Protostellar Feedback Halts the Growth
of the First Stars in the Universe

Takashi Hosokawa (1,2), Kazuyuki Omukai (2), Naoki Yoshida (3), Harold W. Yorke (1)

1: Jet Propulsion Laboratory, California Institute of Technology,
2: Department of Physics, Kyoto University,
3: Institute for the Physics and Mathematics of the Universe, TODIAS, The University of Tokyo


The first stars fundamentally transformed the early Universe by emitting the first light and by producing the first heavy elements. These effects were predetermined by the mass distribution of the first stars, which is thought to have been fixed by a complex interplay of gas accretion and protostellar radiation. We performed radiation-hydrodynamics simulations that followed the growth of a primordial protostar through to the early stages as a star with thermo-nuclear burning. The circumstellar accretion disk was evaporated by ultraviolet radiation from the star when its mass was 43 times that of the Sun. Such massive primordial stars, in contrast to the often postulated extremely massive stars, may help explain the fact that there is no signatures of the pair-instability supernovae in abundance patterns of metal-poor stars in our galaxy.

published in Science Express on November 10th 2011.
abstract reprint

manuscript including Supporting Online Material

CONTACT: hosokwtk_at_gmail.com, hosokawa_at_tap.scphys.kyoto-u.ac.jp (_at_ --> @)

Background and Motivation

It is widely believed that the first stars were formed when the age of the universe was a few hundred million years old. At its birth, a first star is just a tiny embryo - a protostar - with a mass of about one percent of the sun (see the figure below). The protostar is then expected to grow by accumulating the surrounding hot gas, but how much gas it can acquire has been largely unknown. This study revealed the entire process of the star's growth over a hundred thousand years until it became a real shining star through nuclear burning.

The Protostellar Feedback Halts the Growth: First Stars Heavy but not Monstrous

Astrophysicists thought so far that the first stars could grow huge, as much as a few hundred times the sun in mass. However, our study presents that the star regulates its own growth by emitting intensive radiation. The computer simulations showed us highly dynamical features of this process (see the figures and movies below). When the star became as large as 20 times that of the sun, it shined very bright, almost equivalent to a cluster of a hundred thousand of sun-like stars. Ultra-violet light from the luminous star then quickly heated up the gas in the vicinity to above ten thousand degrees in temperature. The hot bubble launched a high speed gas flow outward, which eventually evacuated the surrounding "parent" gas cloud from which the star was born. There remained a star with a mass of 43 times that of the sun.

Movies: 1 2 (from a different angle) 3 (from a different angle) 4 (2-dimensional slice) 5 (central region of 3000 AU)

images and videos credit: NASA / JPL-Caltech / Kyoto Univ.

Solution of a Long-standing Mystery

Our numerical simulations showed us the very exciting evolution of the first stars in the deep universe beyond our observations. However, observers have found signatures of the first stars in the elemental abundances of very old stars in our Galaxy (see the figure below). They searched for the signatures of the "monstrous" stars of hundreds of solar-masses, but could not find them. Instead, recent observations all support that the first stars should have been the massive stars of several tens of solar-masses. Such ordinary massive stars, in the sense there are indeed such stars with similar masses in the present-day Universe, are really resulting from our simulations. We provide a solution for the long-standing problem and now successfully propose a novel theoretical model of the evolution of the universe at its infancy.


+ link to the article (Science Express)
+ IPMU News
+ NASA JPL release