The galactic mosh pit

Oct 22, 2013
Velocity map of the extended solar neighbourhood as seen by RAVE. Shown is a slice cut perpendicular to the plan of the Milky Way through the position of the Sun. Arrows indicate the streaming motions of the stars, the colour indicates the velocity perpendicular to the plane of the Milky Way. Credit: AIP

Astronomers have discovered that our Galaxy wobbles. An international team of astronomers around Mary Williams from the Leibniz Institute for Astrophysics Potsdam (AIP) detected and examined this phenomenon with the RAdial Velocity Experiment (RAVE), a survey of almost half a million stars around the Sun. In addition to the regular Galactic rotation the scientists found the Milky Way moving perpendicular to the Galactic plane.

It is common knowledge that our Galaxy is permanently in motion. Being a barred it rotates around the Galactic centre. It has now been discovered that our Galaxy, the Milky Way, also makes small wobbling or squishing movements. It acts like a Galactic mosh pit or a huge flag fluttering in the wind, north to south, from the Galactic plane with forces coming from multiple directions, creating a chaotic wave pattern. The source of the forces is still not understood however: possible causes include spiral arms stirring things up or ripples caused by the passage of a smaller galaxy through our own.

In this study, RAVE stars were used to examine the kinematics (velocities) of stars in a large, 3D region around the Sun - the region surveys 6500 light years above and below the Sun's position as well as inwards and outwards from the Galactic centre, reaching a quarter of the way to the centre. Using a special class of stars, red clump stars, which all have about the same brightness, mean distances to the stars could be determined. This was important as then the velocities measured with RAVE, combined with other survey data, could be used to determine the full 3D velocities (up-down, in-out and rotational). The RAVE red clump giants gave an unprecedented number of stars with which it is possible to study 3D velocities in a large region around the Sun.

The 3D movement patterns obtained showed highly complex structures. The aim was then to untangle these structures, concentrating on differences between the north and south of the Galactic plane. From these velocities it was seen that our Galaxy has a lot more going on than previously thought. The velocities going upwards and downwards show that there is a wave-like behaviour, with sloshing in and out. The novel element in our approach was true 3D observation, showing how complex the velocity landscape of the Galaxy really is. Modellers now have the challenge of understanding this behaviour, be it from ripples from an eaten galaxy or the wake from . These new findings will make it possible to make 3D models of our Galaxy much more precise.

The publication "The wobbly Galaxy: kinematics north and south with RAVE red clump giants" can be found online at arxiv.org/abs/1302.2468 and was published this month in Monthly Notices of the Royal Astronomical Society (MNRAS).

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GuruShabu
1.6 / 5 (13) Oct 23, 2013
Fascinating!
no fate
1.9 / 5 (9) Oct 23, 2013
"The source of the forces is still not understood however:"

From the paper: "The behaviour of VZ shows a surprising complexity suggestive of a wave of compression and rarefaction"

"The complexity of the vertical velocity distribution suggested by
our results would tend to point towards transient features:
they suggest a non-equilibrium state. A multi-mode travelling
wave"

From the opening paragraph: "Rather, the emerging picture is of a Galaxy
in flux, evolving under the forces of internal and external
interactions."

Those who think this stuff is easy, read the whole paper and see how much of it you get. And this math is communicative, not theoretical.

I biasly chose those three quotes based on evidence of magnetic field interaction (sue me), but the paper is very thorough and there is alot of other interactions taken into account. Duration of observation wil only make this picture become clearer.

Great work.

GSwift7
3.4 / 5 (10) Oct 23, 2013
It is amazing that they can attempt this on human time scales. It's like taking a photograph of a bunch of moving objects and figuring out which way and how fast they are all moving. I understand that they get radial velocity towards or away from us from doppler effect, but I wonder how they are getting the latteral component. I'm surprised the error bounds are manageable, even with such a large sample size. It's no wonder that this is the first time anybody has tried to do this. This is really ambitous work.
GSwift7
1.8 / 5 (11) Oct 23, 2013
I biasly chose those three quotes based on evidence of magnetic field interaction


The data should clearly show if the wave is EM or gravity, since the field attenuation would be the cube of distance versus the square of distance. If they had found giant EM waves in the galaxy, it would be a big deal, and you would have heard about it already. Since we haven't heard that news, you can rest assured that the galaxy is still operating on gravity on large scales, and not electricity. Don't get the electric conspiracy machine started on this thead, please. The EU theory is nearly the dumbest alternate theory out there. There are countless examples of observational evidence that prove it false.
no fate
1.5 / 5 (8) Oct 23, 2013
GSwift: A wave component indicates a transmission of energy is taking place between systems, they repeatedly refer to it in the paper, nothing EU about this as it is strictly describing stellar motion. Gravity waves haven't been observed yet. This could be a large external influence as mentioned in the paper... but the stars moving as though subject to a multimode travelling wave implies reaction to multiple forces, not a singular giant wavefront or gravitic purturbation.

