Core accretion models of massive star formation require the existence of stable massive starless cores , but robust observational examples of such objects have proven elusive .
We report subarcsecond-resolution SMA 1.3 mm , 1.1 mm , and 0.88 mm and VLA 1.3 cm observations of an excellent massive starless core candidate , G11.92 - 0.61–MM2 , initially identified in the course of studies of GLIMPSE Extended Green Objects ( EGOs ) .
Separated by \sim 7 \farcs 2 from the nearby MM1 protostellar hot core , MM2 is a strong , compact dust continuum source ( submillimeter spectral index \alpha = 2.6 \pm 0.1 ) , but is devoid of star formation indicators .
In contrast to MM1 , MM2 has no masers , no centimeter continuum , and no ( sub ) millimeter wavelength line emission in \sim 24 GHz of bandwidth observed with the SMA , including N _ { 2 } H ^ { + } ( 3-2 ) , HCO ^ { + } ( 3-2 ) , and HCN ( 3-2 ) .
Additionally , there is no evidence for an outflow driven by MM2 .
The ( sub ) millimeter spectral energy distribution ( SED ) of MM2 is best fit with a dust temperature of \sim 17-19 K and luminosity of \sim 5-7 L _ { \odot } .
The combined physical properties of MM2 , as inferred from its dust continuum emission , are extreme : M \gtrsim 30 M _ { \odot } within a radius < 1000 AU , N _ { H _ { 2 } } > 10 ^ { 25 } cm ^ { -2 } and n _ { H _ { 2 } } > 10 ^ { 9 } cm ^ { -3 } .
Comparison of the molecular abundance limits derived from our SMA observations with gas-grain chemical models indicates that extremely dense ( n ( H ) > > 10 ^ { 8 } cm ^ { -3 } ) , cold ( < 20 K ) conditions are required to explain the lack of observed ( sub ) millimeter line emission , consistent with the dust continuum results .
Our data suggest that G11.92 - 0.61–MM2 is the best candidate for a bonafide massive prestellar core found to date , and a promising target for future , higher-sensitivity observations .