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Astronomers Uncover a Baby Galaxy in a Grown-Up Universe
Scientists using NASA's Hubble Space Telescope have measured the age of what may be the youngest galaxy ever seen in the universe. By cosmological standards it is a mere toddler seemingly out of place among the grown-up galaxies around it. Called I Zwicky 18, it may be as young as 500 million years old.
Everything I need to know I learned through Googling.
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You have been ToSeeked by Kullat Nunu
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Aww, who's my baby galaxy? Yes you are, yes you are!
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The article notes that, "Further evidence for the youth of I Zwicky 18 is the fact that its interstellar gas is "nearly pristine," Thuan said, and composed mostly of hydrogen and helium, the primary two light elements created in the Big Bang, during the first three minutes of the universe's existence. The dwarf galaxy includes only a sprinkling of the other heavier elements such as carbon, nitrogen, or oxygen that are created later as stars develop. The near absence of such heavy elements suggests that much of the primordial gas in the dwarf galaxy has not managed to form stars that subsequently manufacture heavy elements."Originally Posted by ToSeek
Imagine that. More observational support for a big bang scenario.
Everyone is entitled to his own opinion, but not his own facts.
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Who would have thought? :wink:
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That's not quite happenstance. I Zw 18 has been observed in great detail as an example of a metal-poor galaxy, since it was first noted spectroscopically (in the 1970s) as having unusually low oxygen and nitrogen abundances. Further searches, some quite intensive, have failed to turn up any galaxies with more-pristine gas, although some do come close (SBS 0335 and 1415-what's-their-names come to mind). I Zw 18 remains the benchmark for what stellar populations look like at low abundances, something like 2% of the solar value. And maybe less - analysis of the far-UV spectrum shows hints that even what we see in the ionized gas has been enriched by stars, and that the surrounding cooler gas is more like 1/500 of the solar value.The article notes that, "Further evidence for the youth of I Zwicky 18 is the fact that its interstellar gas is "nearly pristine," Thuan said, and composed mostly of hydrogen and helium, the primary two light elements created in the Big Bang, during the first three minutes of the universe's existence. The dwarf galaxy includes only a sprinkling of the other heavier elements such as carbon, nitrogen, or oxygen that are created later as stars develop. The near absence of such heavy elements suggests that much of the primordial gas in the dwarf galaxy has not managed to form stars that subsequently manufacture heavy elements."
At this metal level, the lives of massive stars change. They lose less mass to winds during their lifetimes (since stellar winds are mostly launched by radiation pressure which is most effective on heavy elements), and thus have more mass left when the blow up. Observationally, we can tell that the winds are weaker in I Zw 18 than in more metal-rich galaxies (nice big plot comparing spectra to be seen in http://www.arxiv.org/abs/astro-ph/0403499).
While cosmically just yesterday, the 500 Myr age is not what some folks had expected a few years ago - finding any evidence of star formnation before the curren 10 Myrs or so means that we really can't say this one has been caught in some sort of delayed formation. Even so, it does fit in an interesting way with results of redshift surveys that have led to the "downsizing" picture of galaxy formation. This means that the most massive galaxies formed their stars fastest, and finished first, while the least massive galaxies are still building up their stellar mass at a good clip. Statistically, at least...
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