The turbulent interstellar medium

The turbulent interstellar medium
The galaxy M101 as seen in the optical and in the light of atomic hydrogen gas (red). The hydrogen lines reveal that the gas is rapidly moving and turbulent, and a new study of turbulence in galaxies concludes that in many cases it is generated not by star formation but by gravitational effects alone. Terry Hancock

The gas in galaxies is typically seen to be moving at very rapid, even supersonic velocities, providing clear evidence that the medium is highly turbulent. Looking more closely at gas clouds in our own Milky Way, astronomers have similarly demonstrated using a variety of different observations that the interstellar medium is turbulent. Turbulence is a key physical parameter in the star formation process because, like the thermal pressure of warm gas, it counters the collapse of clouds into stars from gravitational contraction. Despite its importance and ubiquity, however, turbulence is poorly understood. Even its origin is far from clear. Some scientists argue that turbulence results from star formation itself, as new stars and their associated supernovae drive winds that stir up the interstellar medium. Other astronomers counter that the influence of gravity alone is enough to induce supersonic motions in gas as it moves through and across a rotating galaxy.

CfA astronomer Blakesley Burkhart and her colleague examine in theoretical detail the physical processes involved in generating turbulence, and compare their conclusions with observations of galaxies. It has long been noted that the in galaxies appears to correlate approximately with the spread of gas velocities seen in that galaxy. Indeed, that result was one of the reasons that a causal link between star formation and turbulence was proposed. The scientists point out, however, that if star formation were responsible for that spread then the correlation would be much tighter than is observed.

Actually, the gravity-driven model of turbulence shows much better agreement with the data. For example, the latter has no trouble reproducing galaxies with very high velocities yet having very low star formation rates; in these situations there is just not much gas to make , but gravity nevertheless drives the fast motions. The scientists' results are highly suggestive though not definitive, and very likely there are cases where both and gravity play comparable roles.

The authors conclude by discussing the limitations of the current observational dataset, and they suggest future measures to refine their conclusions, but in the meantime they have demonstrated that has a more complicated origin than was typically thought.


Explore further

The jet of a black hole drives multiple winds in a nearby galaxy

More information: "Is Turbulence in the Interstellar Medium Driven by Feedback or Gravity? An Observational Test," Mark R. Krumholz and Blakesley Burkhart, MNRAS 458, 1671, 2016.
Citation: The turbulent interstellar medium (2016, May 9) retrieved 15 October 2019 from https://phys.org/news/2016-05-turbulent-interstellar-medium.html
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May 09, 2016
Sadly you could certainly take courses on gas physics but of course it wouldn't do you any good whatsoever regarding the above. The dynamics of plasmas are completely different from gas dynamics, you may as well describe the crystalline aspects of water ice using gas dynamics. Obviously FSC isn't concerned with using the proper physics or even aware that plasma is not gas and specific physics MUST be used to describe plasma.

Funny thing is the "scientists" above use the same incorrect physics FSC refers to, they too suffer from ignorance of omission. As such, these findings and all others describing this plasma as gas are meaningless BS.

May 09, 2016
The interactions in the interstellar medium can drive the flow supersonic. supersonic flow, by definition, is going faster than the speed on sound. Some argue space has no sound, but 10^8 particles per cubic centimeter is enough from statistical mechanics, and galaxies form at that or higher. Speed varies, but 200-300 m/s is a decent range. Local relative velocities are often higher than that, so you get lots and lots of shockwaves. Also, large regions have bulk velocity. A stable galaxy or solar medium has velocity WAY higher than this in the absolute frame just by rotation. There are shockwaves in the solar system though. The solar wind is supersonic, and has a termination shock where it meets the neighborhood interstellar medium. There should also be a bow shock from our sun moving at supersonic speed relative

plasma physics is not that remarkably different from gas physics in many flow regimes. Many problems can be modeled using a two-phase (electrons,ions) charged flow.

May 09, 2016
plasma physics is not that remarkably different from gas physics in many flow regimes. Many problems can be modeled using a two-phase (electrons,ions) charged flow.

That's what many would like to think, but in situ measurements since man has ventured into space show basically the opposite of what you are claiming. Sure, the "problems" can be modeled erroneously, but the result is erroneous as well. Until the fallacy of gas=plasma physics is realized the mysteries, unexpectedness, general ignorance of these processes will remain.

May 09, 2016
Re: "We are talking atomic hydrogen here. Atomic hydrogen is not a plasma. Stop bringing up plasma."

An ionic wind will drag the neutrals, Sherlock.

May 10, 2016
...neat theory

It's an abomination of science to claim this is a theory, a hypothesis at the most but more definitely just a guess based upon ignorance of the matter involved.

