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Previous Next Up Topic Cosmology / Alternative Cosmology / Stellar Jets (4487 hits)
By Mike Petersen Date 2009-02-11 14:06
I decided to copy the entire contents of the article I found about Stellar Jets birth.  I believe this experiment to be much more important than anyone may think.  They didn't go far enough in their extrapolation.  I think they could have said something like, "So, since none of the plasma actually made it into the hole, does that mean that none of the material in an accretion disk ever makes it into the black hole in the center?  Is it possible that black holes don't swallow anything at all, but rather simply eject it?"

It's possible that black holes may actually be white holes, as Halton Arp has said.

Opinions?

Stellar Jets Born Knotted

Some of the most beautiful structures observed in the Universe are the intricate jets of supersonic material speeding away from accreting stars, such as young proto-stars and stellar mass black holes. These jets are composed of highly collimated gas, rapidly accelerated and ejected from circumstellar accretion disks. The in-falling gas from the disks, usually feeding the black hole or hungry young star, is somehow redirected and blown into the interstellar medium (ISM).

Much work is being done to understand how accretion disk material is turned into a rapid outflow, forming an often knotted, clumpy cloud of outflowing gas. The general idea was that the stellar jet is ejected in a steady flow (like a fire hose), only for it to interact with the surrounding ISM, breaking up as it does so. However, a unique collaboration between plasma physicists, astronomers and computational scientists may have uncovered the true nature behind these knotted structures. They didn't become knotted, they were born that way…

"The predominant theory says that jets are essentially fire hoses that shoot out matter in a steady stream, and the stream breaks up as it collides with gas and dust in space—but that doesn't appear to be so after all," said Adam Frank, professor of astrophysics at the University of Rochester, and co-author of the recent publication. According to Frank, the exciting results uncovered by the international collaboration suggest that far from being a steady stream of gas being ejected from the circumstellar accretion disk, the jets are "fired out more like bullets or buckshot." It is therefore little wonder that the vast stellar jets appear twisted, knotted and highly structured.

A member of the collaboration, Professor Sergey Lebedev and his team at the Imperial College London, made an attempt to replicate the physics of a star in the laboratory, and the experiment matched the known physics of stellar jets very well. The pioneering work by Lebedev is being lauded a possibly the "best" astrophysical experiment that's ever been carried out.

Using an aluminium disk, Lebedev applied a high-powered pulse of energy to it. Within the first few billionths of a second, the aluminium began to evaporate, generating a small cloud of plasma. This plasma became an accretion disk analogue, a microscopic equivalent of the plasma being dragged into a proto-star. In the centre of the disk, the aluminium had eroded completely, creating a hole. Through this hole, a magnetic field, being applied below the disk, could penetrate through.

It would appear that the dynamics of the magnetic field interacting with the plasma accurately depicts the observed characteristics of extended stellar jets. At first, the magnetic field pushes the plasma aside around the disk's hole, but its structure evolves by creating a bubble, then twisting and warping, forming a knot in the plasma jet. Then, a very important event occurs; the initial magnetic "bubble" pinches off and is propelled away. Another magnetic bubble forms to continue the process all over again. These dynamic processes cause packets of plasma to be released in bursts and not in the steady, classical "fire hose" manner.

"We can see these beautiful jets in space, but we have no way to see what the magnetic fields look like," says Frank. "I can't go out and stick probes in a star, but here we can get some idea—and it looks like the field is a weird, tangled mess."

By shrinking this cosmic phenomenon into a laboratory experiment, the investigators have shed some light on the possible mechanism driving the structure of stellar jets. It appears that magnetic processes, not ISM interactions, shape the knotted structure of stellar jets when they born, not after they have evolved.

By Jade Annand Date 2009-02-12 07:36
I don't know... it's hard to tell from here whether they are talking about redirecting all of the in-falling gas or merely some (or most) of it. There's nothing in the article talking about means to measure such things.

