The resolved jet of 3C 273 at 150 MHz
  Since its discovery in 1963, 3C273 has become one of the most widely studied
quasars with investigations spanning the electromagnetic spectrum. While much
has been discovered about this historically notable source, its low-frequency
emission is far less well understood. Observations in the MHz regime have
traditionally lacked the resolution required to explore small-scale structures
that are key to understanding the processes that result in the observed
emission. In this paper we use the first sub-arcsecond images of 3C273 at MHz
frequencies to investigate the morphology of the compact jet structures and the
processes that result in the observed spectrum. Using the full complement of
LOFAR's international stations, we produce $0.31 \times 0.21$ arcsec images of
3C273 at 150 MHz to determine the jet's kinetic power, place constraints on the
bulk speed and inclination angle of the jets, and look for evidence of the
elusive counter-jet at 150 MHz. Using ancillary data at GHz frequencies, we fit
free-free absorption (FFA) and synchrotron self-absorption (SSA) models to
determine their validity in explaining the observed spectra. The images
presented display for the first time that robust, high-fidelity imaging of
low-declination complex sources is now possible with the LOFAR international
baselines. We show that the main small-scale structures of 3C273 match those
seen at higher frequencies and that absorption is present in the observed
emission. We determine the kinetic power of the jet to be in the range of $3.5
\times 10^{43}$ - $1.5 \times 10^{44}$ erg s$^{-1}$ which agrees with estimates
made using higher frequency observations. We derive lower limits for the bulk
speed and Lorentz factor of $\beta \gtrsim 0.55$ and $\Gamma \geq 1.2$
respectively. The counter-jet remains undetected at $150$ MHz, placing a limit
on the peak brightness of $S_\mathrm{cj\_150} < 40$ mJy beam$^{-1}$.
