APOD: J102815: A Star That Should Not Exist (2011 Sep 07)

[bystander]

... Furthermore, even the elusive never-seen first stars in the universe, so-called Population III stars, are predicted to have a large mass and a small but set amount of heavy elements. ...

Ummm... from following the links it seems that our sun would be a generation III star and these elusive never-seen first stars should be Population I?

Population I is is not a term for first generation stars but for the youngest generation. They were named in order of discovery so, since our Sun was obviously in the first group to be discovered, that group was designated Population I.

See Wikipedia: Metallicity: Populations III, II, and I

[RJN]

Why does this star have so few heavy elements?

After some thought, I have decided to stick with the word "few" and to try to weather the storm. One reason is that substituting the word "less" just doesn't sound right to me. Putting in "less" would have the reader demanding to know "less than what?" and feel frustrated when that question is not answered right in the next sentence. Now surely the word "few" is also comparative, but I think less so -- in my mind it does not bring up the phrase "fewer than what" as strongly. Sometimes when I write (OK,"type in words" might be more accurate), I try to create a flow of thoughts in the readers mind. Here the word "less" does not create as good a flow as "few", in my opinion. Were the words exactly equal in meaning and flow and the only problem being one of grammatical correctness, I would make the change. I apologize if this disappoints and convinces many that I am not only illiterate, but willfully so.

- RJN

[bystander]

Why does this star have so few heavy elements?

... the stars that created most of the heavy elements around us today, are seen to have some, although less, elements heavier than H and He ...

... low-mass Milky Way star SDSS J102915+172927, among others, appears to have less metals than ever predicted for any stars ...

I think the objection was to your use of less instead of fewer, not few instead of less.

In any case, I support your choice of comparatives, and join you in being willfully illiterate.

[Chris Peterson]

How about this "theory": there is a vast amount of nearly-impossible-to-detect MOLECULAR hydrogen in interstellar and inter-galactic space, which allows this type of star to form AND accounts for the (non existent) 'dark matter'. :)

Molecular hydrogen makes up most of the interstellar medium; the problem with this star is that it contains only hydrogen and helium. The modern ISM is "contaminated" with heavier elements, so why don't these show up in an apparently new star?

Molecular hydrogen is, of course, ordinary baryonic matter, which means it isn't a candidate for dark matter. The dynamics of dark matter makes it clear that it doesn't interact with ordinary matter, so it must be something quite different.

[drollere]

this star is very faint ... i cannot find it in the millennium star atlas, not even in stellarium, so it must be below v.mag. 15. my question is how it was identified in the first place, given the time required for even a large aperture scope to collect enough light to do the detailed spectroscopy. assuming that similar data were collected for the millions of stars at or below that magnitude, seriously clever computation was necessary to sort this spectrum out of the huge pile. i'd certainly like to know more about that.

re the syntactic cat fight: i don't mind stress tests of english grammar, because our grammar is wonderfully flexible and expressive; but i think the writer could benefit from less reliance on the digressive comma, and more effort at arranging ideas into a linear flow.

[NoelC]

One has to wonder if there are any natural processes that throughout the eons might have resulted in everything heavier than hydrogen being drawn away (e.g., by gravity), then finally a star formed from the purified gas.

We simply can't presume to know all the processes that can take (or have taken) place out in the wild, wonderful universe.

-Noel

[flash]

On LESS vs FEWER (my view):

The important distinction is whether the variables being compared are DISCRETE or CONTINUOUS. When comparing the NUMBER of elements present "FEWER" is the correct word. On the other hand when comparing the relative abundance of heavy or light elements, then LESS is correct word. Similarly, when comparing energy content of two items, it is correct to say FEWER calories. not LESS calories. But it is also correct to say LESS energy, but certainly not FEWER energy. On the plus side, MORE works for both discrete and continuous variables. Hope this helps!

[Chris Peterson]

this star is very faint ... i cannot find it in the millennium star atlas, not even in stellarium, so it must be below v.mag. 15.

At around mag 17, this star would generally be considered pretty bright. It is orders of magnitude brighter than the SDSS detection limit.

my question is how it was identified in the first place, given the time required for even a large aperture scope to collect enough light to do the detailed spectroscopy.

It was detected by the SDSS, which amongst other data provides information that can be used to infer metallicity. As the paper notes, the researchers identified nearly 3000 stars in the SDSS data that were candidates for close examination, which they then narrowed down by visibility and other factors, performing spectroscopy on six before settling on this particular star.

[Wolf kotenberg]

Has this particular " soup " been duplicated in a lab ? Is this more like water and oil of more like smoke and air ?

[Chris Peterson]

Has this particular " soup " been duplicated in a lab ? Is this more like water and oil of more like smoke and air ?

What "soup" are you referring to?

