Q24 - Science journalist: Brown dwarfs

[dayme11]

I am really confused with this game. (A) seemed like the right answer to me because the statement said that if it has less mass than the sun it does not have lithium.

Can you please explain to me why (A) is not the answer and also what would be the best way to approach these types of questions. Whenever I get a question with a science topic I seem to get it wrong. What can I do to improve this problem that I have.

[bbirdwell]

Science questions are no different than any other question on the test. At times, actually, their structure can be easier to understand, even if the individual words cannot, because they tend to rely on studies and statistics. Just treat them as you would any other problem and don't allow yourself to develop a "complex" about them!

This is a tough question! And it's not because it's science -- it's because of the way it's written. It's not so much an exercise in understanding science as it is an exercise in de-constructing a difficult argument and navigating double-negatives in the answer choices.

Here's what we know:
1. Brown dwarfs = celestial objects with more mass than planets and less mass than stars

2. Brown dwarfs = ID'd by their mass and whether or not they have Lithium

3. Stars at least as massive as Sun have Lithium

4. Stars with less mass than Sun don't have Lithium

The last sentence is key! Don't get distracted by the nuclear furnace chit-chat. The point is that Brown Dwarfs' Lithium "cannot be consumed."
Therefore,
5. Brown Dwarfs have Lithium

(A) is incorrect because it says "any celestial object." The statements we have regarding the Sun are limited to stars.

(B) similar problem. The discussion of "nuclear furnaces" is about stars, not all celestial objects.

(C) is awkward because of the negatives, but translated correctly says: "celestial object with no Lithium --> not a Brown dwarf." Yes! This must be true! Brown dwarfs have Lithium!

(D) Again, mass of the Sun is compared only to other stars and Brown dwarfs. For all we know, there are other celestial objects out there that meet this criteria. Therefore, we cannot prove this choice.

(E) Similar issue. The only thing we know for sure about celestial objects less massive than Brown dwarfs is that some of them are planets. The presence or absence of Lithium is unknown to us.

[lisahollchang]

Thanks for the reply! I was also confused by this question. I thought brown dwarfs could have lithium because of statement #2, and didn't think through the implications of the last sentence.

[esnanees]

Can ans choice C be translated as: Celestial object that has lithium in its atmosphere is a brown dwarf?

If so, wouldn't that be so broad?........so doesn't mean any celestial object with lithium is brown dwarf?

Can someone please help with clarifying this?
thanks

[austindyoung]

Can ans choice C be translated as: Celestial object that has lithium in its atmosphere is a brown dwarf?

If so, wouldn't that be so broad?........so doesn't mean any celestial object with lithium is brown dwarf?

Can someone please help with clarifying this?
thanks

I think you got a little confused with how to take out the negatives is (C)

We would actually have this:

ANY celestial object that has NO lithium in its atmosphere is NOT a brown dwarf star

HTH

[hychu3]

Hi,

I chose (C) without much confidence only because I was able to eliminate all other answer choices.

(C) takes some questionable logical gaps in my opinion. Here is how it goes:

Nowhere does the stimulus logically commit itself to the existence of lithium in the atmospheres of brown dwarfs. It only suggests that possibility indirectly by saying brown dwarfs do not have fully functional nuclear furnaces.

We do not know if there are factors other than nuclear furnaces that can contribute to the lack of lithium in the atmosphere. Moreover, even if there is no such other factor, we are still not given enough information to properly infer that brown dwarfs necessarily have lithium in the atmosphere, just as we cannot infer the same about the planets, for example.

This is a "most strongly supported" question, and as such the correct answer choice probably is not as perfect as those in "must be true" questions. The correct answer choice is the one that has the least logical gap. This can be potentially problematic, because what constitues a "smaller" logical gap than others can be rather arbitrary.

[ohthatpatrick]

I agree with most of what you said, but you didn't mention the other piece of supporting evidence we have:

"its lithium cannot be consumed".

If I tell you:
"A brown dwarf's lithium cannot be consumed"
then that seems to directly imply that brown dwarfs DO have at least some lithium, and it also implies that nothing ever extinguishes that lithium (nuclear furnaces OR anything else).

The entire logic of the sentence implies that nuclear furnaces actually ARE the only thing that would consume lithium, because it says "BD's do not have X, and so they cannot do Y."

That implies that only X could do Y.

If we got a claim such as:
"A brown dwarf's nuclear furnace would never be able to consume all lithium in a brown dwarf's atmosphere"
then you would have a claim more vulnerable to the objections you were making:

- Does the atmosphere necessarily have lithium to begin with?
- Could something else possible consume the lithium?

But the final sentence is pretty rock solid support for (C).

[obobob]

Here's what we know:
1. Brown dwarfs = celestial objects with more mass than planets and less mass than stars

2. Brown dwarfs = ID'd by their mass and whether or not they have Lithium

3. Stars at least as massive as Sun have Lithium

4. Stars with less mass than Sun don't have Lithium

The last sentence is key! Don't get distracted by the nuclear furnace chit-chat. The point is that Brown Dwarfs' Lithium "cannot be consumed."
Therefore,
5. Brown Dwarfs have Lithium

Just a quick question:
Brown dwarfs, planets, and stars are all celestial objects, but are “stars” in the third and fourth premises as quoted above (and also in the actual text of the stimulus) just plainly indicating celestial objects?

If so, why would LSAC distinguish brown dwarfs, planets, and stars in the first sentence? I was kind of confused since it seemed like we cannot infer much about brown dwarfs out of the third and fourth premises.

[Laura Damone]

Hey, obobob! I see you posted in this forum but the post appears to be blank. If you've got a question, please repost and we'll answer it for you!