  The Pipe Nebula, a large nearby molecular cloud lacks obvious signposts of
star formation in all but one of more than 130 dust extinction cores that have
been identified within it. In order to quantitatively determine the current
level of star formation activity in the Pipe Nebula, we analyzed 13 square
degrees of sensitive mid-infrared maps of the entire cloud, obtained with the
Multiband Imaging Photometer for Spitzer (MIPS) at wavelengths of 24 micron and
70 micron to search for candidate Young Stellar Objects (YSOs) in the
high-extinction regions. We argue that our search is complete for class I and
typical class II YSOs with luminosities of Lbol~0.2 Lo and greater. We find
only 18 candidate YSOs in the high-extinction regions of the entire Pipe cloud.
Twelve of these sources are previously known members of a small cluster
associated with Barnard 59, the largest and most massive dense core in the
cloud. With only six candidate class I and class II YSOs detected towards
extinction cores outside of this cluster, our findings emphatically confirm the
notion of an extremely low level of star formation activity in the Pipe Nebula.
The resulting star formation efficiency for the entire cloud mass is only ~0.06
%.
