Fossil Galaxy May Be One of First Ever Formed

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The stars in the nearby Segue 1 dwarf galaxy have fewer metals than any other galaxy known, suggesting the object is a relic from the baby universe.

A tiny galaxy circling the Milky Way may be a fossil left over from the early universe, astronomers say. A recent study found that the stars in the galaxy, called Segue 1, contain fewer heavy elements than those of any other galaxy known, implying that the object may have stopped evolving almost 13 billion years ago. If true, Segue 1 could offer a window into the conditions of the early universe and reveal how some of the first galaxies came to be.
 
Segue 1 is very, very tiny. It appears to contain only a few hundred stars, compared with the few hundred billion stars in the Milky Way Galaxy. Researchers led by Anna Frebel of the Massachusetts Institute of Technology collected detailed information on the elemental composition of six of the brightest of Segue 1’s stars using the Las Campanas Observatory’s Magellan Telescopes in Chile and the Keck Observatory in Hawaii. The measurements, reported in a paper accepted for The Astrophysical Journal, revealed that these stars are made almost entirely of hydrogen and helium, and contain just trace amounts of heavier elements such as iron. No other galaxy studied holds so few heavy elements, making Segue 1 the “least chemically evolved galaxy known.”
 
Complex elements are forged inside the cores of stars by the nuclear fusion of more basic elements such as hydrogen and helium atoms. When stars explode in supernovae, even heavier atoms are created. elements spew into space to infuse the gas that births the next generation of stars, so that each successive generation contains more and more heavy elements, known as metals. “Segue 1 is so ridiculously metal-poor that we suspect at least a couple of the stars are direct descendants of the first stars ever to blow up in the universe,” says study co-author Evan Kirby of the University of California, Irvine.
 
All supernovae are not created equal. When very massive stars blow up they form a mix of elements such as magnesium and calcium, whereas low-mass star explosions almost exclusively make iron. Frebel and her colleagues measured the content of each of these particular elements in Segue 1’s stars and found that they contained the products of high-mass stars but very few products of low-mass stars. Because high-mass stars die much younger than do low-mass ones, this evidence reveals how quickly star formation occurred in the dwarf galaxy. “Segue 1 is the only example that we know of now that was never enriched by these low-mass stars, meaning it formed stars really quickly, in the blink of an eye,” Kirby says. “If it had formed stars long enough those low-mass stars would have to contribute.”
 
The findings suggest Segue 1 went through one brief bout of star formation long ago, and then stopped forever. “The big question is, why did it stop?” says U.C. Irvine astrophysicist James Bullock, who was not involved in the study. “A galaxy like this should have been able to make a million more stars, but it didn’t.”

Written By: Clara Moskowitz
continue to source article at scientificamerican.com

7 COMMENTS

  1. @OP- All supernovae are not created equal. When very massive stars blow up they form a mix of elements such as magnesium and calcium, whereas low-mass star explosions almost exclusively make iron.

    Just to make a simple point – All heavy elements (beyond hydrogen and helium) are formed in supernova explosions. The type of explosions depends on the mass of the stars involved. An absence of heavy elements indicates a lack of exploding supernova stars in a galaxy or area of a galaxy.

    When stars explode in supernovae, even heavier atoms are created. elements spew into space to infuse the gas that births the next generation of stars, so that each successive generation contains more and more heavy elements, known as metals.

    The term “metal” in astronomy, means any element other than hydrogen or helium. It is not the same as the chemical definition of “metal”!

    http://en.wikipedia.org/wiki/Metallicity

    As the OP points out, a lack of certain heavy elements indicates a lack of certain types of stars.

    • In reply to #1 by Alan4discussion:

      @OP- All supernovae are not created equal. When very massive stars blow up they form a mix of elements such as magnesium and calcium, whereas low-mass star explosions almost exclusively make iron.

      Just to make a simple point – All heavy elements (beyond hydrogen and helium) are formed in supernova…

      Actually, a number of elements heavier than helium can be formed inside stars as they age and others, even heavier, are formed if and when the star explodes as a supernova. The point is that these elements will remain locked inside the stars unless they do explode, and will not be available for the construction of new solar systems. The particular lack of iron in these stars suggests great age because the heavy elements they do contain came from very massive short-lived stars only.

      • In reply to #3 by Macropus:
        >

        Actually, a number of elements heavier than helium can be formed inside stars as they age and others, even heavier, are formed if and when the star explodes as a supernova. The point is that these elements will remain locked inside the stars unless they do explode, and will not be available for the construction of new solar systems.

        I agree. I should have made it clearer that I was talking about the heavy elements available for new star/planet formation after dispersal by supernova explosions. The point is well made, that the limited quantities of these heavy elements, are locked in old long lived stars in these ancient primordial galaxies.

    • In reply to #1 by Alan4discussion:
      >

      All heavy elements (beyond hydrogen and helium) are formed in supernova explosions. The type of explosions depends on the mass of the stars involved.

      On re-reading this, I have written the first comment rather poorly.

      The comment should say-; “All heavy elements (beyond hydrogen and helium) are formed in stars and in supernova explosions – being distributed back into space by supernova explosions, where they mix with hydrogen to form second and third generation stars and planetary systems. The type of reactions and any explosions depend on the mass of the stars involved.”

  2. The ancient dwarf galaxy might even have given birth to our Milky Way and surely our super massive black hole…might have had an effect on its small neighbours metallic elements ? other than that .. some of its stars could have been obliterated by passing or colliding galaxies ? I suppose the metallic elements are what keeps galaxies growing larger but the hydrogen only elements just keep them spinning or could galaxies even begin shrinking or contracting in size once metallic elements are used up…
    Its great how every new discovery leads to more questions being asked…

    • In reply to #2 by Light Wave:

      The ancient dwarf galaxy might even have given birth to our Milky Way and surely our super massive black hole…might have had an effect on its small neighbours metallic elements ?

      This is the wrong way round. It is the heavy galaxies with heavy elements which have stronger gravity and draw in lighter smaller, satellite galaxies.

      other than that .. some of its stars could have been obliterated by passing or colliding galaxies ?

      Stars don’t “get obliterated by passing galaxies”. Gravitational perturbations trigger more star formation in gas clouds in addition to existing stars. Colliding galaxies merge into larger galaxies, while black holes grow as they swallow stars, planets and smaller black holes.

      I suppose the metallic elements are what keeps galaxies growing larger but the hydrogen only elements just keep them spinning or could galaxies even begin shrinking or contracting in size once metallic elements are used up…

      In stars, it is hydrogen which gets used up. Heavy elements accumulate in galaxies over time as their older stars go super-nova and explode. A lack of heavy elements is the sign of a galaxy without many second or third generation stars, which have formed from heavy elements from earlier supernova explosions mixing with primordial hydrogen gas clouds and forming new stars. Spinning of galaxies, is just a gravitational effect of matter falling into orbits which do not collide with the central black hole.

      As far as habitable planets are concerned, only areas of galaxies with heavy elements can form rocky planets like Earth or Mars. Without these heavy elements, planets are just balls of gas.

      Its great how every new discovery leads to more questions being asked…

      It is the lack of second-generation stars containing heavy elements, which gives us cause to think this galaxy “May Be One of First Ever Formed”.

      I hope this helps to clarify some issues.

      • In reply to #4 by Alan4discussion:

        In reply to #2 by Light Wave:

        This is the wrong way round.

        Galactic archaeology is not my strong point – but i’m still fascinated anyway…..thanks for even bothering to clarify my muddy puddle of understanding

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