  Metal atoms and small clusters introduced into superfluid helium (He II)
concentrate there in quantized vortices to form (by further coagulation) the
thin nanowires. The nanowires' thickness and structure are well predicted by a
double-staged mechanism. On the first stage the coagulation of cold particles
in the vortex cores leads to melting of their fusion product, which acquires a
spherical shape due to surface tension. Then (second stage) when these
particles reach a certain size they do not possess sufficient energy to melt
and eventually coalesce into the nanowires. Nevertheless the assumption of
melting for such refractory metal as tungsten, especially in He II, which
possesses an extremely high thermal conductivity, induces natural skepticism.
That is why we decided to register directly the visible thermal emission
accompanying metals coagulation in He II. The brightness temperatures of this
radiation for the tungsten, molybdenum, and platinum coagulation were found to
be noticeably higher than even the metals' melting temperatures. The region of
He II that contained suspended metal particles expanded with the velocity of 50
m/s, being close to the Landau velocity, but coagulation took place even more
quickly, so that the whole process of nanowire growth is completed at distances
about 1.5 mm from the place of metal injection into He II. High rate of
coagulation of guest metal particles as well as huge local overheating are
associated with them concentrating in quantized vortex cores. The same process
should take place not only for metals but for any atoms, molecules and small
clusters embedded into He II.
