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shunyadragon
11-08-2014, 04:44 AM
A huge radio telescope in Chile has captured the best-ever image of planets forming around a distant star, researchers say.

The spectacular view of planet birth, taken by the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile, shows numerous concentric rings in the disk of dust and gas surrounding HL Tau, a sunlike star found about 450 light-years away from Earth.

"These features are almost certainly the result of young planet like bodies that are being formed in the disk," ALMA deputy director Stuartt Corder said in a statement. "This is surprising, since HL Tau is no more than a million years old and such young stars are not expected to have large planetary bodies capable of producing the structures we see in this image." [Amazing ALMA Radio Telescope Images]

The stunning detail and clarity of the new ALMA radio telescope image surprised scientists.

These discoveries are important, because of the belief that our solar system and planet is in some way unique in our universe. Considering the number of earth like planets and solar systems being observed is increasing just in our galaxy it becomes more and more apparent our solar system is not unique.

rwatts
11-08-2014, 06:25 PM
A couple more to throw into the mix. The first concerns researchers beginning to make definitive measurements of magnetic fields around very young stars. The second is about possible planet formation in a multiple star system.




Spatially resolved magnetic field structure in the disk of a T Tauri star, Nature 514, 597–599 (30 October 2014) 



"Magnetic fields in accretion disks play a dominant part during the star formation process1, 2 but have hitherto been observationally poorly constrained. Field strengths have been inferred on T Tauri stars3 and possibly in the innermost part of their accretion disks4, but the strength and morphology of the field in the bulk of a disk have not been observed. Spatially unresolved measurements of polarized emission (arising from elongated dust grains aligned perpendicularly to the field5) imply average fields aligned with the disks6, 7. Theoretically, the fields are expected to be largely toroidal, poloidal or a mixture of the two1, 2, 8, 9, 10, which imply different mechanisms for transporting angular momentum in the disks of actively accreting young stars such as HL Tau (ref. 11). Here we report resolved measurements of the polarized 1.25-millimetre continuum emission from the disk of HL Tau. The magnetic field on a scale of 80*astronomical units is coincident with the major axis (about 210 astronomical units long12) of the disk. From this we conclude that the magnetic field inside the disk at this scale cannot be dominated by a vertical component, though a purely toroidal field also does not fit the data well. The unexpected morphology suggests that the role of the magnetic field in the accretion of a T Tauri star is more complex than our current theoretical understanding." (http://www.nature.com/nature/journal/v514/n7524/full/nature13850.html)



The introduction and conclusion are as follows:-





First paragraph in main article
HL Tau is located 140*pc away13, in the Taurus molecular cloud. Although HL Tau is a T Tauri star, it is considered to be in an early stage of development owing to its bipolar outflow14 and possible residual envelope15. Observations and modelling of this protostar assuming a thick, flared disk suggest a stellar mass of ~0.55 times the solar mass (  ) and a disk mass of 0.14*  (ref.12). A possible planet forming in the disk of HL Tau has been observed16, though this detection was not confirmed12. However, the disk of HL Tau is gravitationally unstable, which could favour fragmentation into Jupiter-mass planets12, 16. HL Tau has the brightest disk of any T Tauri star at millimetre wavelengths, allowing observations of the fractional polarization (P) to have the best possible sensitivity. Previous observations of the polarization of the disk of HL Tau yielded marginally significant, spatially unresolved polarization detections with the James Clerk Maxwell Telescope (JCMT; polarization P = 3.6**2.4% at 14″ = 1,960*astronomical units (AU) resolution)6 and the Submillimetre Array (SMA; polarization P = 0.86**0.4% at 2″ = 280*AU resolution, archival observations released in this Letter). In addition, observations of HL Tau with the Combined Array for Millimeter-wave Astronomy (CARMA) have shown that the interferometric emission comes entirely from the disk with no contamination from large-scale envelope emission12. HL Tau is therefore a very promising source to search for a spatially resolved polarization detection.


Last paragraph
Until now, we have been unable to observationally constrain the magnetic field morphology in disks. Along with the Class 0 source IRAS 16293–2422 B, our observations of HL Tau show that a toroidal field component may last from the low-mass protostar’s initial formation to the T Tauri star stage—approximately the first 106*years of a protostar’s life26. The apparent absence of vertical fields in these observations implies that magnetocentrifugal winds driven along large-scale poloidal magnetic fields27 are probably not the dominant mechanism for redistributing the disk’s angular momentum during the accretion process of a star at the 80*AU size-scale of our observations. However, the morphology detected in HL Tau also cannot be fully explained by a simple mix of toroidal and vertical components, requiring future observations at both large scale and small scale to truly understand the role of magnetic fields in the formation of solar systems like our own.


