Jets from Young Stars in Cygnus-X

How do you spot very young, newly formed stars? One giveaway is the presence of jets and outflows that interact with the stars’ environments. In a new study, scientists have now discovered an unprecedented number of these outflows in a nearby star-forming region of our galaxy.

Young Stars Hard at Work

The birth and evolution of young stars is a dynamic, energetic process. As new stars form, material falls inward from the accretion disks surrounding young stellar objects, or YSOs. This material can power collimated streams of gas and dust that flow out along the stars’ rotation axes, plowing through the surrounding material. Where the outflows collide with the outside environment, shocks form that can be spotted in near-infrared hydrogen emission.

Though we’ve learned a lot about these outflows, there remain a number of open questions. What factors govern their properties, such as their lengths, luminosities, and orientations? What is the origin of the emission features we see within the jets, known as knots? What roles do the driving sources and the environments play in the behavior and appearance of the jets?

To answer these questions, we need to build a large, unbiased statistical sample of YSOs from across the galactic plane. Now, a large infrared survey — known as the UKIRT Widefield Infrared Survey for H₂ (UWISH2) — is working toward that goal.

Jackpot in Cygnus-X

In a recent publication, Sally Makin and Dirk Froebrich (University of Kent, UK), present results from UWISH2’s latest release: a survey segment targeting a 42-square-degree region in the galactic plane known as the Cygnus-X star-forming region.

The team’s search for shock-excited emission in Cygnus-X yielded spectacular results. They found a treasure trove of outflows — a remarkable 572 in total, representing a huge increase over the 107 known previously.

Makin and Froebrich then measured properties of the outflows themselves — such as length, orientation, and flux — as well as properties of the sources that appear to drive them.

Pinning Down Properties

Of the 572 outflows, the authors found that 27% are one-sided jets and 46% are bipolar. The bipolar outflows are typically ~1.5 light-years in total length, and they are frequently asymmetric, with the shorter jet lobe averaging only 70% the length of the longer one. The flux from the two sides of bipolar jets is also often asymmetric: typically one side is brighter by about 50%.

Exploring the knots of bright emission within the outflows, the authors found that they are typically closely spaced, suggesting that the material generating them is ejected every 900–1,400 years. This rapid production — faster than what has been found in YSO outflows in other regions — rules out some models of how these knots are produced.

Based on the fraction of UWISH2 data analyzed so far, the authors estimate that the entire UWISH2 survey will uncover a total of ~2,000 jets and outflows from YSOs. This large, unbiased new sample is finally allowing astronomers to build out the statistics of YSO outflows to better understand them.

Citation

S. V. Makin and D. Froebrich 2018 ApJS 234 8. doi:10.3847/1538-4365/aa8862