers are "upgrading" magnetism as a major player in the universe, or so I believe anyway. But personally I doubt that magnetism would normally give a galaxy a distorted shape. As for that dust lane of M96, you are of course correct that it contains iron as well as other elements. I'm sure the iron content is enough for this dust lane to "feel" the magnetic field of the galaxy.

But I don't see why this particular dust lane would be extremely rich in iron. The only thing that could make it so is if it was made of the debris of vast numbers of particularly metal-rich stars. I don't see why that would be the case, and why, say, Andromeda would not have dust lanes even richer in iron. Andromeda is larger than M96 and redder in overall color, suggesting it contains a larger population of very metal-rich stars. Also, when it comes to M96, I'm having a hard time imagining the sort of magnetic field that would have such a "lopsided" effect on the galaxy.

The universe is teeming with strangely shaped galaxies. I find it hard to believe that magnetism is acting on some parts on them and not on other parts, or that it affects some parts of the galaxies much more strongly than other parts. Why would that be?

We know that mergers give galaxies strange shapes. We also know that massive star formation in a galaxy can distort the entire galaxy. For example, galaxy NGC 1313 is distorted due to massive star formation primarily taking part in one of its arms. There is nothing strange about that. Star formation is always a localized phenomenon, never something that envelops an entire galaxy - certainly not in the nearby universe.

As for M96, I agree with Chris that a merger is by far the most likely explanation for its weird shape.

Ann

[Chris Peterson]

Chris, you said to be cautious about trying to infer 3D structure, but you can see the light from the middle of 96M shining through the swath of dust...

Maybe we can, maybe not. The intensity range seen in a galaxy has much greater dynamic range than our displays are capable of showing. So galaxy images are almost always processed in a way that modifies the actual intensity relationships. To really understand these kinds of images, we need to go back to the raw data.

Where does the original angular momentum come from? My understanding is that the original matter started like the big nebulae we see in other parts of the cosmos, like The Great Nebula (APOD Jan 19, 2015) or Gamma Cygni Nebula (APOD April 22, 2015) or the Carina Nebula. [from Big Bang TO stars TO the nebula material after stars die, i.e. planetary nebulae] Then if matter accretes around a denser part of the big nebula, it seems to me that the accretion would tend to be spherical. How does the angular momentum get started according to current thinking?

We don't know what galaxies formed out of, we don't really know how star formation and galaxy formation were connected, or what order they occurred in. But assuming that a galaxy formed out of something that can be thought of as a "nebula", meaning a vast region of somewhat condensed material, then the angular momentum is simply the net angular momentum of that material, which certainly would not be zero. As the huge "nebula" condensed, the rotational speed increased (because of conservation of angular momentum).

Accretion is only spherical if the material doesn't interact like a fluid, or if the angular momentum is very low. At high densities, however, that's exactly how it behaves.

IF there is a dust prominence in the absence of interacting with a different galaxy, then it could mean that the dust is primarily iron (an abundant element) with it's own magnetic properties so that it does not interact in the same way as the other orbital material?

Iron is a trace component in interstellar dust. However, dust need not be composed of ferromagnetic material to be influenced by magnetic fields.

[neufer]

[b][color=#0000FF]Optical image of the spiral galaxy M 51 obtained with the Hubble Space Telescope, overlaid by contours of the total radio intensity and polarization vectors at 6cm wavelength, combined from radio observations with the Effelsberg and VLA radio telescopes. The magnetic field follows well the optical spiral structure, but the regions between the spiral arms also contain strong and ordered fields. Copyright: MPIfR Bonn[/color][/b]

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IF there is a dust prominence in the absence of interacting with a different galaxy, then it could mean that the dust is primarily iron (an abundant element) with it's own magnetic properties so that it does not interact in the same way as the other orbital material?

Iron is a trace component in interstellar dust. However, dust need not be composed of ferromagnetic material to be influenced by magnetic fields.

But is dust dynamically influenced by magnetic fields
(other than simply having its dipole reoriented)

Galactic magnetic fields by Dr. Rainer Beck,
Max-Planck-Institut für Radioastronomie, Bonn, Germany

<<Galactic magnetic fields can be observed in the optical range via starlight which is polarized by interstellar dust grains in the foreground. These grains are elongated and can be aligned by magnetic fields, where the major axis becomes perpendicular to the field lines. Measurements of many stars revealed a general picture of the magnetic field in the Milky Way near the Sun. Aligned dust grains also emit polarized infrared emission, which is very useful to show magnetic fields in dust clouds in the Milky Way. In prominent spiral arms the field strength can be up to 25 μG, in regions where also cold gas and dust are concentrated.>>

[Ann]

Interesting image, Art. The magnetic field of M51 appears to follow the dusty features pretty well. Could it be that large dust patches are typically more magnetized than relatively dust-free zones? Could it be that the strange dust lane of M96 really has a stronger magnetic field that its relatively dust-less yellow surroundings?

