Massive Stars Start Life Big… Really BIG!

Article written: 10 Dec , 2011
Updated: 24 Dec , 2015
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It might be hard to believe, but massive stars are larger in their infant stage than they are when fully formed. Thanks to a team of astronomers at the University of Amsterdam, observations have shown that during the initial stages of creation, super-massive stars are super-sized. This research now confirms the theory that massive stars contract until they reach the age of equilibrium.

In the past, one of the difficulties in proving this theory has been the near impossibility of getting a clear spectrum of a massive star during formation due to obscuring dust and gases. Now, using the powerful spectrograph X-shooter on ESO’s Very Large Telescope in Chile, researchers have been able to obtain data on a young star cataloged as B275 in the “Omega Nebula” (M17). Built by an international team, the X-shooter has a special wavelength coverage: from 300 nm (UV) to 2500 nm (infrared) and is the most powerful tool of its kind. Its “one shot” image has now provided us with the first solid spectral evidence of a star on its way to main sequence. Seven times more massive than the Sun, B275 has shown itself to be three times the size of a normal main-sequence star. These results help to confirm present modeling.

When young, massive stars begin to coalesce, they are shrouded in a rotating gas disk where the mass-accretion process starts. In this state, strong jets are also produced in a very complicated mechanism which isn’t well understood. These actions were reported earlier by the same research group. When accretion is complete, the disk evaporates and the stellar surface then becomes visible. As of now, B275 is displaying these traits and its core temperature has reached the point where hydrogen fusion has commenced. Now the star will continue to contract until the energy production at its center matches the radiation at the surface and equilibrium is achieved. To make the situation even more curious, the X-shooter spectrum has shown B275 to have a measurably lower surface temperature for a star of its type – a very luminous one. This wide margin of difference can be equated to its large radius – and that’s what the results show. The intense spectral lines associated with B275 are consistent with a giant star.

Lead author Bram Ochsendorf, was the man to analyze the spectrum of this curious star as part of his Master’s research program at the University of Amsterdam. He has also began his PhD project in Leiden. Says Ochsendorf, “The large wavelength coverage of X shooter provides the opportunity to determine many stellar properties at once, like the surface temperature, size, and the presence of a disk.”

The spectrum of B275 was obtained during the X-shooter science verification process by co-authors Rolf Chini and Vera Hoffmeister from the Ruhr-Universitaet in Bochum, Germany. “This is a beautiful confirmation of new theoretical models describing the formation process of massive stars, obtained thanks to the extreme sensitivity of X-shooter”, remarks Ochsendorf’s supervisor Prof. Lex Kaper.

Original Story Source: First firm spectral classification of an early-B pre-main-sequence star: B275 in M17.

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6 Responses

  1. Ookmon says

    One of the things that I’m interested in during this accretion process is in the observation of the evaporating material gas, dust etc. that is not incorporated into this young forming star. Granted much of this material will have been, ejected upon solar winds or the outward pressures of the star collapsing when reaching nuclear fission, but in all likelihood would remain gravitationally locked to an extent as it was before the formation of the star.
    I would be interested in the likelihood of this leftover material and the possibility of it eventually lending those materials for accretion into plants. I would hypothesize that the relative masses of these embryonic stars would be proportional to the likelihood of planets and their relative masses based on the observations of this process. I would also hypothesize that the relative bands that planets may form onto are proportional to the pressure waves and their likely harmonic reactions, i.e. overlapping waves that creates a larger wave of the sum of the two, thereby creating relative patches of denser material where in which the accretion process of planets can form, and quite possibly setting the stage for the growth of plants as well as their sizes and orbital stations at the initial formation of this process.
    Another of the interesting observations are the jets of material blasting from the poles. It would seem to me in all likelihood to be a very similar action as if one were to squeeze a lemon in one’s hands. The immense pressures created along the equatorial plane and then expanding throughout the rest of the body of the star, when combined with the warping of the magnetic field created at the poles could in all likelihood produce the types of events that we observe, much like the material squeezed out of both ends of lemon as the relative pressures at the poles are less than those along the equatorial plain. I’m sure the process is much more sophisticated than that but all things being equal the simplest answers are usually correct.