"you can rest assured that the galaxy is still operating on gravity on large scales"

Gravity is one of the 4 wheels...the galaxy isn't a unicycle. Discerning gravitational effects from magnetic ones isn't easy when your talking about effects between star systems as the forces at the system boundaries are so weak. But it is doable, and IMO is part of this equation. If it was easy the folks who wrote the paper wouldn't have said that the source of the forces wasn't understood.
no fate
1 / 5 (6) Oct 23, 2013
Also, WRT stellar magnetic fields, there are way more than one field to figure into calculations, the inverse square rule applies to the field of a bar magnet. I think this website alone has published enough articles to demonstrate how flawed this approach is.
GuruShabu
1 / 5 (12) Oct 23, 2013
We have to take into account the EM force.
It is 10 to 36 stronger than gravity!
But as a historic heritage, presently ALL cosmological models are exclusively gravitational based.
However and fortunately, plasma cosmology is taking off.
We will see in the years to come how much we are missing because of lack of the electromagnetic force role when analysing and considering all cosmological phenomenons.
When you observe plasma behaviour you can see those "waves" all the time.
GSwift7
1 / 5 (1) Oct 24, 2013
It is 10 to 36 stronger than gravity!


Only at molecular distances. The reason gravity dominates on cosmic distance scales is because EM fields decrease in strength much faster than gravity fields. Stars do not interact electromagnetically unless they are a binary system, and even then, it's still a very weak interaction unless they are nearly touching.

No_Fate:

Oh boy, I don't know where to start.

They aren't talking about gravity waves. This is a kinetic wave moving through objects that are gravitationally bound together. Gravity holds clumps of objects in a galaxy together, such as the spiral arms. If something like a smaller galaxy passes through, it will pull part of the milky way along with it. The parts that don't get stripped away completely will bounce back and continue to oscilate back and forth along the axis they were initially pulled. They will in turn exert a pull on other nearby objects, resulting in waves of objects pulling eachother back and forth.
Mimath224
1.4 / 5 (10) Nov 28, 2013
I haven't read the arxiv article yet (will later) but intuitively wouldn't someone have noticed a smaller galaxy moving through our own? And isn't there a 3rd alternative; something like a C(?)B causing a galactic vibration?
yyz
not rated yet Nov 28, 2013
"I haven't read the arxiv article yet (will later) but intuitively wouldn't someone have noticed a smaller galaxy moving through our own?"

There are at least two known dwarf galaxies passing through the disk of the Milky Way galaxy:

http://en.wikiped...l_Galaxy

http://en.wikiped...f_Galaxy

Additionally the presence of several stellar streams in the galaxy's halo likely represent the remains of dwarf galaxies shredded in the past by the Milky Way:

http://en.wikiped..._streams
Mimath224
1.4 / 5 (10) Nov 28, 2013
yyz, many thanks. I had forgotten about the first in Sag. but didn't know about the other 2 links. Must admit though I was thinking of a much larger disturb. Obviously the researchers in the article don't think these could cause the 'wobble'.
Zephir_fan
Nov 28, 2013
This comment has been removed by a moderator.
GuruShabu
1 / 5 (10) Nov 28, 2013
to GSwift7,

You are confusing EM with the Strong Nuclear force that acts as very short distance (actually only within the atom).
The electromagnetic force has the same formulation of the gravity is was expressed by Coulomb. It has the very same expression of gravity but mass is replaced by q (charge) and it is infinite in range.
That's the force that coalesce all electrical particles (plasma) into huge "clouds" that eventually will collapse gravitationally.
Zephir_fan
Nov 28, 2013
This comment has been removed by a moderator.
Mimath224
1.7 / 5 (11) Nov 29, 2013
Zephir_fan, thanks for your concern. A lot of people here appear much more knowledgeable than me. I am here for interests sake.

to GSwift7,
You are confusing EM with the Strong Nuclear force that acts as very short distance (actually only within the atom).
The electromagnetic force has the same formulation of the gravity is was expressed by Coulomb. It has the very same expression of gravity but mass is replaced by q (charge) and it is infinite in range.


Zephir_fan, I agree with you!
GuruShabu is saying what?
The expression GuruShabu refers to, (high school stuff) the inverse square law, is basically geometrical, that is, where a uniform field intensity depends on a radius, which could include various phenomena. But, and GuruShabu should know, the grav field 'attracts only' and this makes the difference. Under GR being geometrical in character (rather than a force) it seems to me that any massive object passing through the MW would disturb..cont
Mimath224
1.4 / 5 (10) Nov 29, 2013
cont.. the MW 'geometry'. On these macro scales gravity reigns and I would agree with GSwift7 and thus have to retract my earlier post:
I ... but intuitively wouldn't someone have noticed a smaller galaxy moving through our own? And isn't there a 3rd alternative; something like a C(?)B causing a galactic vibration?

Ha, my lack of expertise showing eh?
I think this article shows just how hard researchers work and this ones a gem.
regards to all