I'd be intrigued to know how similar the processes really are, and what differences we would expect a black hole to show in comparison to a protostar, and whether we find any such differences. How are black holes on intrinsic magnetic fields? How much ought they interfere with a magnetic field or effect generated by the surrounding material?

Almost all of this work is being done in simulations, by necessity so far, given the spread and lack of ability to observe the jet origins (is there any observatory we're going to launch that could ever help that, or are we doomed by the nature of protostars?). In Machida et al's Driving Mechanism Of Jets..., they simulate ways to get jets from protostars that would explain outflow and jets - this requires collapsing clouds and other features of stellar formation. I wonder if the protostar jet and black hole jet folks are talking to one another at all; they should if they're not.

It's tough to tell at this point whether SMBH's, if they exist, are putting out jets from gas that they are being fed, or whether they are actually creating hydrogen on the fly, or whether the centers of galaxies aren't actually SMBH's, but rather, big-ass protostars :)
By Ari Jokimäki Date 2009-02-13 07:49
It's possible that black holes may actually be white holes, as Halton Arp has said.

Opinions?

I think observational data says that - assuming Halton Arp's views are correct - stellar jets should have different mechanism than galactic jets. That is because we don't see remarkably redshifted small stars near jetting bigger stars, but Arp's claim is that matter ejected from galaxies has substantial intrinsic redshift. If stellar jets would have same mechanism than galactic jets, we should see small stars with large intrinsic redshifts around big stars.
By Jade Annand Date 2009-02-15 16:48
Ari said:

If stellar jets would have same mechanism than galactic jets, we should see small stars with large intrinsic redshifts around big stars.


Is there enough cohesiveness in those stellar jets to even make other stars?

Then again, I'm not totally convinced of the variable mass hypothesis; I'd be leaning to the intrinsic redshifts being indicative of something else. Perhaps that's just me, though :)

The K effect is more a feature of early-type stars. Have we ever noticed O-type main sequence stars like AE Aurigae in a configuration that might indicate a stellar jet origin?
By Ari Jokimäki Date 2009-02-18 05:32
Ritchie said:

Is there enough cohesiveness in those stellar jets to even make other stars?

I have no idea about that. Perhaps we soon get some redshift measurements of those brown dwarfs / exoplanets they keep finding...
By Jade Annand Date 2009-02-21 06:06
Ari said:

Perhaps we soon get some redshift measurements of those brown dwarfs / exoplanets they keep finding...


I think the chances of an exoplanet being created from jet material would be pretty low - it's one thing to have the jet coalesce or collimate, but even that would be just a diffuse cylinder or cigar. If gravity were enough to bring the gases back in, then the furthest point away might be a little bit denser, but if that were enough to make anything form, it would seem to me that any orbit it would take up would be a very, very narrow ellipse.

Could something else capture the object? I've always wondered whether it would actually be possible for a star system to actually capture something else. It seems to me like accretion and overspin would be much, much more likely than capture. It seems any time I've simulated gravity, any object enter the system has a near-100% chance of making it out of that system again, barring collision or intricate gravity dance with already-present planets. A star on its own could do little.

Exoplanets have made astronomy interesting again, and they're helping push the envelope with observation techniques. I'm pretty intrigued to see what we will know about exoplanetary systems in the next 10 years.
By Ari Jokimäki Date 2009-02-24 12:24
Ritchie said:

I think the chances of an exoplanet being created from jet material would be pretty low - it's one thing to have the jet coalesce or collimate, but even that would be just a diffuse cylinder or cigar. If gravity were enough to bring the gases back in, then the furthest point away might be a little bit denser, but if that were enough to make anything form, it would seem to me that any orbit it would take up would be a very, very narrow ellipse.

But if we assume variable mass hypothesis correct, then the mass of the ejected matter would grow which would act like brakes, so there would be some condensing due to that. I have no idea if it would be sufficient to form any objects out of that, though.
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