Cygnus X is a star forming region in the constellation Cygnus in the night sky. It looks rather pretty in visible light, as shown at the beginning of the video below. But in radio, infrared and gamma ray wavelengths, Cygnus X really comes to life.
Recent Fermi Large Area Telescope (LAT) observations have shown that cavities created by massive stars within star forming clouds in the region are filled with gamma rays, created when the clouds are struck by cosmic rays.
Cygnus X is located 4,500 light years away from us. It has enough matter to make two million stars like our Sun, but contains stars that are much more massive than that.
Within Cygnus X are star clusters mainly made up of the hottest and brightest types of star — O and B type stars. These clusters, known as OB associations, are just five million years old — young, in stellar terms. O and B type stars are the most massive, which is why they’re so rare compared to other types of star. They “sculpt” the gas clouds in which they reside, emitting radiation and massive stellar winds that create cavities that surround the stars. In doing this the stars clear the area surrounding them of gas, making it much harder for more stars to form close by. They effectively climb up the ladder of star formation then kick it back down once they’ve got to the top.
Cygnus X was discovered in the 1950s as a source of radio waves. Now, Fermi LAT observations show a huge 160 light year across “cocoon” of cosmic rays exists in the region. The Fermi team said in a paper published in Science on November 25th that the cosmic rays “flood” the cavities carved out by massive stars in young star clusters.
Cosmic rays are beams of subatomic particles, usually protons, that travel through space at close to the speed of light — much like particles in a particle accelerator like the Large Hadron Collider.
When cosmic rays travel through space they get pushed about by magnetic fields which alter their path, making it difficult to see where the cosmic ray originated. When they meet the gas the lives between stars, they produce gamma rays. Gamma rays, unlike cosmic rays, are able to travel through whatever is in their way, arriving at Earth having followed a straight line path for their whole journey — so we can see where they originated.
The source of cosmic rays is a long standing problem in astrophysics. By tracing gamma rays, Fermi’s LAT can play a part in helping astronomers work out exactly where cosmic rays come from.
The newly discovered “cocoons” of cosmic rays are held together by magnetic fields created by the outflows from massive stars in the region. Shockwaves from the stars knot up the magnetic field so the cosmic rays become trapped.
Gamma Cygni, the remnant of a dying star — or supernova — exists within the Cygnus X region, making it a candidate for the cosmic ray source. But multiple shockwaves created by massive stars in the OB association is also considered as a possible source by the Fermi team.
This paper has shown that the life of a cosmic ray could be a lot more eventful than astronomers previously thought.
Ackermann, M., & et al (2011). A Cocoon of Freshly Accelerated Cosmic Rays Detected by Fermi in the Cygnus Superbubble Science, 334 (6059), 1103-1107 DOI: 10.1126/science.1210311
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