Select Projects:

Formation and Evolution of Star Clusters and Associations

Using catalogs of young stellar objects from our previous studies combined with new astrometric measurements of their motions provided by the European Space Agency's Gaia mission, we obtained some of the first direct measurements of the expansion of newly formed star clusters and associations.

Our study demonstrated that most of the stellar groups in the star-forming regions we investigated are dynamically hot and in a state of expansion. Although many of the regions contain multiple groups of stars, and theory predicts that these subclusters may merge to form more massive clusters, we found no observational evidence of mergers.

Spatial distribution of stars in NGC 6530, with arrows to indicate the direction they are moving. The arrows have been color coded based on the direction they are pointing, so that bulk velocity gradients (e.g., expansion) will produce a visible color gradient.

Cluster Formation and Evolution – NGC 6231

The formation of star clusters is fundamental to astronomy because most stars form in groups of hundreds to thousands of stars, which later disperse. We studied a young, nearby cluster, NGC 6231, to learn how clusters evolve once their stars have formed.

Paper I - A deep new catalog is generated for the cluster based on X-ray observations (Figure 1) and VVV near-infrared photometry. We find evidence for a slight decrease in X-ray luminosity after several million years. We also find that a larger fraction of massive stars have pre-main-sequence binary companions.

Paper II - The cluster is remarkably well fit by an "isothermal sphere" surface density profile (Figure 2), despite its young age. Figure 3 compares the mass and size of NGC 6231 to groups of stars in other star-forming regions, including "typical" star-forming regions like those studied in the MYStIX project, and extreme, star-burst regions. We argue that NGC 6231 represents the end state of cluster assembly for a "typical" star-forming region.

Fig 1. Chandra X-ray Image of NGC 6231.

Fig 2. Comparison of surface density models (gray lines) to the observed distribution of stars in NGC 6231 (black lines).

Fig 3. Size versus mass for NGC 6231 (blue point), clusters and subclusters from MYStIX (black points), and rare, extreme starburst clusters (red points).

Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX)

(Co-PIs Feigelson & Townsley)

Adaptively smoothed maps of young stars in the different regions.

MYStIX is a study of 20 of the most massive star-forming regions within 3.6 kpc of the solar system, which has yielded a catalog of >30,000 young stars -- including some of the largest and cleanest samples of cluster members for many of these regions. Catalog papers and science results are listed at the MYStIX public website (

Science Papers:
The Spatial Structure of Young Stellar Clusters: Paper 1, Paper 2, Paper 3

AAS 2014 poster link:

NGC 2024 on APOD:

Preliminary results presented at the "Labyrinth of Star Formation" conference in Crete, Greece: Proceedings paper

The Young Stellar Cluster in W40


The W40 (= Westerhout 40) star-forming region (also known in the literature as the Aquila star-forming region, part of the Serpens molecular cloud) is one of the nearest massive star-forming regions in the Galaxy. Observations with the Chandra X-ray Observatory revealed a cluster of about 600 young stars.

Our inital study revealed a cluster that shows signs of being dynamically relaxed, including mass segregation, even though the it is likely to be less than 1 Myr old and to have ongoing star formation. With a new 80 ks Chandra observation we hope to double the number of stars detected and generate an improved model for star-formation in this region.

Star Formation in Nearby Clouds (SFiNCs)

(PI Getman)

Spitzer image of IC 5146.

The SFiNCs project is a follow-up to MYStIX concentrating on star-forming regions that are lower mass and nearer. I was PI of the Chandra proposal to obtain X-ray observations of the nebula IC 5146 (pictured) for the SFiNCs project. SFiNCs provides the best catalogs to date for these regions, available online from this url.