Planet Formation Observed Around Massive Stars

Article written: 6 Jan , 2010
Updated: 23 Jan , 2013
by

As the old saying goes – big stars live fast and die young. And, according to new research presented at the 215th meeting of the American Astronomical Society, so do their planets.

A team of astronomers from the Harvard-Smithsonian Center for Astrophysics (CfA) and the National Optical Astronomy Observatory (NOAO) examined a star forming region called W5, which lies about 6,500 light years away in the constellation Cassiopeia, using NASA’s Spitzer Space Telescope and the ground-based Two Micron All-Sky Survey (2MASS) to look for signs of dusty planetary disks around more than 500 massive stars of A and B spectral types – which are generally between 2 and 15 solar masses.

The team found that about ten per cent of all the stars examined had dusty disks – and of these 15 stars showed signs of a central gap suggestive of a new born Jupiter-scale planet clearing its orbit.

“The gravity of a Jupiter-sized object could easily clear the inner disk out to a radius of 10 to 20 astronomical units, which is what we see,” said Lori Allen of NOAO. (An astronomical unit is the average distance between the Earth and the Sun).

The research team have also suggested that all massive stars may begin their life with a sizeable dusty disk of accreting material. However, the powerful radiation and stellar winds generated by such massive stars tend to destroy these disks rapidly. The stars observed in the W5 region are thought to be only two to five million years old, but most have already lost the dusty disk needed to make planets. On this basis, it seems that, at least for type A and B stars, planets must form quickly or not at all.

Prospects for finding life on such planets are slim. While the massive stars may foster a habitable zone of some kind – which in the case of life forms depending on liquid water as a chemical solvent, would be considerably further out from these stars than the Earth is from the Sun. However, such life forms would have limited future.

Life on Earth needed over three billion years just to evolve to the early differentiated body forms seen in the Cambrian explosion. Life on an exoplanet orbiting massive A or B type stars would have between 10 and 500 million years before its star grows to a red giant or a supernova.

“These stars aren’t good targets in the hunt for extraterrestrials,” said Xavier Koenig of the Harvard-Smithsonian CfA, who presented the research in a press conference at the AAS meeting today, “but they give us a great new way to get a better understanding of planet formation.”



12 Responses

  1. SuperKevin says

    Another great reason to search around smaller stars for earth-like planets.

  2. Torbjorn Larsson OM says

    Hm. The prospect of having life wouldn’t be any different from other cases. Presumably a few million years would do it, after enough volatiles accumulated.

    The trouble would be in finding it indeed. AFAIU a main hypothesis is that our own atmosphere went from reductive to oxidative by hydrogen loss in about 500 My. And I believe global traces of photosynthesis would show up only after that.

    So maybe a rare Earth analog would allow life detection. The rest would be crypto-biologic at best.

    Massive ocean life planets (habitable planets type IV in the Lammer et al classification) would presumably survive much longer on internal heat. The trouble right now is that we don’t know about them neither if life is possible (lack of minerals) nor detectable (lack of bio-signatures).

  3. Tauridborn says

    Being a creationist, this logic of A and B stars being unable to have habitable planets seems absurd to me. Even if the Theory of Evolution was true- which I don’t believe it is- there could still be an inhabitable planet there, perhaps with faster evolution than on Earth? It seems foolish to discount evidence based on a theory.

  4. William928 says

    Trolling, anyone? I’m ecstatic to see the number of articles related to exoplanet discovery and formation recently. Keep ’em coming! Yea Kepler!

  5. Lawrence B. Crowell says

    These planets might have some start at the game of life. The first problem I see is that these stars produce a large amount of UV and X-rays, but then conditions on the planet might shield this out. We don’t understand pre-biotic evolution, if we are to call it that, which lead to the development of life. Biological evolution does not tell us anything about this. We are faced with ignorance, but an ignorance which should have a scientific answer. Once started it only would have 100 million years or so to develop, which does not bode well for the prospects of complex life

    Creationists? Well such folks have a right to read and post here. Of course a strict creationist ideology precludes a whole lot of astrophysics and cosmology. Indeed to take it right, the fall of Adam and the expulsion from the garden meant the whole structure of reality changed. Our problems stem from the laws of thermodynamics and the competition for energy, which we encode in things like money and power. So presumably prior to then the universe had no entropy principle. Then for various reasons a God restructured everything from beyond the CMB limit to Earth because of a peccadillo committed by two people. Yeah it is a bit of a stretch to presume that because of that the laws of physics were rescripted so that energy flowed in a direction so it became less available, and further that the entire universe was restructured to appear as if it is 13.7 billion years old, in contradiction from the “clear truth” of scripture. I think it might be the other way around, in that the whole concept of God according to religious beliefs is at best skating on thin ice.

