Stellar jets are huge outbursts of plasma from a young star, planetary nebula or black hole that can be trillions of kilometres long and expand at speeds anywhere from hundreds of kilometres a second to something approaching the speed of light.
Jets like these are the result of a ring of dust and gas (called an accretion disc) being pulled into a dense object like a protostar or black hole and subsequently being fired out from its two poles in opposite directions. However, what exactly happens between the material being sucked from the disc into its host object and then being propelled into interstellar space is a matter of debate.
Another mystery is the longevity of the jets. Previously, it was thought that they are constantly emitted, but observations of scattered jet material suggests that they actually fire periodically like relativistic bullets, spreading debris into the interstellar medium as the star or black hole rotates.