May 10, 2016
That may be so, but we're talking here of the ISM, which is not a plasma, but rather a complex system consisting of many components, baryonic and non-baryonic matter, magnetic fields and radiation fields

You're had better send a memo to NASA, because according to them the ISM is plasma. Your "non-baryonic" component is purely hypothetical, and your magnetic/radiation fields are there due to the plasma. Although complex, it all still behaves as a plasma as it only need be partially ionized to behave as a plasma. You're really going off the deep end of ignorance by claiming this is not plasma, all "authorities" of space science agrees it is undeniably plasma.

May 10, 2016
@lengould:

I am not sure I completely understand your questions. but if you want scientific facts do stay away from the EU crackpots (cd, HA) that tries to confuse simple (well) gas physics with their pseudoscience ideas.

FSC et cetera are very helpful on the actual physics.

Your last question reminds me of the analogy of the exhaust from a rocket or supersonic jet engine, which do transmit sound waves even as they are plowing into the subsonic ambient atmosphere.

Shock waves, not only sound waves, are the usual result from that meeting.

A similar situation happens when you try to move parts of a rock faster than the sound travel through it, i.e. at a detonation or rapid impact. You get shock waves transmitted through the surrounding rock, while the detonation/impact zone fragments, heats, melts et cetera, precisely because the energy can't be dispersed as fast as it is imparted. (The typical energy dispersal happens at the speed of sound.)

May 10, 2016
What is the speed of sound in interstellar space, and how can the gas medium which would presumeably transmit sound travel faster than sound can travel through it?
@lengould:
and to piggyback on FSC and TBGL: look into actual plasma physics, not electric universe delusional beliefs
start here: http://www.pppl.gov/

here are some free courses
http://ocw.mit.ed...ll-2006/

http://ocw.mit.ed...ng-2007/

http://ocw.mit.ed...ll-2003/

more importantly, even engineers who study nothing but plasma physics will tell you that MHD has all you need to know WRT plasma physics

before accepting the word of a random electric acolyte on this site, talk to actual plasma physicists on one of my links from universities who aren't trying to sell you a religion or con (or book)

May 10, 2016
What is the speed of sound in interstellar space,
No, what is the speed of sound in gas ions in interstellar space. Remember that ions can interact across empty space without having to collide. They're charged.

and how can the gas medium which would presumeably transmit sound travel faster than sound can travel through it?
No, how can you measure how fast the gas medium is traveling. It's moving through empty space. It might as well be standing still.

After all, the Earth's atmosphere is moving East at 600 mph, on average; pretty close to the speed of sound, and well exceeding it at the Equator. Doesn't seem to stop you from hearing someone clap their hands behind you. Just sayin'.

May 11, 2016
Critical ionization velocities is one of those tidbits that isn't considered but is likely relevant. Verschuur has shown this relationship of CIV in these HI "clouds", we're almost certainly discussing plasma here and the proper physics should be used. Such as, not gas.

May 11, 2016
Stop discussing electrons, protons. We are discussing atomic hydrogen observed in the ground state by the 21 cm hyperfine interaction line.
Plasma, not.

LOL, when you're looking through the telescope do you actually see the sign that says "electrons and ions: do not enter this cloud" or "atomic hydrogen only beyond this point". Unless you have a mechanism that can prevent with absolute certainty any electrons or ions from entering the cloud you're pissing head long into the wind. You're used to that though, aren't you.

https://www.googl...mkWpTyaQ


May 11, 2016
@DS
ions can interact across empty space without having to collide. They're charged
The most common particle interactions in the ISM are electron-electron, electron-proton and electron-(H, He), and are basically elastic collisions - the charge plays virtually no rĂ´le here except right up close.
Ummm, I'm gonna point out here that elastic collisions are right up close. By definition.

Typical densities are ~1/cm^3, speeds are of the order of 100's of km/s, and mean free paths between collisions on the order of 100's of AU.
I don't see that this makes much difference in an HII region hundreds or thousands of light years across.

You might want to rethink your statement.
You might want to rethink your apparently erroneous interpretation of my statements.

No, how can you measure how fast the gas medium is traveling
Duh - doppler shifting of emission or absorption lines.
Duh, from what frame of reference?

May 11, 2016
Worth pointing out that my point was, @lengould is asking the wrong questions, because they are based on incorrect assumptions.

@FSC, you seem to have totally missed this.

May 11, 2016
I also have a reference saying that.....

Your "reference" is wiki, if you're going to claim this absolute condition I think a primary source explicitly saying that cosmic radiation at any energy (including x-ray and gamma) cannot under any circumstance penetrate these clouds.
Rudeness does not hide your lack of scientific argument, but it may work out on the street.

