A tale of three tails: A misaligned streamer and mysterious structures around [BHB2007]1

TL;DR

This study presents ALMA observations of [BHB2007]1 revealing complex streamer-like structures, including a gravitationally bound infalling streamer that influences disk evolution and planetary formation, challenging traditional isolated star formation models.

Contribution

The paper provides the first detailed analysis of multiple streamer-like structures around [BHB2007]1, highlighting a gravitationally bound infall streamer and suggesting environmental interactions influence star and planet formation.

Findings

Identification of a gravitationally bound infalling streamer.

Streamer could double the mass available for planet formation.

Streamer likely formed through gravitational capture, not from the natal core.

Abstract

Recent discoveries of streamer-like structures around protostellar sources challenge the traditional picture of isolated, axisymmetric star formation. Here, we present new ALMA observations of [BHB2007]1, a flat-spectrum source connected to at least three such elongated structures. Two of these features are symmetrically located to the north and south of the disk, with velocities aligned with the disk on their respective sides. However, their unbound kinematics and curved morphology make it difficult to determine their origin. Possible explanations include outflows, interactions with the nearby BHB2 system, and hyperbolic infall, but none fully account for all observed properties. In contrast, a newly identified collimated structure to the west shows clear evidence of gravitationally bound infall. Estimates of its mass, mass infall rate, and angular momentum suggest that this infalling streamer would roughly double the mass budget available to form planets and tilt the disk by a few tens of degrees. Furthermore, its misalignment with the midplane of the disk and the lack of diffuse envelope emission indicate that the streamer may have formed due to gravitational capture of cloud material unrelated to the source's natal core. Together, these findings support a more dynamic picture of star formation, one where environmental interactions continue to shape conditions for building planetary systems.