[islader2]

@ owlice==Your contributions to this "blog" are too valuable to have you involved, crabbily, with some of our less-astronomy minded posters. Your nom-de-plume is bound to arouse other solons to enter into an unworthy discussion of semantics and grammar. I liked it better when you directed newcomers to the rules for posting. Thanx.

[islader2]

@ NEUFER. There has been enough nitpicking on today's Asterisk to last forever. But, humbly, I must comment on the photo of General Petraeus and the "fruit salad" on his tunic==since I have worn some of the same "salad." Some is medal bars==some is awards. I would hate think that I was medaled for being in combat as a foot-soldier, or for being a paratrooper. Those are awards that we wear proudly==not service ribbons. Thanx.

[drollere]

At around mag 17, this star would generally be considered pretty bright. It is orders of magnitude brighter than the SDSS detection limit.

thanks, chris. as a visual astronomer i guess i work in a shallower pond. what then is a "faint" star -- mag. 20? how many stars are available to scrutiny in the SDSS survey? i see cites to only about 250,000 under two project headings.

As the paper notes, the researchers identified nearly 3000 stars ...

yes, but there is a lot of handwaving about how it all works ... fiber optics, CCDs, computers, poof! 3000 stars. does SDSS have a paper on the actual processes?

[Boomer12k]

25% Helium....so it talks in a high, squeaky voice????

:-------======== *

[Chris Peterson]

thanks, chris. as a visual astronomer i guess i work in a shallower pond. what then is a "faint" star -- mag. 20? how many stars are available to scrutiny in the SDSS survey? i see cites to only about 250,000 under two project headings.

Mag 19 is faint for SDSS spectroscopy, mag 23 is faint for SDSS imaging. Data release 7, which was used by these researchers, has about a half million stellar spectra. With the data release 8 this year, that number is now much higher.

yes, but there is a lot of handwaving about how it all works ... fiber optics, CCDs, computers, poof! 3000 stars. does SDSS have a paper on the actual processes?

There's a lot of good information on the SDSS site... I wouldn't call it "handwaving". Spectroscopic data is collected with a fairly standard survey tool, consisting of custom drilled plates matching stellar fields, which apertures connected via fiber optic to a spectrograph. The instrument is described here.

[Wolf kotenberg]

The ' soup " i mentioned earlier was just a moniker I used to describe the mixture. I could have just as easily described it as a mixture of 25% helium plus 75% hydrogen but do you have any idea how long it takes me to rtype that ?

[Chris Peterson]

The ' soup " i mentioned earlier was just a moniker I used to describe the mixture. I could have just as easily described it as a mixture of 25% helium plus 75% hydrogen but do you have any idea how long it takes me to rtype that ?

Nobody has created sustained fusion at all in a laboratory, so there is no "experimental" model for a star, except via numerical simulation.

[mst66186]

... Furthermore, even the elusive never-seen first stars in the universe, so-called Population III stars, are predicted to have a large mass and a small but set amount of heavy elements. ...

Ummm... from following the links it seems that our sun would be a generation III star and these elusive never-seen first stars should be Population I?

Population I is is not a term for first generation stars but for the youngest generation. They were named in order of discovery so, since our Sun was obviously in the first group to be discovered, that group was designated Population I.

OK. Thanks for the info. I got confused because of the text "Our own Sun is thought to be a third generation star, with many second-generation stars seen in globular clusters" on the page behind the link 'Population III'. I agree it's important for one to 'say what you mean and mean what you say'!

[starman]

Lithium is actually the signature of a very young star, since once the core fusion process kicks off, Li is rapidly destroyed. So, find Li in a star's spectrum and you've got a YSO.
Incidentally, as an honours graduate in English/Linguistics, I think all this faffing about with Fewer/Less is an irrelevancy. "Fewer" is, on the basis of usage, rapidly becoming redundant (at least here in the UK). The meaning is absolutely clear - "not so much as", "a smaller quantity than", etc. It's just pedantry in the same class as 'you should never split infinitives' or 'never end a sentence with a preposition'.

[khearn]

I'm coming into this discussion very late, and I apologize for being off-topic and discussing the star, not the language usage.

It occurs to me that this star is somewhat similar to Earth's moon. Both are lacking in expected heavy elements. Might they have had similar origins? Could the collision (or near collision) of two stars have caused enough material from the outer layers of the stars to be expelled, so that a new star could form from it? This material from the outer layers of the stars would likely me almost all hydrogen and helium, since the heavier elements would be concentrated near the cores of the stars. Two very large stars passing close to each other would probably draw off tidal tails, similar to two galaxies passing close to each other. If the stars are big enough, could the material draw off could be sufficient to form a new, small, and metal-deficient star?

I know such a collision is incredibly unlikely, but the universe is a big place, so even very unlikely things are likely to have happened.