That's laughable, as if you haven't directed acrimony toward me at every opportunity. You only try to change the subject due to your baseless argument.

These "pockets of ionized gas with neutral cores" is exactly what one would expect due to plasma processes. This process is called Maryland Convection and the observed results matching the prediction of interstellar Birkeland currents. Needless to say this doesn't change the fact that those pockets are feeling the forces imposed by surrounding plasma rather than gravity.
http://www.ptep-o...1-13.PDF

May 12, 2016
These "pockets of ionized gas with neutral cores" is exactly what one would expect due to plasma processes. This process is called Maryland Convection...


"Maryland convection" - a phrase literally nowhere to be found on the internet besides here. Where are you pulling this stuff from?

May 12, 2016
"Maryland convection" - a phrase literally nowhere to be found on the internet besides here. Where are you pulling this stuff from?

Sorry Marklund Convection, the auto spell on the Android device is maddening to say the least.

May 12, 2016
(including x-ray and gamma) cannot under any circumstance penetrate these clouds.


I nor anyone I referenced to ever made this misguided statement.
I'd be very cautious in taking a position either way on this. OTOH, all @Phys is saying is nobody said it, so I agree with that.

May 12, 2016
@Phys, your reference is supplemented by the Wikipedia article on HI regions:

https://en.wikipe...I_region

Near an expanding H II region is a dense HI region, separated from the undisturbed HI region by a shock front and from the H II region by an ionization front.
This is referenced here: http://adsabs.har...6/146109 The full paper may be downloaded for free on that page.

May 12, 2016
I nor anyone I referenced to ever made this misguided statement.

Really? But you said...
So indeed ions and electrons, aka plasma, are in fact stopped from entering volumes of (relatively) cold neutral atomic hydrogen.

Please clarify your double speak. Are particles "indeed" stopped from entering "beyond this point" or not?

The wikipedia article...

Is not a primary source and can be edited by anyone. Obviously since not one college (or otherwise) professor who is worth his salt would ever accept wiki as a source you obviously do not respect the entirety of academia.
If you portray Higgs as a clown, then you yourself are the fool.

This is probably true.
If you disrespect science

I don't put science on a pedestal, it's just as fallible as any other human endeavour. I appreciate the ideal of what science should be or is claimed to be, but it is not that now or for about 100 years.
BTW, I don't yearn for your respect.

May 14, 2016
You misquoted me by adding any kind of electromagnetic radiation to "ions and electrons, aka plasma".

No, you just displayed your typical myopic POV. Let's see what hyperphysics has to say...

http://hyperphysi...mic.html

"Almost 90% of the cosmic rays which strike the Earth's atmosphere are protons (hydrogen nuclei) and about 9% are alpha particles. Electrons amount to about 1% according to Chaisson & McMillan."

So, cosmic rays are indeed ions and electrons. Hmmm....

Lest we not forget another current article on the pseudoscience magnetic reconnection and the direct measurements taken by the MMS. The "shock fronts" and ionization fronts DA alluded to are plasma sheaths, and as we have known since Langmuir these surface features exchange energy via electric currents, beams, and e-fields. Processes which in situ measurements have shown DO NOT prevent electrons and ions from crossing boundaries.

It's OK to admit when you are wrong.

May 14, 2016
The wiki article sketches what is going on and bases itself on the latest greatest research.

Wiki and it's users actively participate in censorship, as such it is nothing more than a propaganda outlet for the currently accepted viewpoints.
https://sites.goo...nnection

The Eiffel tower is still standing and so is the Coliseum.
Some human endeavours are performed by people who really know what they are doing.

That's engineering, and quite frankly, engineers are held in much higher regard than theoreticists by me as they actually deal in real physics rather than mathematical gymnastics and fanciful thought experiments.

May 14, 2016
This comment has been removed by a moderator.

May 14, 2016
That's engineering, and quite frankly, engineers are held in much higher regard than theoreticists by me as they actually deal in real physics rather than mathematical gymnastics and fanciful thought experiments.

You were saying "... science .. is just as fallible as any other human endeavor."
I can show you a list of human endeavors that are still standing after up to 2500 years.
So your relativism is over the top.

May 14, 2016
Actually, I have to weigh in when I see someone claim that science is as fallible as religion.

I don't see science claiming there is a super magic daddy in the sky; I don't see science claiming that stone age sheep herders were capable of figuring out where the world came from; I don't see science claiming that wearing nylons with a wool dress is evil; and I don't see science claiming that it's OK to kill babies because their parents believe a different kind of science.

I think that'll do.

