Behind the scenes of protostellar disk formation

Behind the scenes of protostellar disk formation
This image shows the protoplanetary disc surrounding the young star HL Tauri, revealing substructures within the disc that have never been seen before. It even shows the possible positions of planets forming in the dark patches within the system. Credit: ALMA (ESO/NAOJ/NRAO)

For a long time the formation of protostellar disks – a prerequisite to the formation of planetary system around stars – has defied theoretical astrophysicists: In a dense, collapsing cloud of gas and dust, the magnetic field would be dragged to the centre as well resulting in a braking effect. Hardly any rotationally supported disk can form this way, unless the tiny grains are removed from the cloud by growing or coagulating into bigger grains. This is the result from a new study published by researchers at the Max Planck Institute for Extraterrestrial Physics and other intuitions. The more realistic simulations now take into account non-ideal magneto-hydrodynamics and ionization chemistry to form a rotationally supported protostellar disk.

Although rotationally supported disks are frequently observed around young stellar objects, theoretical studies have found it difficult to form such disks. The main problem is the in the interstellar matter, which will lead to the so-called "magnetic braking catastrophe", even for moderate magnetic field strengths. In models using ideal magneto-hydrodynamics (MHD) the gas is "frozen" into the magnetic field, and the field lines are dragged towards the centre by the collapsing gas resulting an hourglass-shaped magnetic field. Strongly pinched field lines connect materials in the stellar vicinity and that in the envelope much further out, transferring angular momentum away from the centre. Even in non-ideal MHD models where neutral matter is allowed to drift relative to the magnetic field, the formation of rotationally supported disks remains difficult, if a standard ionization chemistry is used in computing the non-ideal MHD effects.

"The problem are the tiny ; if they are absent we do get a rotationally supported disk", states Bo Zhao, lead author of the paper now published in MNRAS. "These tiny , easily charged by absorbing ions and electrons, are effective both in coupling to the magnetic field and in collision with their surrounding molecules. In other words, the neutral matter is still relatively well coupled to the magnetic field because of these tiny grains. However, if we remove them, the larger grains do not couple as effectively and the neutral matter of the cloud can sneak much faster through the magnetic field lines and eventually form a disk with enough rotation support."

Behind the scenes of protostellar disk formation
This image shows a colour composite of visible and near-infrared observations of the dark cloud Barnard 68. At these wavelengths, the small cloud is completely opaque because of the obscuring effect of dust particles in its interior. Credit: ESO

Interstellar molecular clouds are made up of both gas and dust grains, with a "standard" distribution of grain sizes that includes a large population of nanometre-size grains. However, such a size distribution may not represent the denser part of the molecular clouds. In cold dense molecular clouds, tiny grains of nanometre size may behave as large molecules and freeze on the surface of larger dust grains. Further support for this idea also comes from centimetre-wavelength observations trying to detect emission from spinning dust grains; they too show a lack of tiny grains with size below a few nanometres in dense molecular clouds.

"When grains are mostly larger than 0.1 micrometres, the rotationally supported disks can become massive enough to be self-gravitating and evolve into rings", says Zhao. "Such a structure in 3D could easily fragment into multiple stellar systems, which may also help explain the high multiplicity of stars in our Milky Way."

"It is surprising to find that the removal of small dust grains can avoid the 'magnetic braking catastrophe' in disk formation," says Paola Caselli, co-author of the paper. "This is a breakthrough in our understanding of how protoplanetary disks form. At the same time, it demonstrates that chemistry and microphysics are crucial to the fundamental processes in the field of star and planet formation."

  • Behind the scenes of protostellar disk formation
    The collapse of a rotating molecular cloud leads to the formation of a large rotationally supported disk if very small grains are removed (b). The strong magnetic braking in the presence of very small grains suppresses the formation of such a disk (a). Credit: © MPE
  • Behind the scenes of protostellar disk formation
    The plot on the left shows the density distribution in a collapsing gas cloud for the standard distribution of grain sizes. Even though there is a concentration towards the centre, the disk is not rotationally supported, i.e. not stable enough to form stars and planets. The plot on the right shows the same, but with the smallest grains removed. In this case, there angular momentum influx to the disk leading to a much larger, rotationally supported disk. Credit: © MPE

Explore further

How do planets form?

More information: Bo Zhao, Paola Caselli, Zhi-Yun Li, Ruben Krasnopolsky, Hsien Shang, Fumitaka Nakamura, Protostellar Disk Formation Enabled by Removal of Small Dust Grains, accepted for publication MNRAS, arxiv.org/abs/1602.02729
Provided by Max Planck Society
Citation: Behind the scenes of protostellar disk formation (2016, July 11) retrieved 15 September 2019 from https://phys.org/news/2016-07-scenes-protostellar-disk-formation.html
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Jul 11, 2016
This comment has been removed by a moderator.

