Cygnus OB2 is the nearest massive young stellar association to our Sun.
In this new composite image, the Chandra data (purple) shows the diffuse X-ray emission and young stars in Cygnus OB2, and infrared data from NASA’s now-retired Spitzer Space Telescope (red, green, blue, and cyan) reveals young stars and the cooler dust and gas throughout the region. Image credit: NASA / CXC / SAO / Drake et al. / JPL-Caltech / Spitzer / N. Wolk.
At a distance of about 1,400 parsecs (4,600 light-years), Cygnus OB2 is the closest massive young association to the Sun.
It contains hundreds of massive stars as well as thousands of lower-mass stars.
Dr. Mario Giuseppe Guarcello from the National Institute for Astrophysics, Dr. Juan Facundo Albacete-Colombo from the University of Rio Negro and colleagues used NASA’s Chandra X-ray Observatory to observe different regions of Cygnus OB2.
The deep observations mapped out the diffuse X-ray glow in between the stars, and they also provided an inventory of the young stars in the cluster.
This inventory was combined with others using optical and infrared data to create the best census of young stars in the association.
“In these crowded stellar environments, copious amounts of high-energy radiation produced by stars and planets are present,” the astronomers said.
“Together, X-rays and intense ultraviolet light can have a devastating impact on planetary disks and systems in the process of forming.”
Protoplanetary disks around stars naturally fade away over time. Some of the disk falls onto the star and some is heated up by X-ray and ultraviolet radiation from the star and evaporates in a wind.
The latter process, known as photoevaporation, usually takes between 5 and 10 million years with average-sized stars before the disk disappears.
If massive stars, which produce the most X-ray and ultraviolet radiation, are nearby, this process can be accelerated.
The researchers found clear evidence that protoplanetary disks around stars indeed disappear much faster when they are close to massive stars producing a lot of high-energy radiation.
The disks also disappear more quickly in regions where the stars are more closely packed together.
For regions of Cygnus OB2 with less high-energy radiation and lower numbers of stars, the fraction of young stars with disks is about 40%.
For regions with more high-energy radiation and higher numbers of stars, the fraction is about 18%.
The strongest effect — meaning the worst place to be for a would-be planetary system — is within about 1.6 light-years of the most massive stars in the cluster.
In a separate study, the same team examined the properties of the diffuse X-ray emission in Cygnus OB2.
They found that the higher-energy diffuse emission comes from areas where winds of gas blowing away from massive stars have collided with each other.
“This causes the gas to become hotter and produce X-rays,” they said.
“The less energetic emission probably comes from gas in the cluster colliding with gas surrounding the cluster.”
_____
M.G. Guarcello et al. 2024. Photoevaporation and Close Encounters: How the Environment around Cygnus OB2 Affects the Evolution of Protoplanetary Disks. ApJS 269, 13; doi: 10.3847/1538-4365/acdd67
J.F. Albacete-Colombo et al. 2024. Diffuse X-Ray Emission in the Cygnus OB2 Association. ApJS 269, 14; doi: 10.3847/1538-4365/acdd65