May 14, 2016
I don't see science claiming there is a super magic daddy in the sky;

True, but it is pervaded by super magic fairy dust.
I don't see science claiming that wearing nylons with a wool dress is evil;

But it does claim driving a car is evil.
and I don't see science claiming that it's OK to kill babies because their parents believe a different kind of science.

That's left up to planned (baby parts factory) parenthood.

May 15, 2016
I will point out here that science found the dark matter. It's not like they tried to hide it, and it's not like they went around making up stories about it. Doing either of those things would be failing; but they don't. They just keep looking until they find out, and when they find out, then we know.

If science were religion, they'd make up a story about it.

If science were politics, they'd try to hide it.

That's the whole point. And you just don't get it, @cd. I think it's highly amusing that you're trying to make up stories about science, and then saying something like this.

May 15, 2016
@cd45
Either there is extra mass that we do not observe yet, or Newton's laws of gravity fail.
So you opt for failure of Newton's gravity.

Newton's gravity works pretty well, save a few special cases, for the scales at which it is relevant. The failure is the misapplication of his and other theories to explain phenomena well beyond this physical relevance. Your comment shows the same myopic POV you typically show while posting, there is at least one other option to your either/or claim. That is the matter involved displays/behaves to properties that are not currently accounted for correctly. When the full electrodynamic properties of the plasma which makes up 99.999% of the Universe is considered there is no need to rely on magic fairy dust to prop up failed theories.

May 15, 2016
I will point out here that science found the dark matter. It's not like they tried to hide it, and it's not like they went around making up stories about it. Doing either of those things would be failing; but they don't. They just keep looking until they find out, and when they find out, then we know.

Science didn't find DM, it was forced into corner that required DM because the currently accepted theories misrepresent the behavior/properties of the matter by about 80%. And you're right, they never tried to hide it due to the fact that it presents an unlimited financial opportunity for generations of pseudoscientists to live off of the tit of the taxpayers. And you're also right that they just keep looking, and looking, and looking.... And billions of dollars later they just keep looking.


May 15, 2016
If science were religion, they'd make up a story about it.
If science were politics, they'd try to hide it.

Obviously you aren't familiar with the debate surrounding the theory of the aurora between Chapman/Birkeland. It really wasn't much of a debate as Chapman took the religious/political side and misrepresented, obfuscated, and omitted Birkeland's findings for over 60 years. He proactively prevented discussion of Birkeland's views in favor of his own mathematically based POV's at conferences he and his cronies organized. Birkeland's findings were developed via direct observation and laboratory experiment (real honest to goodness science), but still this was ignored for decades in favor of purely theoretically developed mathematical equations(the ones still being used to describe the ISM). Only after direct, irrefutable in situ measurements was it shown Chapman was wrong, Birkeland right. I think it's highly amusing that you don't get how science works, it's still people.

May 15, 2016
This comment has been removed by a moderator.

May 15, 2016
Now you have an absolutely clear picture of how that vacuous cavern Benni/bschit calls a mind works. A few posts ago I accused that twerp of banging on constantly about beatings to the point that it must have S&M fantasies. Out of bunni's mouth, that somehow becomes MY S&M fantasies. I think it finally gives me a clue about how it "thinks". You scan the line, pick out your favorite words, and arrange them in a sentence. Doesn't matter if it has any relationship to the original content. We've met people like this. They're bone deep sophists. You know, the type that has one great-grandparent that was native American, but takes an extreme stand about "our people" whenever there's any reference made to that demographic in a stupid joke. You're a woman aren't you, and I'm betting of the "stay at home fraud" variety.


May 15, 2016
[cont]

Its sense of victimization is another give-away. Part of that American trend that your victimization status is your identity. "Oh, I'm persecuted because I don't conform to the establishment's ideas about science!!!" "They want to beat me for it!" Since you have no reading comprehension, I'll spell it out for you. The recurring dream to beat some courtesy into trolls' heads was not about their POV. It was about rudeness. Simple proposition. Spare the rod, spoil the child. You're living proof. People that are as rude as you simply have had no consequences for that behavior. You're a weed in this garden of science. You're not the wrong species, you're uninvited, unwelcome, and contribute nothing. That is usually ignored. You're rude on top of it though. I really feel for your SO (you know, the whatever creature pays the bills and puts up with your BS. The one that also accuses you of sophistry.)

May 15, 2016
"Benni: Does anyone else feel a sudden breeze?"

No. I think that's the new one you've been cut.

May 15, 2016
bschott 1.4 /5 (10) May 12, 2016

cantdrive85 1.6 /5 (13) May 09, 2016
Sadly


you're on this thread.


What was the point of this post?


The points about your reading comprehension weren't exaggerated! I'll summarize for you. GO AWAY!

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