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Evidence for Planets in Protoplanetary Disks

Using a near-infrared spectrograph attached to ESO’s Very Large Telescope, astronomers have been able to examine the inner protoplanetary disks around three interesting stars, with results showing the sheer diversity of the apparently emerging systems. Only a few million years old, all three stars could be considered analogs of our own Sun, going through processes like those that produced the Solar System some 4.6 billion years ago. The disks under study show regions where the dust has been cleared out, the possible signature of planetary influence.

The new work, which offers higher resolution than was earlier available, demonstrates that the previously known gaps in the dust still contain molecular gas, an indication that the dust has begun to form planetary embryos or that a planet has already formed and is clearing the disk gas as it orbits. The likely planets include a massive gas giant orbiting the star SR 21 at a distance of something less than 3.5 AU, and a possible planet around HD 135344B between 10 and 20 AU. The third star, TW Hydrae, may also show the development of one and possibly two planets. In the words of Klaus Pontoppidan (Caltech):

“Our observations with the CRIRES instrument on ESO’s Very Large Telescope clearly reveal that the disks around these three young, Sun-like stars are all very different and will most likely result in very different planetary systems.”

Image: Astronomers have been able to study planet-forming disks around young Sun-like stars in unsurpassed detail, using ESO’s Very Large Telescope. The studied disks were known to have gaps (represented by the brownish color in the image) but the astronomers found that gas is still present inside these gaps (represented by the white color in the image). This can either mean that the dust has clumped together to form planetary embryos, or that a planet has already formed and is in the process of clearing the gas in the disk. Credit: European Southern Observatory.

The techniques on display here, collectively called ‘spectro-astrometric imaging,’ are dazzling, allowing the researchers to see into the inner disk regions around stars that are more than 200 light years away, measuring distances down to one-tenth of an AU while simultaneously measuring the velocity of the gas. The disks themselves are about 100 AU across. Chalk up yet another win for adaptive optics, as the CRIRES spectrograph is fed by an AO module that corrects for atmospheric blurring, allowing high resolution. As good as these results are, they’ll be surpassed not many years from now by the ALMA (Atacama Large Millimeter/submillimeter) Array, whose operations commence in 2012.

Addendum: andy has passed along the link to the paper on this work, which is Pontoppidan et al., “Spectro-astrometric imaging of molecular gas within protoplanetary disk gaps,” accepted for publication in the Astrophysical Journal. The original ESO news release is here.

Comments on this entry are closed.

  • andy September 15, 2008, 11:33

    There seem to be quite a few disks showing evidence for planets – the most famous one being Beta Pictoris, where quite a few lines of evidence point to a planet at about 12 AU, and possibly a couple of others further out as well.

    Regarding this news story, the original press release is available from ESO here, and the original paper is on arXiv here.

  • Administrator September 15, 2008, 13:42

    Thanks, andy — both links now inserted into the text as an addendum.

  • Adam September 15, 2008, 17:37

    Hi All

    Then there’s this interesting news bite First Exoplanet Image around normal star …an 8 Jupiter mass object some 330 AU from a 5 million year old star. They’ve still got to prove it’s co-moving but it might be the real deal.

    Such distances from the central star seem inexplicable in the normal cosmogonic scenarios, but Anthony Whitworth and colleagues have developed a massive disk collapse model which forms brown dwarfs and super-jovians quite readily… Brown dwarf formation by gravitational fragmentation of massive, extended protostellar discs …a long way from the central star. Conversely what it doesn’t do is make planets further in.

    Perhaps at least two processes are making planets and brown dwarfs?

  • James M. Essig September 15, 2008, 21:16

    Hi Folks;

    It is interesting to see this evidence of the formation of proto-planetary disks.

    Looking at such disk from afar, we realize that we might be viewing the star stuff that will eventually be incorporated into the bodies of future ETI beings which might survive to reach an incredible level of evolution and advancement. We humble humans who have not yet ventured out among the stars can, in a sense feel, a certain sense of honor and nobility to be in such a position to observe such. Although I have no children, at least none that I am aware of, I kind of feel the fatherly paternal instinct when I think about these proto-planetary disks in such a way, much as a human father would contemplate the wonders and joy of the potential life full of dreams of a just conceived child or a new born. In a way, we can view our selves as the elder brothers and sisters of ETI beings and civilizitions yet to develop from star-stuff.

    A really good use for the ever increasing power of our super computers is to model stellar formation and proto-planetary disks with finer grained or finer celled grid or matrix algorithms. I think the computational fluid dynamicists, the finite element analysis folks, and the computational electro-magneto-plasma-hydrodynamics folks etc., who develop models and code to model these sorts of things will end up having an insatiable appetite for ever more powerful supercomputers. By the way, I think I have mentioned it before, perhaps a little prematurely, but I think Peta-flops supercomputers computers are finally here or in the process of physical assembly. This stuff is just plain cool!



  • andy September 16, 2008, 11:53

    Adam: that’s an interesting paper… it also has implications for interpreting systems like 2M1207 which appear to have jovian-mass objects in orbit around brown dwarf primaries.

  • Adam September 16, 2008, 18:10

    Hi andy

    Very interesting paper. I’ve followed Whitworth’s work for years – tidally initiated planet and brown dwarf formation between protoplanetary disks seems well supported by the data, and Whitworth’s work keeps underlining the fact that stars don’t form alone, that tidal disruption plays an underappreciated role in cosmogony.

    At the other end of the size spectrum there’s a lot of work focussed on how dust turns into planetesimals – gas-drag quickly drops anything below ~km size straight into the star within ~100 years, so the time constraint is very tight. Gravitational collapse from dust to planetesimals seems the only option, but the success at modelling the process has been ambivalent. Phil Armitage and colleagues have managed to get collapse in their models, thanks to spiral waves forming in the dust-gas mix, but it’s still a very uncertain solution to the puzzle.

    What that particular model means is that metallicity drives the efficiency of formation of planetesimals and below a certain level nothing forms planetesimals. Thus in low metallicity systems planets can only form via the direct collapse process, and thus would only form terrestrial planets very inefficiently via stripped cores produced from collisions, or escaped moons.