A team of researchers, led by Miho N. Ishigaki, at the Kavli IPMU, The University of Tokyo, pointed out that the elemental abundance of the most iron-poor star can be explained by elements ejected from supernova explosions of the universe’s first stars. Their theoretical study revealed that massive stars, which are several tens of times more immense than the Sun, were present among the first stars. The presence of these massive stars has great implications on the theory of star formation in the absence of heavy elements.
Iron-poor stars provide insight about the very early universe where the first generation of stars and galaxies formed. The recent discovery of the most iron-poor star SMSS J031300.36-670839.3 (SMSS J0313-6708) was big news in early 2014, especially for astronomers working on the so-called “Galactic archaeology”.
When the universe first began, only light elements such as hydrogen and helium existed. As these first stars ended their short but wild lives, the universe became enriched with heavy elements, which are essential to form the materials found on Earth, including humans. Hence, iron-poor stars are much older than the Sun, and were born when the universe only contained trace amounts of heavy elements.
SMSS J0313-6708 is the most iron-poor star ever found. Its spectrum lacks iron absorption lines. The estimated upper limit for its iron abundance is about a ten-millionth of that of the Sun, and its iron content is about hundred times lower than the previous record for the most iron-poor star.
“We received the news of the most iron-poor star with a great excitement,” Ken’ichi Nomoto at the Kavli IPMU says, “since this star may be the oldest fossil record and may elucidate the unknown nature of the first stars.” The first stars, which formed in the early universe, likely had a large impact on their environments. For example, the strong ultra-violet light emitted by the first stars helped ionize the early universe. In addition, their supernova explosions ejected heavy elements that have helped form subsequent generations of stars and galaxies.
“The impact of these stars on the surrounding environment depends critically on their masses when they were born,” Ishigaki says. “However, direct observational constraints of the first stars’ masses are not available since most of them likely died out a long, long time ago.”
Due to its unusual chemical composition, some astrophysicists have speculated that SMSS J0313-6708 was born from the gas enriched by a first star, which has a mass 60 times that of the Sun, and synthesized a small amount of calcium through a special nucleosynthesis.
On the other hand, Ishigaki’s team focused on its very large carbon enhancement relative to iron and calcium. Previous studies by Nozomu Tominaga at Konan University/Kavli IPMU suggested that such a feature is consistent with a supernova in which the synthesized elements fall back. However, the question was whether this scenario can also explain the most extreme abundance pattern in SMSS J0313-6708, the most iron-poor star.
The team compared the observed abundances and theoretical calculations of the elements ejected by the supernova of first stars with masses 25 and 40 times that of the Sun. They concluded that the observed abundance pattern can be reproduced if stars with those masses undergo a special type of supernova in which most of the ejected matter falls back to the central remnant. A highly asymmetric explosion involving a jet-like feature should produce this type of supernova. As a consequence of the jet, iron and calcium, which are located deep inside massive stars, are ejected along with the jet, but a large fraction of the ejected material falls back along the equatorial plane. Because carbon is largely contained in the outer region, it is almost entirely ejected without falling back. This model successfully explains the low abundance of calcium, the non-detection of iron, and the high abundance of carbon observed in SMSS J0313-6708.
“If such supernovae are actually possible,” Nomoto says, “the result supports the theoretical prediction that the first stars could be typical massive stars rather than monster-like objects with masses more than several hundred times that of the Sun.” Since heavy elements play a role in star formation through the gravitational pull of interstellar gas, the first stars, which formed without heavy elements, should display quite different characteristics compared to what is typically observed in the present Milky Way Galaxy. In particular, without heavy elements, some researchers have suggested that stars could be as massive as a few hundred times that of the Sun. The presence of stars much less massive than such monster-like objects among the first stars may affect the theory of star formation in the absence of heavy elements. In future studies, researchers should employ simulations for the formation of the first stars in the early universe that reproduce the present result.
“The next issue is to determine if these less massive stars are typical first stars,” Ishigaki says. “In the near future, more data from a number of iron-poor stars will be available. Applying the method we used in this study to these data will shed light on the unknown nature of the first stars.”
Astrophysical Journal Letters (792, (2014)、32-37)
Title: Faint Population III Supernovae as the Origin of the Most Iron-poor Stars
Authors: Miho N. Ishigaki1, Nozomu Tominaga1,2, Chiaki Kobayashi1,3, and Ken'ichi Nomoto1,4
1 Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, The University of Tokyo,
2 Department of Physics, Faculty of Science and Engineering, Konan University,
3 School of Physics, Astronomy and Mathematics, Centre for Astrophysics Research, University of Hertfordshire,
4 Hamamatsu Professor
Miho Ishigaki, Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, firstname.lastname@example.org
Ken'ichi Nomoto, Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, nomoto_at_astron.s.u-tokyo.ac.jp
Marina Komori, Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
+81-4-7136-5977 (office), press_at_ipmu.jp
Aya Tsuboi, Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
Kavli IPMU (Kavli Institute for the Physics and Mathematics of the Universe) is an international research institute with English as its official language. The goal of the institute is to discover the fundamental laws of nature and to understand the Universe from the synergistic perspectives of mathematics, astronomy, and theoretical and experimental physics. The Institute for the Physics and Mathematics of the Universe (IPMU) was established in October 2007 under the World Premier International Research Center Initiative (WPI) of the Ministry of Education, Sports, Science and Technology in Japan with the University of Tokyo as the host institution. IPMU was designated as the first research institute within Todai Institutes for Advanced Study (TODIAS) in January 2011. It received an endowment from The Kavli Foundation and was renamed the “Kavli Institute for the Physics and Mathematics of the Universe” in April 2012. Kavli IPMU is located on the Kashiwa campus of the University of Tokyo, and more than half of its full-time scientific members come from outside Japan.
Kavli IPMU Website - http://www.ipmu.jp/
Marina Komori | Eurek Alert!
What happens when we heat the atomic lattice of a magnet all of a sudden?
17.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
17.07.2018 | Information Technology
17.07.2018 | Materials Sciences
17.07.2018 | Power and Electrical Engineering