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11/07/2002
An Anemic Star
Last week, when I mentioned casting my first vote for Dwight
Eisenhower, I didn''t realize that this week marks the 50th
anniversary of that vote and of moving with my family to New
Jersey. If I hadn''t read the November/December American
Heritage, these personal milestones would have passed me by
unnoticed. I also forgot that November 1 marked the 50th
anniversary of a truly earthshaking event, the explosion of the
first hydrogen bomb on an island in the Pacific Ocean. That poor
little island was obliterated in the explosion.
While the atom bombs dropped on Japan were awesome in their
destructive effects, the hydrogen bomb was a thousand times
more powerful. The atom bomb utilized nuclear fission, the
splitting up of atoms, while the hydrogen bomb employed
nuclear fusion, the fusing of atoms. The fusing of hydrogen
atoms {actually, protons) to form helium fuels our sun and the
stars and leads us to our topic this week. I haven''t written about
stars for a while but regular readers will know that I can''t resist
space-related topics for long. Take the newspaper article by Rick
Callahan headlined "Astronomers discover a star of the ''Class of
13 Billion B.C.''" that I saw last week in our Star Ledger.
The news article was based on a report by Norbert Christlieb and
8 co-authors that appeared in the October 31 issue of Nature.
Christlieb, a 36-year old assistant professor at Hamburger
Sternwarte in Hamburg, Germany has a good sense of humor. A
picture on his Web site shows him with his feet propped up on a
desk, which has two computer monitors and an open notebook.
Yet the caption assures us that this is not a picture of him at
work, but of him on his last holiday on La Palma island. Another
picture shows him smiling broadly, holding an overhead
projector with the lamp section of the projector covering his
upper face like a mask. I found Christlieb to be a kindred soul.
He follows up giving his e-mail address with his wish that all
bulk e-mail senders end up in hell! (I just finished deleting,
without reading, 34 bulk e-mail messages I received today!)
But I digress. Let''s get back to "The class of 13 Billion B.C.", so
termed by George C. Preston, retired director of the Carnegie
Observatories in Pasadena, California. To appreciate the
significance of the work of Christlieb and his colleagues, we
have to go back to my favorite subject, the Big Bang. You may
recall that after the Bang there were no stars for quite a long
time. Finally, stars began to form. However, way back then
there was only hydrogen, some helium and a tad of lithium from
which to form these stars. In those early days, there weren''t any
metallic elements around.
So, how did the metallic elements like iron, for example, come
into being? They were formed in the interior of the stars where
all that fusion was going on, forming heavier and heavier
elements. When the bigger stars blew up as supernova, these
monumental explosions flung the iron and other heavy elements
out into the universe where new generations of stars were
formed. These new stars started out with some of that iron and
other heavy elements. As more generations of stars blew up and
new ones formed, the newer stars became richer and richer in
iron and the other heavy elements. Our sun is a relative
youngster as stars go, having formed only about 5 billion years
ago.
If this scenario is correct, one might hope to be able to look back
into time via a telescope and see light from that first generation
of stars formed 12 to 13 billion years ago. These earliest stars
should have a lot less iron in them than the stars of our present
day universe such as our sun. To actually see individual stars as
they were 12 billion years ago is asking a lot from our modern
telescopes, even as sophisticated as they are. What about the
possibility that there are nearby stars that formed in those earliest
of times and haven''t blown up or burned out? About 25 years
ago, astronomers did indeed find stars having 10,000 times less
iron than in our sun.
But some people are never satisfied. Christlieb and his ilk have
been trying to find stars of an even earlier vintage and now report
that they have found a star that is more than 12 billion years old.
This star has 200,000 times less iron than we find on the sun and
is thought to be a star formed from the debris of one of the very
first generation stars. What''s more, this star, quaintly named
HE0107-5240, is practically next door. It''s only 36,000 light
years away, near the center of our own Milky Way galaxy. The
hope is that such stars can help to reveal the composition of the
pristine gas resulting from the Big Bang.
How much iron is in our own star, the sun? Not having this
figure at my fingertips, I searched the Web and found on the
University of Tennessee, Knoxville site that the sun is 73% by
weight hydrogen and 25% helium, with iron weighing in at a
mere 0.14%. Other sources are roughly in agreement with these
figures. However, I was intrigued by a host of references on the
Web to "iron sun". When they weren''t related to a musical group
of some sort, these iron sun references concerned one Oliver
Manuel, a professor and retired department chairman at the
University of Missouri-Rolla.
Manuel claims that the interior of the sun is rich in iron and that
the lighter hydrogen makes its way to the surface, making it
seem that the sun is predominantly hydrogen. Typically,
abundance numbers such as I quoted above are obtained from the
spectra of the light emitted from the surface of a star. This "iron
sun" hypothesis is something Manuel has been espousing for 40
years and flies in the face of the conventional wisdom that the
sun is almost entirely hydrogen and helium.
Even more startling to me is Manuel''s assertion that our solar
system, including the sun, did not form from a swirling cloud of
nondescript gases and dust - the commonly accepted theory.
Rather, Manuel thinks the solar system arose from the explosion
of a single supernova, with the sun forming around the
supernova''s collapsed core. His postulate is that the outer planets
were formed from the outer envelopes of the debris of the
exploding star, while the earth and other inner planets were
formed from what was the inner regions of the iron-rich
exploding star. This, he says, would account for the fact that the
compositions of the planets are so different. The outer ones like
Jupiter and Neptune are gaseous planets while Earth, Venus and
Mars are rocky planets rich in iron and other heavy elements.
I get the impression that Manuel has had a hard time selling this
hypothesis. However, I did note that a NASA or Jet Propulsion
Lab Web site has a sketch of the sun that shows an iron core.
Getting back to Christlieb and his colleagues, if Manuel is
correct, it would seem that the newly found star would have even
less iron compared to that in the sun, making their find even
more impressive. Or does their star have an iron core too? If so,
would the total iron content be more or less than 200,000 times
less than the sun? Or is Manuel''s postulate totally wrong? If I
find out the answers I''ll let you know.
If you search "iron sun" on the Web, you can see a really neat
picture of the sun taken in the UV light emitted by ionized iron.
The picture, which in essence shows the distribution of iron on
the surface of the sun, was taken in 1996 from the SOHO
spacecraft. If you don''t like the (false) green color I found on the
University College London Web site, you can get it in blue,
judging from the title of another Web site. Whatever your color
choice, the picture shows that there''s an awful lot of whipping
around and swirling of that iron on the sun''s surface.
Allen F. Bortrum
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