Then there is this:-



Possible planet formation in the young, low-mass, multiple stellar system GG Tau A Nature 514, 600–602 (30 October 2014)



"The formation of planets around binary stars may be more difficult than around single stars1, 2, 3. In a close binary star (with a separation of less than a hundred astronomical units), theory predicts the presence of circumstellar disks around each star, and an outer circumbinary disk surrounding a gravitationally cleared inner cavity around the stars4, 5. Given that the inner disks are depleted by accretion onto the stars on timescales of a few thousand years, any replenishing material must be transferred from the outer reservoir to fuel planet formation (which occurs on timescales of about one million years). Gas flowing through disk cavities has been detected in single star systems6. A circumbinary disk was discovered around the young low-mass binary system GG Tau A (ref. 7), which has recently been shown to be a hierarchical triple system8. It has one large inner disk9 around the single star, GG Tau Aa, and shows small amounts of shocked hydrogen gas residing within the central cavity10, but other than a single weak detection11, the distribution of cold gas in this cavity or in any other binary or multiple star system has not hitherto been determined. Here we report imaging of gas fragments emitting radiation characteristic of carbon monoxide within the GG Tau A cavity. From the kinematics we conclude that the flow appears capable of sustaining the inner disk (around GG Tau Aa) beyond the accretion lifetime, leaving time for planet formation to occur there. These results show the complexity of planet formation around multiple stars and confirm the general picture predicted by numerical simulations." (http://www.nature.com/nature/journal/v514/n7524/full/nature13822.html)



First paragraph in main article
The triple stellar system GG Tau A consists of a single star GG Tau Aa and a close binary GG Tau Ab (with individual stars named Ab1 and Ab2). The system is 1–5 million years old12, 13, and is located 140*pc from Earth in a hole of the Taurus molecular cloud. Its molecular emission is free of contamination14 and there is no known outflow or jet associated with the source. GG Tau Aa and Ab have an apparent separation of 35*astronomical units (AU) while the separation of GG Tau Ab1 and Ab2 is 4.5*AU (ref. 8). The outer Keplerian disk of gas and dust surrounding GG Tau A (called the circumbinary disk for simplicity) consists of a ring extending from radius r*≈*190*AU to r*≈*280*AU and an outer disk extending up to 800*AU from the central stars with a total mass of ~0.15  (ref. 14; here  is the solar mass).


Last paragraph
Our observations demonstrate that active replenishment from the outer disk can sustain the circumstellar disk surrounding GG Tau Aa for a time exceeding the accretion lifetime, increasing its potential for planet formation. The presence of a condensation at the outer edge of the ring is puzzling, and needs further investigation to determine its links with accretion processes and possible planet formation. Since almost half of Sun-like stars were born in multiple systems24, our observations provide a step towards understanding the true complexity of protoplanetary disks in multiple stellar systems and unveiling planet formation mechanisms for a significant fraction of stellar systems in our Galaxy.

shunyadragon
11-09-2014, 04:15 AM
A couple more to throw into the mix. The first concerns researchers beginning to make definitive measurements of magnetic fields around very young stars. The second is about possible planet formation in a multiple star system.




Spatially resolved magnetic field structure in the disk of a T Tauri star, Nature 514, 597–599 (30 October 2014) 



"Magnetic fields in accretion disks play a dominant part during the star formation process1, 2 but have hitherto been observationally poorly constrained. Field strengths have been inferred on T Tauri stars3 and possibly in the innermost part of their accretion disks4, but the strength and morphology of the field in the bulk of a disk have not been observed. Spatially unresolved measurements of polarized emission (arising from elongated dust grains aligned perpendicularly to the field5) imply average fields aligned with the disks6, 7. Theoretically, the fields are expected to be largely toroidal, poloidal or a mixture of the two1, 2, 8, 9, 10, which imply different mechanisms for transporting angular momentum in the disks of actively accreting young stars such as HL Tau (ref. 11). Here we report resolved measurements of the polarized 1.25-millimetre continuum emission from the disk of HL Tau. The magnetic field on a scale of 80*astronomical units is coincident with the major axis (about 210 astronomical units long12) of the disk. From this we conclude that the magnetic field inside the disk at this scale cannot be dominated by a vertical component, though a purely toroidal field also does not fit the data well. The unexpected morphology suggests that the role of the magnetic field in the accretion of a T Tauri star is more complex than our current theoretical understanding." (http://www.nature.com/nature/journal/v514/n7524/full/nature13850.html)



The introduction and conclusion are as follows:-






Then there is this:-



Possible planet formation in the young, low-mass, multiple stellar system GG Tau A Nature 514, 600–602 (30 October 2014)



"The formation of planets around binary stars may be more difficult than around single stars1, 2, 3. In a close binary star (with a separation of less than a hundred astronomical units), theory predicts the presence of circumstellar disks around each star, and an outer circumbinary disk surrounding a gravitationally cleared inner cavity around the stars4, 5. Given that the inner disks are depleted by accretion onto the stars on timescales of a few thousand years, any replenishing material must be transferred from the outer reservoir to fuel planet formation (which occurs on timescales of about one million years). Gas flowing through disk cavities has been detected in single star systems6. A circumbinary disk was discovered around the young low-mass binary system GG Tau A (ref. 7), which has recently been shown to be a hierarchical triple system8. It has one large inner disk9 around the single star, GG Tau Aa, and shows small amounts of shocked hydrogen gas residing within the central cavity10, but other than a single weak detection11, the distribution of cold gas in this cavity or in any other binary or multiple star system has not hitherto been determined. Here we report imaging of gas fragments emitting radiation characteristic of carbon monoxide within the GG Tau A cavity. From the kinematics we conclude that the flow appears capable of sustaining the inner disk (around GG Tau Aa) beyond the accretion lifetime, leaving time for planet formation to occur there. These results show the complexity of planet formation around multiple stars and confirm the general picture predicted by numerical simulations." (http://www.nature.com/nature/journal/v514/n7524/full/nature13822.html)

Thank you! Good references.