New studies give strong boost to binary-star formation theory

Dec 31, 2013
Binary star formation through disk fragmentation starts (left) with a young star surrounded by a rotating disk of gas and dust. The disk fragments under its own gravity, with a second star forming within the disk (center), surrounded by its own disk. At right, the two stars form an orbiting pair. 100 Astronomical Units (AU) is roughly the diameter of our Solar System. Credit: Bill Saxton, NRAO/AUI/NSF

(Phys.org) —Using the new capabilities of the upgraded Karl G. Jansky Very Large Array (VLA), scientists have discovered previously-unseen binary companions to a pair of very young protostars. The discovery gives strong support for one of the competing explanations for how double-star systems form.

Astronomers know that about half of all Sun-like stars are members of double or , but have debated over how such systems are formed.

"The only way to resolve the debate is to observe very young stellar systems and catch them in the act of formation," said John Tobin, of the National Radio Astronomy Observatory (NRAO). "That's what we've done with the stars we observed, and we got valuable new clues from them," he added.

Their new clues support the idea that double-star systems form when a disk of gas and dust whirling around one young star fragments, forming another new star in orbit with the first. Young stars that still are gathering matter from their surroundings form such disks, along with jet-like outflows rapidly propelling material in narrow beams perpendicular to the disk.

When Tobin and an international team of astronomers studied gas-enshrouded young stars roughly 1,000 light-years from Earth, they found that two had previously-unseen companions in the plane where their disks would be expected, perpendicular to the direction of the outflows from the systems. One of the systems also clearly had a disk surrounding both young stars.

"This fits the theoretical model of companions forming from fragmentation in the disk," Tobin said. "This configuration would not be required by alternative explanations," he added.

The new observations add to a growing body of evidence supporting the disk-fragmentation idea. In 2006, a different VLA observing team found an orbiting pair of young stars, each of which was surrounded by a disk of material. The two disks, they found, were aligned with each other in the same plane. Last year, Tobin and his colleagues found a large circumstellar disk forming around a protostar in the initial phases of star formation. This showed that disks are present early in the star formation process, a necessity for binary pairs to form through disk fragmentation.

"Our new findings, combined with the earlier data, make disk fragmentation the strongest explanation for how close multiple star systems are formed," said Leslie Looney of NRAO and the University of Illinois.

"The increased sensitivity of the VLA, produced by a decade-long upgrade project completed in 2012, made the new discovery possible," Claire Chandler of NRAO said.

The new capability was particularly valuable at the VLA's highest frequency band, from 40-50 GHz, where dust in the disks surrounding young stars emits radio waves. The astronomers observed the during 2012 with the VLA and with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) in California.

Tobin, Chandler, and Looney were part of a research team of astronomers from the U.S., Mexico, and the Netherlands. The scientists published their findings in the Astrophysical Journal.

Explore further: Old young stars

More information: iopscience.iop.org/0004-637X/779/2/93/

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User comments : 13

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cantdrive85
1 / 5 (13) Dec 31, 2013
Blah, blah, blah, GIGO!
tadchem
5 / 5 (6) Dec 31, 2013
Gravity provides a positive feedback mechanism. Local perturbations in the density of the gas/dust cloud are amplified by gravity-driven condensation. The effect is similar to a Raleigh-Taylor Instability. The inherent angular momentum of the cloud defines the ecliptic plane, the rotation of the substructures (vortices) and aims the jets of escaping gas.
cantdrive85
1 / 5 (12) Dec 31, 2013
Blah, blah, blah, nonsense. Trying to describe this plasma with gas laws again?
Returners
1 / 5 (4) Dec 31, 2013
One glaring flaw in all of this is the pathetic assumption that there is only one way to make a binary system.

In fact, this theory can only explain binaries where both stars rotate in the same plane. It doesn't even make sense when applied to binaries where the individual stars have vastly different planes of rotation, nor trinary systems where there is more than one orbital plane involved.

Yes, I know the difference between rotate and revolve (orbit,) so if I lost you, re-read the paragraph again.

The point is that if it's possible to have threes stars where at least one of them is not on the same orbital plane as the other two, and we already know it is possible, then that means there is more than one way to form a multi-star system, since a fractured disk can't explain the third star in any case.
MandoZink
5 / 5 (6) Jan 01, 2014
One glaring flaw in all of this is the pathetic assumption that there is only one way to make a binary system.

It appears you may have assumed that since they said ...

"The discovery gives strong support for one of the competing explanations for how double-star systems form"

... and ...

"This configuration would not be required by alternative explanations"

... and ...

"Our new findings, combined with the earlier data, make disk fragmentation the strongest explanation for how close multiple star systems are formed"

... that they were claiming this was the ONLY way binary systems form.

