2025ApJ...985..120C

We report that the formation of the twin-bubble system N65 and N65bis may be caused by the cloud-cloud collision (CCC) from the Bullet Nebula. The blueshifted ¹³CO gas component (N65a [47, 55] km s^–1) is associated with the twin-bubble system, while the redshifted ¹³CO gas component (N65b [55, 62] km s^–1) is linked to the Bullet Nebula. The distinct signatures of CCC, such as the bridge feature, the U-shaped cavity, and the complementary distribution with displacement, are found between N65a and N65b. The collision timescale is estimated to be 1.15-2.0 Myr, which is consistent with the dynamical ages of the two H II regions in N65a (0.73 Myr for N65bis and 1.19 Myr for N65, respectively), indicating their CCC-related origin. A total of 354 young stellar objects (YSOs) are found, which are clustered into eight minimum spanning tree groups. The distribution of M1 (at the post-frontal edge) and M2, M3, M4 (at the pre-frontal edge) suggests that the CCC triggers star formation along the collision path of $b=0\mathop{.}\limits^{^\circ }35$, with younger YSOs present at the pre-frontal edge. Therefore, the bipolar morphology of the twin-bubble system can be interpreted by the collision of N65a and N65b along $b=0\mathop{.}\limits^{^\circ }35$ about 2 Myr ago.