    • Torbjörn Larsson says

      – Planet formation is not well understood.

      Recent results points to more planets the higher metallicity of the star, and aggregation more than collapse. Aggregation would increase planet size with more disk material (while collapse would not), which in turn would go with the mass of the star.

      A disk is a very dynamic and in some senses chaotic process with the star ejecting material that rains down on the disk and recirculates to the star. I don’t think we should expect standing waves.

      – Protostar mass losses are driven by heating under coalescence (sez my astrobiology text books).

    • Anonymous says

      “I would also hypothesize that the relative bands that planets may form onto are proportional to the pressure waves and their likely harmonic reactions, i.e. overlapping waves that create a larger wave of the sum of the two, thereby creating relative patches of denser material wherein which the accretion process of planets can [take place], and quite possibly setting the stage for the growth of planets as well as their sizes and orbital stations at the initial formation of this process.”

      That doesn’t sound like a brand-new hypothesis but more like something built upon the Lin-Shu density-wave theory put forward way back in the Sixties in order to explain the spiral structure and the bar of galaxies like the Milky Way, in which case it might share common problems with that theory, like the fact that density waves shed energy when they generate shock waves and something had to be found that revitalized them, which turned out to be the interstellar gas clouds. One would have to ask what, in the case of incipient planetary systems, replaces the dynamic role gas plays in the case of galaxies, keeps the reverberations going and eventually allows accretion to take place.

  2. Anonymous says

    ” It might be hard to believe, but massive stars are larger in their infant stage than they are when fully formed.”

    It’s even harder to believe in the case of animal species, especially if they’re vertebrates, and I know of only a single case: “Pseudis paradoxa”, the paradoxical frog or shrinking frog, whose huge tadpole can grow to be about 10 inches (25 cm.) long, then it shrinks drastically. The adult measures only one fourth as long as that, which is amazing. Maybe there are more things that will be willing to mess around with the mature frog than with the baby frog.

    There’s something else that’s odd here: why does it sound funny when it happens to a frog, but not when a star is involved??? I think I know the answer but I’ll omit it because someone might take offense, especially if afflicted with the condition called “obesity” (of the unhealthy kind). Sorry!

    • Torbjörn Larsson says

      It is just not a familiar scene among vertebrates, but almost all invertebrates would be like that I think.

      The reason is like you touch on, for all purposes except reproduction the juvenile and the adult can be like two different species. And again, especially among invertebrates. Except in such cases the adult retains the juvenile form. (Say, axolotl.)

      Unless the adult body plan constrains the juvenile, which is very much the case for vertebrates, species are free to evolve to different juvenile & adult sizes just as they differ in other traits.

      • Anonymous says

        “(…) almost all invertebrates would be like that I think.”

        Almost all invertebrates??!! It seems like the only invertebrate species with the privilege, if that’s what it is, are 1) those that go through a chrysalis stage (Lepidoptera, or butterflies and moths) and 2) sea creatures that in their early stages move around and then eventually attach themselves to a rock or some other substrate and settle down permanently. That would be more like a modest minority, wouldn’t it?

        “Since evolution puts an emphasis on successful, i.e. differential, reproduction, it may seem wasteful to have a smaller adult instead of a steady growing curve.”

        I’m not sure I understand that claim. A greater size in males generally does promote successful reproduction of individuals within a species, but we’re talking, not about individual differences in size at a certain stage in the life cycle of a species (the adut stage) but about the difference in size between individuals belonging to two stages. Why would a species as a whole necessary have to benefit more if the adults are bigger than the young ones? Wouldn’t that depend on a combination of factors linked to the environment?

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