Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Recent Developments in Gravitational Microlensing   Twenty-one years after Bohdan's seminal paper launched the field of
gravitational microlensing, it has radically diversified from a method narrowly
focused on finding dark matter to a very general astronomical tool.
Microlensing has now detected 12 planets, including several that are
inaccessible by other search methods. It has resolved the surfaces of distant
stars, served as a magnifying glass to take spectra of extremely faint objects,
and revealed a number of surprising phenomena. I take a sweeping look at this
remarkable technique, giving equal weight to its successes and to the tensions
that are continuing to propel it forward.

8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex