# The fastest components in stellar jets

## TL;DR

This paper investigates the inner, fastest components of stellar jets in young stars, emphasizing their importance in angular momentum loss and star formation, and highlights the need for high-energy observations and modeling.

## Contribution

It presents new insights into the nature of the inner jet components in stellar outflows and underscores the importance of high-energy observations for understanding star formation.

## Key findings

- Inner jet components are fast and carry little mass.
- High-energy observations are crucial for studying inner jets.
- Understanding inner jets is key to star formation theories.

## Abstract

Young stars accrete mass from a circumstellar disk, but at the same time disk and star eject outflows and jets. These outflows have an onion-like structure where the innermost and fastest layers are surrounded by increasingly lower velocity components. The outer layers are probably photo-evaporative and magnetocentrifugally launched disk winds, but the nature of the inner winds is still uncertain. Since the fastest components carry only a small fraction of the mass, they are best observed at high-energies (X-ray and UV) as the slower, more massive components do not reach plasma temperatures sufficient for relevant X-ray or UV emission. Outflows are the most likely way in which a star or its disk can shed angular momentum and allow accretion to proceed; thus we cannot understand the accretion and the rotation rate of young stars if we cannot solve the origin of the inner jet components. Stellar jets share characteristics with their counterparts in more massive astrophysical objects, such as stellar mass black holes and AGN, with the added benefit that young stars are found at much closer distances and thus scales not accessible in other types of objects can be resolved. To understand the origin and impact of the inner jets, sub-arcsecond imaging and spectroscopy in the UV and X-rays is required, together with theory and modelling to interpret existing and future observations.