Second-generation stars identified, giving clues about their predecessors

Second-generation stars identified, giving clues about their predecessors
The figure shows a sub-population of ancient stars, called Carbon-Enhanced Metal-Poor (CEMP) stars. These stars contain 100 to 1,000,000 times LESS iron (and other heavy elements) than the Sun, but 10 to 10,000 times MORE carbon, relative to iron. The unusual chemicalcompositions of these stars provides clues to their birth environments, and the nature of the stars in which the carbon formed. In the figure, A(C) is the absolute amount of carbon, while the horizontal axis represents the ratio of iron, relative to hydrogen, compared with the same ratio in the Sun. Credit: University of Notre Dame

University of Notre Dame astronomers have identified what they believe to be the second generation of stars, shedding light on the nature of the universe's first stars.

A subclass of carbon-enhanced metal-poor (CEMP) , the so-called CEMP-no stars, are ancient stars that have large amounts of carbon but little of the (such as iron) common to later-generation stars. Massive first-generation stars made up of pure hydrogen and helium produced and ejected by stellar winds during their lifetimes or when they exploded as supernovae. Those metals—anything heavier than helium, in astronomical parlance—polluted the nearby from which new stars formed.

Jinmi Yoon, a postdoctoral research associate in the Department of Physics; Timothy Beers, the Notre Dame Chair in Astrophysics; and Vinicius Placco, a research professor at Notre Dame, along with their collaborators, show in findings published in the Astrophysics Journal this week that the lowest metallicity stars, the most chemically primitive, include large fractions of CEMP stars. The CEMP-no stars, which are also rich in nitrogen and oxygen, are likely the stars born out of hydrogen and helium gas clouds that were polluted by the elements produced by the universe's first stars.

"The CEMP-no stars we see today, at least many of them, were born shortly after the Big Bang, 13.5 billion years ago, out of almost completely unpolluted material," Yoon says. "These stars, located in the halo system of our galaxy, are true second-generation stars—born out of the nucleosynthesis products of the very first stars."

Beers says it's unlikely that any of the universe's first stars still exist, but much can be learned about them from detailed studies of the next generation of stars.

"We're analyzing the chemical products of the very first stars by looking at what was locked up by the second-generation stars," Beers says. "We can use this information to tell the story of how the first elements were formed, and determine the distribution of the masses of those first stars. If we know how their masses were distributed, we can model the process of how the first stars formed and evolved from the very beginning."

The authors used high-resolution spectroscopic data gathered by many astronomers to measure the chemical compositions of about 300 stars in the halo of the Milky Way. More and heavier elements form as later generations of stars continue to contribute additional metals, they say. As new generations of stars are born, they incorporate the metals produced by prior generations. Hence, the more heavy metals a star contains, the more recently it was born. Our sun, for example, is relatively young, with an age of only 4.5 billion years.

A companion paper, titled "Observational constraints on first-star nucleosynthesis. II. Spectroscopy of an ultra metal-poor CEMP-no star," of which Placco was the lead author, was also published in the same issue of the journal this week. The paper compares theoretical predictions for the chemical composition of zero-metallicity supernova models with a newly discovered CEMP-no star in the Milky Way galaxy.

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More information: Jinmi Yoon et al. OBSERVATIONAL CONSTRAINTS ON FIRST-STAR NUCLEOSYNTHESIS. I. EVIDENCE FOR MULTIPLE PROGENITORS OF CEMP-NO STARS, The Astrophysical Journal (2016). DOI: 10.3847/0004-637X/833/1/20

Vinicius M. Placco et al. OBSERVATIONAL CONSTRAINTS ON FIRST-STAR NUCLEOSYNTHESIS. II. SPECTROSCOPY OF AN ULTRA METAL-POOR CEMP-no STAR, The Astrophysical Journal (2016). DOI: 10.3847/0004-637X/833/1/21

Journal information: Astrophysical Journal

Citation: Second-generation stars identified, giving clues about their predecessors (2016, December 6) retrieved 23 September 2019 from
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User comments

Dec 06, 2016
"Those metals—anything heavier than helium, in astronomical parlance—polluted the nearby gas clouds from which new stars formed."

So now we have pollution in the cosmos? Negative connotation, much?

Dec 06, 2016
Think of it as recycling...

Dec 07, 2016
The allusion to the article.
The Earth has more Fe of gaseous and other planets and bodies in general, therefore, the Earth is njmlađe body in the Universe! Saturn is the oldest body, the first generation after the Big Bang because "Despite consisting mostly of hydrogen and helium," Wiki

Whether believe the authors of articles in what they are written?

Dec 07, 2016
Not much above carbon was made by first gen stars? We are invited to speculate that the first generation stars didn't produce many supernovae, then?

I'm trying to imagine why, in a smaller universe and given pristine, relatively dense hydrogen clouds from the Big Bang, the first generation stars weren't, on average, much larger than the average star is today.

If first-gen stars tended to be small, then what's the expected residue? A lot of spun-down neutron stars?

Meh. I can't even imagine how to detect spun-down neutron stars. If they aren't rotating rapidly, they aren't strobing powerful emissions we can detect.

Dec 08, 2016
One of many things I find curious with our current understanding of the cosmos is the lack of heavier elements during the creation of the universe. The current theory is that the really heavy elements like gold, osmium, ect. cannot be produced in a large star supernova because they don't produce enough energy for the fusion those elements. Such elements require the much higher energy levels of two neutron stars merging. Now that's all find and good but the 'big bang' had many orders of magnitude higher energy than merging neutron stars so why didn't heavy elements form when matter 'precipitated' out?

Dec 09, 2016
It is not just about the total energy. See for a brief discussion of the topic.

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