They called me mad at the academy, MAD I tell you...the villagers say that I am insane, but my monster will show them that I am really kind and benevolent.
Saturday, May 12, 2007
Precisely dating a star? not so fast
Centauri Dreams reports on the highly-precise (three significant figures) measure of the age of a star. Something doesn't quite add up in the method used to date the star, though. Elements heavier than Iron cannot be formed through the regular fusion mechanism of a star; it requires more energy for the fusion to take place than is released by the fusion, so the only place these elements can form is in a type II supernova. So, the elements Uranium, Thorium, Europium, Osmium, and Iridium cannot have formed within HE 1523-0901, and instead must have formed in a nearby precursor star and then been incorporated by HE 1523-0901 sometime after the precursor star went supernova. To then use the ratios of those elements as a measure of the age of the star, by treating HE 1523-0901 as if it was a lump of rock undergoing normal radioactive decay processes, is simply not valid - the ratios of those elements originally produced in the supernova is unknown, so their present-day ratios are not an indication of HE 1523-0901's age.
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2 comments:
Thank God this wasn't an article, somthing along the lines of Dancing with the Stars, which my mind kept looking for after having read the title.
I'm not at all good with the math involved in your explanations; I leave that to my daughter, and yet I find it facinating that some folks are able to hone their minds to such a degree as to make such explanations possible. Thank you.
Ed, here's your answer. This is from Anna Frebel, lead author on the paper in question -- I'm also posting it on Centauri Dreams, but thought you might like to see it here as well. I had sent her your comment and asked for a response:
"He is correct with the statement that all the neutron-capture elements
were indeed produced in a SN and not in HE 1523 itself. However, we
already know from the 'intrinsic' chemical composition of HE1523 that the
star is very old (but no age dating is possible that way). Furthermore,
the chemical pattern of neutron-capture elements in HE1523 follows the
pattern of the scaled solar r-process pattern. From that we know
that theses elements only came from just one SN. To achieve that HE 1523
much have formed from gas that was polluted with neutron-capture elements
in a previous-generation SN. So, to be precise, we are indeed age dating
the SN event that produced these elements. However, the formation
timescale of HE 1523 after the SN event is very short compared to the
stars age, hence the SN age equals the star's age. The ages I have derived
have an uncertainty of 1-2 billion years old which takes this time
difference into account.
And the initial production ratio's of my cosmic clocks are calculated
theoretically.
BTW: neutron-capture elements= Eu,Os, Ir, Th, U, etc
Hope this helps! Things always have to be a bit simplified in press
release to not confuse everybody :-)"
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