But if so, I would certainly guess that it wasn't magnetism that created that dust lane out of nothing, so to speak, but rather that an external factor such as a merger gave rise to the dust lane, and at the same time the violence of the merger created new centers of magnetism in the galaxy. Now, hundreds of millions of years after the merger, the lopsided dust lane of M96 might still carry the imprint of the magnetism that resulted from the merger.

But that would make the magnetism involved a consequence and not a cause of that dust lane.

Ann

[FullMoon]

What a mesmerizing galaxy. Taken by the ol' Hubble, too.
While I don't know much about this particular galaxy, I've always found the outer universe intriguing. Perhaps someday we'll be able to explore it with our own eyes.

[geckzilla]

What a mesmerizing galaxy. Taken by the ol' Hubble, too.
While I don't know much about this particular galaxy, I've always found the outer universe intriguing. Perhaps someday we'll be able to explore it with our own eyes.

We are exploring it with our own eyes, augmented by cameras! Without some kind of camera to aid us, our own eyes... well, I'd liken it to say we can fly about as well as a bird with our own arms as we can see the Universe with our own eyes.

[starsurfer]

What a mesmerizing galaxy. Taken by the ol' Hubble, too.
While I don't know much about this particular galaxy, I've always found the outer universe intriguing. Perhaps someday we'll be able to explore it with our own eyes.

We are exploring it with our own eyes, augmented by cameras! Without some kind of camera to aid us, our own eyes... well, I'd liken it to say we can fly about as well as a bird with our own arms as we can see the Universe with our own eyes.

I wonder what Superman's x-ray vision of the universe would be like?

[neufer]

I wonder what Superman's x-ray vision of the universe would be like?

• . http://www.xray.mpe.mpg.de/cgi-bin/rosat/rosat-survey

[Ann]

I wonder what Superman's x-ray vision of the universe would be like?

• . http://www.xray.mpe.mpg.de/cgi-bin/rosat/rosat-survey

I think I can see Superman flying low at lower right, cape ablaze.

Unless that is the Vela pulsar.

Ann

[neufer]

I wonder what Superman's x-ray vision of the universe would be like?

http://www.xray.mpe.mpg.de/cgi-bin/rosat/rosat-survey

I think I can see Superman flying low at lower right, cape ablaze. Unless that is the Vela pulsar.

[b][color=#0000FF]A klecksograph by Justinus Kerner, published 1879[/color][/b]

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• It's a ROSAT test:

<<Klecksography is the Art of making images from inkblots. Justinus Kerner (18 September 1786 – 21 February 1862) invented this technique when he started accidentally dropping blots of ink onto paper due to failing eyesight. Instead of throwing them away, he found that intriguing shapes appeared if he unfolded the papers. He elaborated these shapes into intricate cartoons and used them to illustrate his poems. Kerner began a collection of klecksographs and poetry in 1857 titled Klesksographien Since the 1890s, psychologists have used it as a tool for studying the subconscious, most famously Hermann Rorschach in his Rorschach inkblot test. [Klecksograph] inkblots tend to resemble images because of apophenia, the human tendency to see patterns in nature.>>

[sallyseaver]

I am sad that I missed out on the fascinating discussion of magnetism and dust back in September. I was refreshing my page to see if there were responses when the discussion had moved on to a second page... now, I know better.

Thank you very much Ann, Art and Chris for more discussion and good information.
Chris, I find it very satisfying to receive this concise telling of the relevant relationships:

accretion is only spherical if the material doesn't interact like a fluid, or if the angular momentum is very low.

Ann and Art, I appreciate more dialog about the role of magnetic fields and dust. And Art, thanks so much for the great image and academic reference.

[b][color=#0000FF]Optical image of the spiral galaxy M 51 obtained with the Hubble Space Telescope, overlaid by contours of the total radio intensity and polarization vectors at 6cm wavelength, combined from radio observations with the Effelsberg and VLA radio telescopes. The magnetic field follows well the optical spiral structure, but the regions between the spiral arms also contain strong and ordered fields. Copyright: MPIfR Bonn[/color][/b]

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IF there is a dust prominence in the absence of interacting with a different galaxy, then it could mean that the dust is primarily iron (an abundant element) with it's own magnetic properties so that it does not interact in the same way as the other orbital material?

Iron is a trace component in interstellar dust. However, dust need not be composed of ferromagnetic material to be influenced by magnetic fields.