What they merely did was establish strong support for one type of binary star formation among several configurations that may occur.
Returners
1 / 5 (5) Jan 01, 2014
"Our new findings, combined with the earlier data, make disk fragmentation the strongest explanation for how close multiple star systems are formed"

... that they were claiming this was the ONLY way binary systems form.

What they merely did was establish strong support for one type of binary star formation among several configurations that may occur.


The last quote you made, which I left in tact, is the one in question, because it is drawing a conclusion that the disk fragmentation model is "stronger" than others, thereby implying it is the "one". Ordinarily in science when people use statements like that they are essentially excluding the others.

katesisco
1 / 5 (3) Jan 01, 2014
I suspect the 'second' star is the off loaded or rejected dirty gas. Perhaps it all depends on how strong the magnetic field surrounding the star is. Strong magnetic field equals round pure star. Weak field equals star incorporating dirty gas which shortens life.
Returners
2.8 / 5 (4) Jan 01, 2014
I suspect the 'second' star is the off loaded or rejected dirty gas. Perhaps it all depends on how strong the magnetic field surrounding the star is. Strong magnetic field equals round pure star. Weak field equals star incorporating dirty gas which shortens life.


Experiments in space suggest that the initial seed objects in clouds of gas and dust begin to form and clump together due to the static electricity, i.e. the electromagnetic force, however, I don't think that's related to the "Magnetic field" in the sense of anything like ferromagnetism. Gravity is sufficient to explain the formation of stars from extended clouds of dust and gas.

If you have trouble figuring out why that is true, you can just use Newton's shell theorem. For any mass distributed across a finite distance in a shell (or a disk though that's a bit different) it will eventually collapse. It also doesn't necessarily take a long time, but does depend on the angular momenta with respect to the CoG.
Returners
3 / 5 (4) Jan 01, 2014
High angular momenta would mean the "region" in the cloud will take a long time to fall in, or may form a stable orbit and turn into a solid object as it experiences it's own gravitational collapse.

Low angular momentum would mean a given region will spiral inward more quickly, and become part of the star.

No angular momentum would mean that particular region of dust and gas would simply fall straight into the CoG along the shortest possible path, assuming that particular cloud doesn't get accelerated by colliding with another cloud which is moving along the way.

So I see no reason to invoke magnetism as a primary formative agent of Stars, as you can explain the entirety of the collapse of a hypothetical extended cloud using nothing but Newton's gravity, without invoking any other forces, provided the cloud starts out "cool enough" so that gases don't get accelerated away and escape.
Osiris1
not rated yet Jan 01, 2014
Space is a wild place, a chaos if few rules and probably a lot of collisions given the size of space and the total of stars involved. Space is not empty! Perhaps Einstein's 'c=3*(10^5)Km/sec in a vacuum' is really a 'terminal velocity' in a non empty medium, just like 'c' in glass.

It therefor is always conceivable that stellar or other objects can acquire satellites, some in long stable orbits and some not. That would probably explain many odd multi-star systems. Given orbital mechanics and the prevalence of possibilities in a seeming infinity of space occupied by bodies the size and number known only to God, many things are possible. So the onus of proof is more to show convincing impossibility rather than the opposite. Of course this does not rule out combinations of possibilities.

I believe just about all stars form from circumstellar disks. Therefore most or even all form planets as well. Stars are just planets that got......bigger!
Returners
1 / 5 (2) Jan 01, 2014
Osiris1:

Obviously scientists acknowledge that "capture" scenarios can and do happen, however, it seems much "easier" for objects to originate in the same general region of space, perhaps in the same nebula, because their relative velocities will be more comparable to one another.

The probability of an "alien" object from another star system or another star cluster matching the exact velocity to fall into a stable orbit must be lower than the probability of those objects being formed together in same area. The larger the distance between two "events" the larger the total error caused by a very minor deviation, which means that if object B is ejected from System B it has an enormous opportunity to MISS being captured by "System A", and only a very tiny probability of just so happens to be caught by "System A". Even a light year's distance could produce a situation where being off by a fraction of a degree on heading would make the difference between capture and total miss.
philw1776
not rated yet Jan 01, 2014
I see nothing here at 1st glance in this theory and observation which prohibits the formation of planetary systems close to each star or around the pair. Kepler has shown that multiple stars do have planets, sometimes even a planet that orbits around a pair of stars.
GSwift7
5 / 5 (1) Jan 03, 2014
The last quote you made, which I left in tact, is the one in question, because it is drawing a conclusion that the disk fragmentation model is "stronger" than others, thereby implying it is the "one".


The disk fragmentation theory would apply only to close binary pairs, where they do share a common ecliptic. The reason such a theory has been proposed is due to the high number of this type of binary, and how unlikely it is for so many capture events to have happened.

Our own sun is believed to have formed in a cluster, with a few other stars. Stars formed in clusters, but not as binary pairs, are probably more likely to combine into binary or trinary systems that do not have a common ecliptic. The relative percentages of the different types of binary pairs would reflect this scenario quite well.