Massive protostar keeps growing

Discussion in 'Astronomy, Exobiology, & Cosmology' started by paddoboy, Feb 28, 2020.

  1. paddoboy Valued Senior Member

    Messages:
    27,543
    https://phys.org/news/2020-02-massive-protostar-ionization-ultraviolet.html

    Massive protostar keeps growing despite ionization heating by ultraviolet light:

    A gigantic embryonic star is still getting bigger, even though it propels vast plumes of hot gas away from itself, RIKEN astronomers have found. The discovery could help to solve an enduring mystery about how massive stars grow so large.

    Young protostars put on weight by gathering matter from a dense disk of gas and dust that swirls around them (Fig. 1). But once protostars grow beyond a certain size, further accretion is hampered by the light they emit. This may happen when ultraviolet light strips electrons from atoms in the surrounding disk to produce a hot ionized plasma that evaporates from the star, a process called photoevaporative outflow.

    Theoretical calculations have suggested that this and related factors are too weak to stop accretion. But there is insufficient observational evidence to back this up, not least because the most massive protostars are rare and very distant from the Earth.
    more at link.....

    the paper:
    https://iopscience.iop.org/article/10.3847/2041-8213/ab5309

    Discovery of a Photoionized Bipolar Outflow toward the Massive Protostar G45.47+0.05:

    Abstract:
    Massive protostars generate strong radiation feedback, which may help set the mass that they achieve by the end of the accretion process. Studying such feedback is therefore crucial for understanding the formation of massive stars. We report the discovery of a photoionized bipolar outflow toward the massive protostar G45.47+0.05 using high-resolution observations at 1.3 mm with the Atacama Large Millimeter/Submillimeter Array (ALMA) and at 7 mm with the Karl G. Jansky Very Large Array (VLA). By modeling the free–free continuum, the ionized outflow is found to be a photoevaporation flow with an electron temperature of 10,000 K and an electron number density of ~1.5 × 107 cm−3 at the center, launched from a disk of radius of 110 au. H30α hydrogen recombination line emission shows strong maser amplification, with G45 being one of very few sources to show such millimeter recombination line masers. The mass of the driving source is estimated to be 30–50 M ⊙ based on the derived ionizing photon rate, or 30–40 M ⊙ based on the H30α kinematics. The kinematics of the photoevaporated material is dominated by rotation close to the disk plane, while accelerated to outflowing motion above the disk plane. The mass loss rate of the photoevaporation outflow is estimated to be ~(2–3.5) × 10−5 M ⊙ yr−1. We also found hints of a possible jet embedded inside the wide-angle ionized outflow with nonthermal emissions. The possible coexistence of a jet and a massive photoevaporation outflow suggests that, in spite of the strong photoionization feedback, accretion is still ongoing.


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    similar story:

    https://phys.org/news/2020-02-physicists-supernovae-result-pulsating-supergiants.html

    Physicists model the supernovae that result from pulsating supergiants like Betelgeuse:

    Betelgeuse has been the center of significant media attention lately. The red supergiant is nearing the end of its life, and when a star over 10 times the mass of the Sun dies, it goes out in spectacular fashion. With its brightness recently dipping to the lowest point in the last hundred years, many space enthusiasts are excited that Betelgeuse may soon go supernova, exploding in a dazzling display that could be visible even in daylight.

    While the famous star in Orion's shoulder will likely meet its demise within the next million years—practically couple days in cosmic time—scientists maintain that its dimming is due to the star pulsating. The phenomenon is relatively common among red supergiants, and Betelgeuse has been known for decades to be in this group.
    more at link.....

    the paper:

    https://iopscience.iop.org/article/10.3847/1538-4357/ab7205


    A Massive Star's Dying Breaths: Pulsating Red Supergiants and Their Resulting Type IIP Supernovae:

    Abstract
    Massive stars undergo fundamental mode and first overtone radial pulsations with periods of 100–1000 days as red supergiants (RSGs). At large amplitudes, these pulsations substantially modify the outer envelope's density structure encountered by the outgoing shock wave from the eventual core collapse of these

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    stars. Using Modules for Experiments in Stellar Astrophysics (MESA), we model the effects of fundamental mode and first overtone pulsations in the RSG envelopes and the resulting Type IIP supernovae (SNe) using MESA+STELLA. We find that, in the case of fundamental mode pulsations, SN plateau observables, such as the luminosity at day 50, L 50; time-integrated shock energy, ET; and plateau duration, t p, are consistent with radial scalings derived considering explosions of nonpulsating stars. Namely, most of the effect of the pulsation is consistent with the behavior expected for a star of a different size at the time of explosion. However, in the case of overtone pulsations, the Lagrangian displacement is not monotonic. Therefore, in such cases, excessively bright or faint SN emission at different times reflects the underdense or overdense structure of the emitting region near the SN photosphere.



     
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  3. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

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    help set the mass

    If only we could harness such a system for preventing morbid obesity

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