  Magnetic flux ropes (MFRs) rising buoyantly through the Sun's convection zone
are thought to be subject to viscous forces preventing them from rising
coherently. Numerous studies have suggested that MFRs require a minimum twist
in order to remain coherent during their rise. Furthermore, even MFRs that get
to the photosphere may be unable to successfully emerge into the corona unless
they are at least moderately twisted, since the magnetic pressure gradient
needs to overcome the weight of the photospheric plasma. To date, however, no
lower limit has been placed on the critical minimum twist required for an MFR
to rise coherently through the convection zone or emerge through the
photosphere. In this paper, we simulate an untwisted toroidal MFR which is able
to rise from the convection zone and emerge through the photosphere as an
active region that resembles those observed on the Sun. We show that untwisted
MFRs can remain coherent during their rise and then pile-up near the
photosphere, triggering the undular instability, allowing the MFR to emerge
through the photosphere. We propose that the toroidal geometry of our MFR is
critical for its coherent rise. Upon emerging, a pair of lobes rises into the
corona which interact and reconnect, resulting in a localized high speed jet.
The resulting photospheric magnetogram displays the characteristic
salt-and-pepper structure often seen in observations. Our major result is that
MFRs need not be twisted to rise coherently through the convection zone and
emerge through the photosphere.
