Q:

The function of 만 in 바라만보다 and difference from 바라보다

After coming by the expression 바라만 보다, I spent more than two hours trying to find something on it, and just before posting that very question here, I got the bright idea of putting the whole term 바라만보다 into Naver. I was told that 바라만보다 is a conjugation of 바라다보다.
I tried looking further from there, but the results were only in Korean and unfortunately not comprehensible to me at this point (see below). I got the feeling that I really should have stopped there, but after spending the time and writing and scrapping an entire question on it here, I kind of want the rest of the picture.
My main thoughts and questions are:

What is the function (and possibly origin) of 만 in 바라만보다? It is certainly joining the two, but are there any other nuances to that? Are there any other words/expressions that this appears in?
Is 바라다보다/바라만보다 sort of archaic/poetic?
Is it any different from 바라보다, except from the archaic/poetic feel? Would it be usable in speech? (Naver claims they are synonyms)

A shorter answer to each of these would suffice, but not that I would refuse a comprehensive one.

The sources I found:

Question on korean.go.kr
Question on hinative.com

A:

Although jick gave a great answer, I would like to add some details in case you meet a word simliar to this later on.
We can breakdown "바라만 보다" into 3 parts:

바라 + 만 + 보다

Q1 : '만' is a postposition that can add various kinds of meanings, and is able to come :

after a noun

after a verb

and sometimes even in between a verb when the word is in (main verb + auxilary verb) form

and according to the Standard Korean Dictionary, postposition '만' means :

showing limitation by restricting ('only' in English)
ex) 나는 매일 사과 하나만 먹는다. (I only eat an apple everyday.)

emphasizing the noun/verb that came before it (similar to 'has to' in English)
ex) 그녀는 건강을 위해 뛰어야만 한다. (She has to run for her health.)

showing the minimun quantitiy of expectation (similar to 'at least' in English)
ex) 다섯 개의 오디션 중 하나만 붙어라. ((I) hope (I) pass at least one audition out of five.)

comparing the noun/verb that comes before it with another (used with "하다" or "못하다", similar to "just like" / "no where near" in English)
ex) 그의 새 차가 코끼리만 하다. (His new car is just like an elephant.)

showing the condition for something (similar to "everytime")
ex) 나는 뛰기만 하면 다친다. (I get hurt everytime I run.)

'만' appears in so many different parts in Korean.
In our case '바라만 보다', '만' comes in between a verb, and is showing limitation by restricting. So it means "only staring at it. (no other actions taken)"
Q2 : So no, '바라만 보다' is not archaic/poetic. It is used in daily conversations, and is actually used very often!
(but it is also true that '바라만 보다' is used often in lyrics/poems/classic novels because it has that "sad, heartbroken" feel to it.)
Q3 : Using answers from Q1 and Q2, we can now say that '바라만 보다' is interpreted as (only + '바라보다'), and we can use it in everyday speech.