But is dust dynamically influenced by magnetic fields
(other than simply having its dipole reoriented)

Galactic magnetic fields by Dr. Rainer Beck,
Max-Planck-Institut für Radioastronomie, Bonn, Germany

<<Galactic magnetic fields can be observed in the optical range via starlight which is polarized by interstellar dust grains in the foreground. These grains are elongated and can be aligned by magnetic fields, where the major axis becomes perpendicular to the field lines. Measurements of many stars revealed a general picture of the magnetic field in the Milky Way near the Sun. Aligned dust grains also emit polarized infrared emission, which is very useful to show magnetic fields in dust clouds in the Milky Way. In prominent spiral arms the field strength can be up to 25 μG, in regions where also cold gas and dust are concentrated.>>

I am very happy with the good information presented to-date, but I would like to further explore this. Please see what you think about the following

Take a small cube of particles in a spiral galaxy, dv. In dv, we posit a high concentration of dust that has ferromagnetic properties. Now, take another small cube of particles from the same spiral galaxy, dv-nf, such that it does not contain ferromagnetic properties. For both dv and dv-nf, a classical mechanics force diagram would show the gravity vector pointing toward the center of the galaxy and the momentum vector pointing perpendicular to the gravity vector in the tangent of the directon of motion. (like where the green "v" arrow meets the "r" radius in the following picture... I'm borrowing an image rather than making my own)


For dv, there is another force component due to magnetism and this force component could affect the movement of dv so that it can rise above or below the disc of the rotating dv-nf elements.

I think that Spiral Galaxy M96 [APOD 2015 Sep 21] shows this and so does Centaurus A NGC 5128 [APOD 2015 Nov 19]
http://apod.nasa.gov/apod/image/1511/Ce ... ESO-LL.jpg

[Chris Peterson]

For dv, there is another force component due to magnetism and this force component could affect the movement of dv so that it can rise above or below the disc of the rotating dv-nf elements.

I think that Spiral Galaxy M96 [APOD 2015 Sep 21] shows this and so does Centaurus A NGC 5128 [APOD 2015 Nov 19]
http://apod.nasa.gov/apod/image/1511/Ce ... ESO-LL.jpg

I am not aware of any example of bulk dust movement in galaxies due to large-scale magnetic fields. Dust moves due to gravitational fields and due to collisions with photons and with charged particles.

[sallyseaver]

For dv, there is another force component due to magnetism and this force component could affect the movement of dv so that it can rise above or below the disc of the rotating dv-nf elements.

I think that Spiral Galaxy M96 [APOD 2015 Sep 21] shows this and so does Centaurus A NGC 5128 [APOD 2015 Nov 19]
http://apod.nasa.gov/apod/image/1511/Ce ... ESO-LL.jpg

I am not aware of any example of bulk dust movement in galaxies due to large-scale magnetic fields. Dust moves due to gravitational fields and due to collisions with photons and with charged particles.

Don't you think that classical physics is applicable to ferromagnetic material in a system with magnetic fields? Or is your response due to not reading any peer-reviewed papers on this phenomenon?

Regarding the presence of iron in dust grains, a study of 33 planetary nebulae (granted these are not spiral galaxies), this article from the Astrophysical Journal http://iopscience.iop.org/article/10.10 ... 0-40-2-108 claims that more than 90% of [a planetary nebula's] iron atoms are condensed onto dust grains. Iron is ferromagnetic, as you know. It makes sense that iron atoms would not remain in gas form but rather gravitate towards the clumps of atoms in dust grains. And it makes sense to me that iron would present optically as dark and opaque.

Near as I can tell, when astrophysicists see wisps of brown dust above or below the main disk of the galaxy, then they assume that there has been a collision of galaxies. But I assumed that this was just because they were not in familiar with the idea that brown dust could be ferromagnetic and thus subject to magnetic forces present in any galaxy.

Do you contest the idea that galaxies have magnetic fields? Near the black hole at the center of a spiral galaxy, ions and atoms are traveling rapidly in a circular path. Most atoms (other than those of inert gases) have a slight imbalance of charge. When you get ions and atoms traveling rapidly in a circular path, they create a magnetic field (known physics). ...anyway, Art has provided solid scholar-approved evidence regarding the presence of a magnetic fieldin a spiral galaxy.

[neufer]

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I am not aware of any example of bulk dust movement in galaxies due to large-scale magnetic fields.

Don't you think that classical physics is applicable to ferromagnetic material in a system with magnetic fields?

Like iron filings, ferromagnetic material will certainly line up with magnetic fields but they will only be attracted by gradients in those magnetic fields. Large-scale galactic magnetic fields really have no gradients to speak of.

