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TOPIC: The first stars


L

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dark star
Credit: The University of Utah

This artist's conception shows what an invisible "dark star" might look like when viewed in infrared light that it emits as heat. The core is enveloped by clouds of hydrogen and helium gas. A new University of Utah study suggests the first stars in the universe did not shine, but may have been dark stars.

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Dark Matter in Newborn Universe Doused Earliest Stars
Perhaps the first stars in the newborn universe did not shine, but instead were invisible "dark stars" 400 to 200,000 times wider than the sun and powered by the annihilation of mysterious dark matter, a University of Utah study concludes.
The study - to be published next month in the journal Physical Review Letters - calculated how the birth of the first stars almost 13 billion years ago might have been influenced by the presence of dark matter - the unseen, yet-unidentified stuff that scientists believe makes up most matter in the universe.
It is conceivable that gigantic dark stars may exist today, and although they do not emit visible light, they could be detected because they should spew gamma rays, neutrinos and antimatter and be associated with clouds of cold, molecular hydrogen gas that normally wouldn't harbour such energetic particles.

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HE 1523-0901
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Astronomers have used a unique process to determine that a star in our galaxy is nearly as old as the universe itself.
The star is 13.2 billion years old, while the universe dates back 13.7 billion years, according to the European Organisation for Astronomical Research in the Southern Hemisphere (ESO).


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A groundbreaking study has provided new insight into the way the first stars were formed at the start of the Universe, some 13 billion years ago.

Cosmologists from Durham University, publishing their results in the prestigious international academic journal, Science, suggest that the formation of the first stars depends crucially on the nature of the dark matter, the strange material that makes up most of the mass in the universe.
The discovery takes scientists a step further to determining the nature of dark matter, which remains a mystery since it was first discovered more than 70 years ago. It also suggests that some of the very first stars that ever formed can still be found in the Milky Way galaxy today.

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Title: The Effect of Dark Matter on the First Stars: A New Phase of Stellar Evolution
Authors: Katherine Freese, Paolo Gondolo, Douglas Spolyar

Dark matter (DM) in protostellar halos can dramatically alter the current theoretical framework for the formation of the first stars. Heat from supersymmetric DM annihilation can overwhelm any cooling mechanism, consequently impeding the star formation process and possibly leading to a new stellar phase. The first stars to form in the universe may be "dark stars"; i.e., giant (larger than 1 AU) hydrogen-helium stars powered by DM annihilation instead of nuclear fusion. Possibilities for detecting dark stars are discussed.

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Population III stars
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Title: Population III stars: hidden or disappeared ?
Authors: L. Tornatore, A. Ferrara, R. Schneider

A PopIII/Pop II transition from massive to normal stars is predicted to occur when the metallicity of the star forming gas crosses the critical range Z_cr = 10^(-5 1) Z_sun. To investigate the cosmic implications of such process we use numerical simulations which follow the evolution, metal enrichment and energy deposition of both Pop III and Pop II stars. We find that: (i) due to inefficient heavy element transport by outflows and slow "genetic" transmission during hierarchical growth, large fluctuations around the average metallicity arise; as a result Pop III star formation continues down to z=2.5, but at a low peak rate of 10^-5 M_sun yr^-1 Mpc^-3 occurring at z~6 (about 10^-4 of the PopII one); (ii) Pop III star formation proceeds in a "inside-out" mode in which formation sites are progressively confined at the periphery of collapsed structures, where the low gas density and correspondingly long free-fall timescales result in a very inefficient astration. These conclusions strongly encourage deep searches for pristine star formation sites at moderate (2<z<5) redshifts where metal free stars are likely to be hidden.

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HE 1523-0901
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Star HE 1523-0901 lying in Libra is amongst a sample of bright metal-poor stars selected from the Hamburg-ESO Survey and whose age using various chronometers has been estimated to be 13.2 billion years old, thus making it one of the oldest known stars to date and which was created a mere 500 million years following the Big Bang. Using techniques similar to carbon-14 dating, the star's thorium and uranium abundance (amongst others) has helped establish the star's age as well as set a lower bound for the creation of the universe. This "galactic fossil" lies two degrees east of Zubeneschamali (-Lib, mag 2.57) and reaches its greatest altitude at the southern meridian during summer and around midnight.

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Position(2000) RA: 15h 26m 01.2s / Dec: -09 11' 38"

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A star, with the not-so catchy name of HE 1523-0901, that's estimated to be 13.2 billion years old (plus or minus 2 billion years) almost as old as our 13.7-billion-year-old Universe. Despite being so old, it's quite nearby; it's in our Galaxy of the Milky Way.

Did we know that stars can be that old?
Yes other really old stars have been found, such as the ancient CS 31082-001, estimated to be 14 billion years old, plus or minus 3 billion years.

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HE 1523-0901
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How old are the oldest stars? Using ESO's VLT, astronomers recently measured the age of a star located in our Galaxy. The star, a real fossil, is found to be 13.2 billion years old, not very far from the 13.7 billion years age of the Universe. The star, HE 1523-0901, was clearly born at the dawn of time.

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Oldest stars
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How old are the oldest stars? An international team of astronomers led by Dr. Anna Frebel of The University of Texas at Austin McDonald Observatory recently measured the age of an ancient star in our Milky Way galaxy at an extraordinary 13.2 billion years. This measurement provides a lower limit to the age of the universe and will help to disentangle the chemical history of our galaxy. Frebels results are published in todays edition of The Astrophysical Journal Letters.
The team used radioactive decay dating techniques to date the star, called HE 1523-0901. This is close to the age of the universe of 13.7 billion years.

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