Jul 11, 2016
@Chris: No, they are practicing scientists, their models take into account lab plasma and can also reproduce them, or they wouldn't be used. But these are complex systems, and the problem appears for the MHD dust models that can reproduce the disks.

By the way, aren't you confusing the problem with the solution? It is the disk models that have the whole dust size range that show the problematic hourglass field, while the disk models with particle agglomeration behaves like observed disks.

Jul 11, 2016
Re: "In models using ideal magneto-hydrodynamics (MHD) the gas is "frozen" into the magnetic field, and the field lines are dragged towards the centre by the collapsing gas resulting an hourglass-shaped magnetic field." Chris_Reeve/HannesAlfven

Selective reading on your part.
The more realistic simulations now take into account non-ideal magneto-hydrodynamics and ionization chemistry...

Jul 11, 2016
This comment has been removed by a moderator.

Jul 11, 2016
Is unrealistic: the collapse of gas creates a proper disk and the star in the middle.
Realistically: Fast rotation the stars brings together disk.
Is unrealistic story always some new stories. Most of the visitors are only interested the story.
Realistically is final and shall be applied always, in the same way to the new cases. Nobody gives a shit for the truth, there is no money.
Money = science. True = only true.

Jul 11, 2016
Torborn:
This Torborn guys seems quite knowledgeable on the surface but too bad he is actually a creationist fanatic

Jul 11, 2016
This comment has been removed by a moderator.

Jul 11, 2016
I have no idea, maybe you can help me. It seems that it is the exact same logic that made the old chap call me one the other day:
http://phys.org/n...ria.html
Either way, Brexit is glorious.

Jul 11, 2016
But geez, its got to be frustrating for him, he clearly puts his time in keeping abreast of, sharing, and supporting moderately challenging cutting edge scientific ideas in a realm he is comfortable with, and then some bozo just comes along and publicly slanders him as a creationist junkie multiple times. Maybe the editors will let him write a post or two.

Jul 12, 2016
Torborn:
This Torborn guys seems quite knowledgeable on the surface but too bad he is actually a creationist fanatic
- johnhew
Terribly astute observation regarding the old Swede. What is it about Scandi atheists (and others) who seem unable to avoid sliding into threads about religious topics for the purpose of placing on review their bilious disaffection for anything that smacks of religiosity. It would be more fitting to refer to him as a smorgasbord of anti-creationist puke.

lol

Jul 12, 2016
"In cold dense molecular clouds, tiny grains of nanometre size may behave as large molecules and freeze on the surface of larger dust grains. Further support for this idea also comes from..."

...tiny grains of nanometre size MAY behave as large molecules...

Yet another example of "theoretical" and possibly heretical ideas based on "could be", "may be", "should be", "might be"...requiring "further support for the idea".

Well, at least the pictures are entertaining to look at.

Jul 12, 2016
This comment has been removed by a moderator.

Jul 12, 2016
It's only a hypothesis when based upon scientific principles, these guys are parroting magnetic reconnection and frozen-in fields pseudoscientific mumbo jumbo.

Jul 12, 2016
It's only a hypothesis when based upon scientific principles, these guys are parroting magnetic reconnection and frozen-in fields pseudoscientific mumbo jumbo.


Say what's an antigoracle monkey sock doing on the astronomy section..? aaah he still can't drive, drove off course i assume, desperate for a low rating it seems :D

Jul 12, 2016
No, they are practicing scientists,

LOL, they are practicing pseudoscientists with their "frozen" fields and moving field lines..


You spam-faced windbag. *I* am one of those scientists! Now you have made it personal.

When you study plasma at university, the gyrokinetics of ions and the associated drift and wave equations is the absolute first thing you have to master. My PhD work led up to understanding reactive sputtering for the first time. Google it if you must.

What have *you' done with your life!? All you do is to puke all over other individual's hard work, without bothering to understand any of it. The absence of respect that you show is the one you deserve yourself.

You utter ass hat wanker, when you creep back under your bridge, know that you have utterly destroyed any little basis for having other people respect you.

Jul 12, 2016
@wduckss: "Is unrealistic: the collapse of gas creates a proper disk and the star in the middle."

The article show that your claim is erroneous. Why did you bother make it?

@johnhew: "Torborn:
This Torborn guys seems quite knowledgeable on the surface but too bad he is actually a creationist fanatic"

Sorry, I don't understand. Are your commenting to me or about me?

It seems weird in any case.

The windbag - as I now have to refer him as - has not shown knowledge in anything.

And I am obviously no creationist since I am interested in astrobiology. I am no MHD specialist either, but I do know my plasmas and especially their ionization chemistry, so this is an especially interesting topic for me.

This thread is too weird, and the turd faced minion who tries to herd it is no one I can respect. I am not sure why anyone would bother to comment after his pratfall, Hurling epithets may be necessary when you are disrespected for your hard work, but that is all. I am out.

