A SYMMETRICALLY PULSED JET OF GAS FROM AN INVISIBLE PROTOSTAR IN ORION

Young stars are thought to accumulate most of their mass through an ac cretion disk, which channels the gas and dust of a collapsing cloud on to the central protostellar object(1). The rotational and magnetic for ces in the star-disk system often produce high-velocity jets of outflo wing gas(2-6). These jets-an in principle be used to study the accreti on and ejection history of the system, which is hidden from direct vie w by the dust and dense gas of the parent cloud. But the structures of these jets are often too complex to determine which features arise at the source and which are the result of subsequent interactions with, the surrounding gas. Here we present infrared observations of a very y oung jet driven by an invisible protostar in the vicinity of the Horse head nebula in Orion. These observations reveal a sequence of geyser-l ike eruptions occurring at quasi-regular intervals and with near-perfe ct mirror symmetry either side of the source. This symmetry is strong evidence that such features must be associated with the formation of t he jet, probably related to recurrent or even chaotic instabilities in the accretion disk.