    LC

  6. Member
    IVAN3MAN says

    Being a realist, it seems more foolish to discount a theory despite the evidence.

  7. tomkaten says

    Ok, so let me get this straight. Day before yesterday we’ve discovered that planets form around brown dwarves. Yesterday, that they form aroud pulsars. Now, even around giant stars.

    Our preconception was that a planetary system was a pretty rare sight in the Universe, but now we’re beginning to see the real side of this: planets form everywhere. The day will probably come when we notice that the stars not having planets are the exception in this case.

    And isn’t it natural that they form around most stars ? The same physical laws that acted here are in effect everywhere else. There’s a lot of matter left when a star is born. Where’s it going to accumulate if not in planets ?

    I’m not trying to prove anything, just wondering…

  8. Torbjorn Larsson OM says

    Some off the cuff reactions, while I’m waiting for the air outside to thaw ;-):

    The first problem I see is that these stars produce a large amount of UV and X-rays, […] We don’t understand pre-biotic evolution,

    We understand pre-biotic evolution well enough to have predictive theories that passes many tests. The ZnS world is one of them, and coincidentally it requires UV (and radiation) for initial photo-selection in the same way that PAH formation on interstellar dust requires it.

    The downside is that it is a path for CO2/water atmosphere planets, as the UV goes into synthesizing formic acid from CO2 on near surface hydrothermal ZnS deposits to turn the photo-selection crank on bio-compounds.

    The old FeS deep hydrothermal deposit theory can’t manage either of those, the redox potential is too low beyond sparse CO synthesizing, so it is a less likely path to life. Nor has it been rigidly tested what I know of. Which is troublesome when we turn from habitable planets type I (CO2/water/tectonics) to other types.

    The day will probably come when we notice that the stars not having planets are the exception in this case.

    Another addition, the other week there was this article about a distinct planetary IR signature turning up in galaxy surveys, between the usual star and dust signatures.

    The day will probably come when we notice that the galaxies not having planets are the exception in this case.

    Even if the Theory of Evolution was true- there could still be an inhabitable planet there,

    Habitability depends on bioproductivity (evolution), but having acquired biology, being inhabited, depends on abiogenesis (not evolution). In analogy, what you are claiming is that rocks (mass) will fall even if there never was any rocks (mass) in the first place.

    But evolution isn’t the theory about how to acquire life in the first place, any more than gravity is the theory how particles come to acquire mass in the first place. Acquiring life is abiogenesis, acquiring mass is Standard Model (Higg’s mechanism).

    It seems foolish to discount evidence based on a theory.

    It seems foolish to discount that its evidence is part of any theory. A theory is a set of facts interconnected by prediction, so it is a “super-fact”, often known to be more real than any isolated fact.

    For example, evolution predicts so much that not only is it tested beyond reasonable doubt, there is no longer doubt at all that any other theory can replace it. Mundane facts aren’t known to such qualitative certainty as the fact of having a unique well-tested theory.

  9. Torbjorn Larsson OM says

    Oops:

    “”Even if the Theory of Evolution was true- there could still be an inhabitable planet there,”” – “Even if the Theory of Evolution was true- […] there could still be an inhabitable planet there,”

    Also, I meant to add this mirroring of the definition of abiogenesis/Higg’s mechanism with definitions of evolution/gravity:

    How living populations change over time under interaction with the environment is a general definition of evolution, how mass-energy change over time under interaction with space-time is a general definition of gravity (as in general relativity).

    [And in both cases the environment changes from these interactions as well. Highly non-linear processes both.]

  10. Olaf says

    @Torbjorn Larsson

    Nice explanation!

  11. Olaf says

    @Tauridborn

    You do not have to believe in evolution, you can actually test it. Read some books, set up a lab experiment and start testing away.

  12. Lawrence B. Crowell says

    @ Olaf, Right evolution is not a belief system, but a theory which is backed by observation and evidence. Biological evolution is supported by a huge preponderance of evidence. No need for belief, but a huge weight of facts back it up.

    LC

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