Jul 12, 2016
You spam-faced windbag. *I* am one of those scientists! Now you have made it personal.

No, as you are still parroting nonscientific clap trap regarding moving field lines and magnetic reconnection then you are *1* of the pseudoscientists. Get it right.

Jul 12, 2016
@SEU: "atheists (and others) who seem unable to avoid sliding into threads about religious topics".

Don't be ridiculous. Superstition and the attendant erroneous claims have absolutely no place in science, and this is a science site.

As doing experiments, I respond to religion like other superstitions of its kind such as astrology, homeopathy, "electric universe" and alien abductions, no difference - I am an a-theist, an a-creationist, an a-astrologist, an a-homeopath, an a-EU, an a-AA, et cetera. Based on observed facts and their rejection of all these old and new superstitions, I can be nothing else.

If you don't like people laughing at religion, do not mention it and its absurd magical details among grownups and especially among sciences. No one bothers to protest astrology if it isn't pushed into their face for no apparent reason or - worse - for the wrong reasons such as claiming it is relevant for understanding nature. It is that simple.

Jul 12, 2016
You spam-faced windbag. *I* am one of those scientists! Now you have made it personal.

No, as you are still parroting nonscientific clap trap regarding moving field lines and magnetic reconnection then you are *1* of the pseudoscientists. Get it right.


This is the one thing what is correct in your comment: You spam-faced windbag. You didn't dare to google my work and try to comment on it.

But we know this. I am out, as I noted.

Jul 12, 2016
You didn't dare to google my work and try to comment on it.

I get plenty of pseudoscience here, I don't need to go searching for it too.

Jul 12, 2016
This comment has been removed by a moderator.

Jul 12, 2016
The mark of the true crank is that they're absolutely sure they've got it all figured out for certain, and they attack real scientists because they use words like "may" and "might" when they talk about hypotheses.

The scientist is humble enough to admit they might be wrong. The crank is not.

Jul 13, 2016
they are practicing pseudoscientists
@cd
well this link proves you wrong using predominantly plasma physicists: http://www.pppl.g...%20lines

but then again, you keep stating magnetic reconnection doesn't exist too... but 100,000 experimental tests proving you wrong and stupid all in one link

http://www.pppl.g...wn-earth

the problem with eu:
1- (most important) it doesn't comply with the scientific method
2- no predictability
3- no reproducible evidence
4- misrepresented or misunderstood evidence from others
5- they think it's 1970 and Alfven is infallible

.

.

call me one
@johnhew
1- he explained in his last post on your link
2- you've historically defended irrational creationist literature and jvk's creationist comments on various threads
3- why support it when, by definition & demonstration, it isn't science?

Jul 13, 2016
@torbjorn_b_g_larsson

The real world (universe). The rotation of the body (not just the stars) creates rings. Rings have the and some of asteroids. Faster rotation and greater mass creates greater value (fast rotating stars, galaxies ..).

Article has no right (Why there is a ring, an asteroid belt or a drive around the celestial objects? Http://www.svemir...-there).

Jul 13, 2016
@SEU: "atheists (and others) who seem unable to avoid sliding into threads about religious topics".

Don't be ridiculous. Superstition and the attendant erroneous claims have absolutely no place in science, and this is a science site. .


You may not recall doing so, or prefer to pretend it never happened, but YOU have been seen in threads in which religion was referred to and its beliefs according to history, and the attempts to locate evidences for biblical history through Archaeological digs that are within the context of the article(s)...and yet you felt the need to put on display your atheism and your views on what you regard as "superstitions". After reading your anti-religious and atheistic views in such threads regarding the compatibility between religion and science, I (and others) came to determine that you see yourself as a "rabble-rouser" for the cause of an anti-God society, and that you will continue to enter into such threads having to do with religion/science.

Jul 13, 2016
The mark of the true crank is that they're absolutely sure they've got it all figured out for certain, and they attack real scientists because they use words like "may" and "might" when they talk about hypotheses.

The scientist is humble enough to admit they might be wrong. The crank is not.
- DaS

Humility is not a virtue found among Theoretical Physicists...not even the ones that I know offline. Theory is the expression of an Unknown and because it is an unknown, it is inherently full of expressions of "maybe", "could be", etc.

As CD put it:

It's only a hypothesis when based upon scientific principles, these guys are parroting magnetic reconnection and frozen-in fields pseudoscientific mumbo jumbo.


This is true. They ARE parroting hypothetical mumbo jumbo while Physorg explains their work in such a way that makes it seem like a "done deal" rather than mere hypotheses based on previous work. They then build more hypos based on the previous ones.

Jul 13, 2016
Humility is not a virtue found among Theoretical Physicists
You mean except for
Yet another example of "theoretical" and possibly heretical ideas based on "could be", "may be", "should be", "might be"...requiring "further support for the idea".


Dumb da dumb dumb. Dumb da dumb dumb duhhhhh.

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