[Chris Peterson]

I am not aware of any example of bulk dust movement in galaxies due to large-scale magnetic fields. Dust moves due to gravitational fields and due to collisions with photons and with charged particles.

Don't you think that classical physics is applicable to ferromagnetic material in a system with magnetic fields?

It's perfectly applicable. Which doesn't change my observation.

Do you contest the idea that galaxies have magnetic fields?

Not at all. Only that the fields are strong enough to have a significant impact on the position of dust (as opposed to the orientation of small particles), especially given the much greater effect of other forces.

[sallyseaver]

I hope it does not tax your patience too much, but I'd like to try to explain more about what I think could happen with dust lanes that are heavily populated with ferromagnetic material.

So we are looking at the M96 galaxy in the APOD associated with this thread [September 21, 2015], and I put forward Centaurus A [APOD Nov 19, 2015] as another with dust lanes that are above or below the main disk of galaxy material.

What temperature do you think the outlying dust lanes are?

Below 1043 K, the Curie temperature, ALL the magnetic domains (or magnetic moments) in ferromagnetic material align in the same direction. I figure these dust lanes are well below 1043 K.

The magnetic field generated by the circular paths of charged particles around the center of the galaxy make a magnetic field like what is generated by a current ring [shown here]. The green arrows show the direction of the north-south pole alignment of the galaxy's magnetic field. Then in the presence of this strong galactic magnetic field, the poles associated with the tiny domains in the ferromagnetic material align in the opposite direction (black arrows). [Otherwise, the alignment of like poles cause a repulsive force and the system would not be in a steady state.]

The charged particles that are circling the center of the galaxy are actually in a spiral. Sort of like groves on an LP record, there are paths close to each other at different radii from the center. Thus, the galaxy's magnetic field is not as stable as the one pictured that is due to current in a wire circle of a fixed radius. The galaxy's magnetic field can have turbulence that is felt by the outer dust lanes as a wobbling of the magnetic field. Or perhaps some of the outer rings of charged particles (galactic current rings) actually twist with respect to the inner rings. And in this case, the main disc of non-magnetic material stays put according to its initial angular momentum, but the ferromagnetic material gets a small push below or above depending on the wobble of the magnetic field experienced by the dust.

The European Space Agnecy's Planck Satellite has made observations regarding the galactic magnetic fields for the Milky Way, and it does show turbulence. See APOD for Jan 27, 2015 and the article it references: "Twisted, Tangled and Turbulent: Magnetic Fields in the Milky Way" http://phenomena.nationalgeographic.com ... milky-way/


Here is an image of the Milky Way from the Spitzer space telescope. It's infrared, but there are opaque regions that I think are optical representations of dust. [APOD March 08,2015]



Or here is another that shows dust outside of the center disk, I believe. [APOD July 24, 2014]

[neufer]

Below 1043 K, the Curie temperature, ALL the magnetic domains (or magnetic moments) in ferromagnetic material align in the same direction. I figure these dust lanes are well below 1043 K.

The thermal equilibrium temperature of dust 1 AU from our Sun
should approximately the same as that of the Earth ~ 250 K.

The brightest stars are ~10,000 as luminous as the Sun
requiring a 1 AU dust temperature 10 times higher ~ 2500 K.

The Stefan–Boltzmann law states that the total energy radiated per unit surface area
of a black body across all wavelengths per unit time is directly proportional to
the fourth power of the black body's thermodynamic temperature T:

Therefore, dust further than ~ 6 AU from any star should be colder than 1020 K (~2500/√6)

Dust further than ~ 1 light year from any star should be colder than 10 K.

[Chris Peterson]

I hope it does not tax your patience too much, but I'd like to try to explain more about what I think could happen with dust lanes that are heavily populated with ferromagnetic material.

But dust lanes are not heavily populated with ferromagnetic material. Indeed, they are not heavily populated with dust. Dust lanes are actually gas lanes, slightly contaminated with dust- all of which is overwhelmingly dominated by self-gravitation from hydrogen. And there is no strong magnetic field, nor a significant field gradient to generate motion. At the least, if galactic magnetic fields were resulting in the motion of iron and nickel, we'd see material gradients... which we don't.

So again, I'm unaware of any examples of bulk movement of dust in galaxies caused by magnetic fields. We only see the impact of magnetic fields in two places- locally (as around stars and small star forming regions), and over large distances in polarization effects and the like caused by particle orientation in weak fields.

You may have ideas about how you think some material should behave in galactic magnetic fields, but observation demonstrates that it doesn't, and solid theory explains why that is.