Credit X-ray: NASA/CXC/SAO/J. Drake et al, IR: NASA/JPL-Caltech/Spitzer; Image Processing: NASA/CXC/SAO/N. Wolk
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A team of astronomers used NASA’s Chandra X-ray Observatory, in combination with ultraviolet, optical, and infrared data, to show where some of the most treacherous places in a star cluster may be, where planets’ chances to form are diminished.
The target of the observations was Cygnus OB2, which is the nearest
large cluster of stars to our Sun — at a distance of about 4,600 light-years.
The cluster contains hundreds of massive stars as well as thousands of
lower-mass stars. The team used long Chandra observations pointing at
different regions of Cygnus OB2, and the resulting set of images were
then stitched together into one large image.
The deep Chandra 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 cluster.
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.
In these crowded stellar environments, copious amounts of high-energy
radiation produced by stars and planets are present. Together, X-rays
and intense ultraviolet light can have a devastating impact on planetary
disks and systems in the process of forming.
Planet-forming 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 using this data found clear evidence that
planet-forming 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.
A separate study by the same team examined the properties of the
diffuse X-ray emission in the cluster. 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. The less energetic emission probably
comes from gas in the cluster colliding with gas surrounding the
cluster.
Two separate papers describing the Chandra data of Cygnus OB2 are
available. The paper about the planetary danger zones, led by Mario
Giuseppe Guarcello (National Institute for Astrophysics in Palermo,
Italy), appeared in the November 2023 issue of the Astrophysical Journal
Supplement Series, and is available here.
The paper about the diffuse emission, led by Juan Facundo
Albacete-Colombo (University of Rio Negro in Argentina) was published in
the same issue of Astrophysical Journal Supplement, and is available here.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages
the Chandra program. The Smithsonian Astrophysical Observatory's Chandra
X-ray Center controls science operations from Cambridge, Massachusetts,
and flight operations from Burlington, Massachusetts.
JPL managed the Spitzer Space Telescope mission for NASA’s Science
Mission Directorate in Washington until the mission was retired in
January 2020. Science operations were conducted at the Spitzer Science
Center at Caltech. Spacecraft operations were based at Lockheed Martin
Space in Littleton, Colorado. Data are archived at the Infrared Science
Archive operated by IPAC at Caltech. Caltech manages JPL for NASA.
Visual Description:
The center of the square image is dominated by purple haze. This haze represents diffuse X-ray emissions, and young stars, detected by the Chandra X-ray observatory. Surrounding the purple haze is a mottled, streaky, brick orange cloud. Another cloud resembling a tendril of grey smoke stretches from our lower left to the center of the image. These clouds represent relatively cool dust and gas observed by the Spitzer Space Telescope.
Although the interwoven clouds cover most of the image, the thousands of stars within the cluster shine through. The lower-mass stars present as tiny specks of light. The massive stars gleam, some with long refraction spikes.
Fast Facts for Cygnus OB2:
Scale: Image is about 1.5 arcmin (120 light-years) across.
Category: Normal Stars & Star Clusters
Coordinates (J2000): RA 20h 33m 12s | Dec +41° 19´ 00"
Constellation: Cygnus
Observation Dates: 40 pointings between January 2004 and March 2010
Observation Time: 331 hours 30 minutes (13 days 19 hours 30 minutes)
Obs. ID: 4501, 4511, 7426, 10939-10974, 12099
Instrument: ACIS
References: Guarcell, M.G. et al, 2023, ApJS, 269, 13; Albacete-Colombo, J.F. et al, 2023, ApJS, 269, 14.
Color Code: X-ray: purple; Infrared (IRAC): red, green, blue; Infrared (MIPS): cyan;
Distance Estimate: About 4,600 light-years
