Breaking Cosmic Speed Limits: Powerful Astrophysical Jet Challenges Existing Theories
Recent studies of SS 433 have unveiled the mechanisms behind its gamma-ray emissions, revealing how particles are accelerated within its jets. This discovery challenges existing theories and provides a closer look at the processes driving relativistic jets, crucial for understanding cosmic phenomena.
How Gamma Rays Track the Velocity of the Galactic Microquasar SS 433’s Jets and Uncover Highly Efficient Particle Acceleration.
The microquasar SS 433 stands out as one of the most intriguing objects within our Milky Way. A pair of oppositely directed beams of plasma (“jets”) spirals away perpendicularly from the binary system's disk surface at just over a quarter of the speed of light.
The H.E.S.S. observatory in Namibia has now succeeded in detecting very high energy gamma rays from the jets of SS 433, and identifying the exact location within the jets of one of the galaxy’s most effective particle accelerators.
Through comparison of gamma-ray images at different energies, the H.E.S.S. collaboration was able to estimate the speed of the jet far from its launch site for the first time, constraining the mechanism that is accelerating the particles so efficiently.
Arthur C. Clarke’s Unique Wonder: SS 433
The science fiction author Arthur C. Clarke selected his own seven wonders of the world in a BBC television series in 1997. The only astronomical object he included was SS 433. It had attracted attention already in the late 1970s due to its X-ray emission and was later discovered to be at the center of a gas nebula that is dubbed the manatee nebula due to its unique shape resembling these aquatic mammals.
The Mystery of SS 433’s Jets
SS 433 is a binary star system in which a black hole, with a mass approximately ten times that of the Sun, and a star, with a similar mass but occupying a much larger volume, orbit each other with a period of 13 days. The intense gravitational field of the black hole rips material from the surface of the star, which accumulates in a hot gas disk that feeds the black hole.
As matter falls in toward the black hole, two collimated jets of charged particles (plasma) are launched, perpendicular to the plane of the disk, at a quarter of the speed of light.
The jets of SS433 can be detected in the radio to x-ray ranges out to a distance of less than one light year either side of the central binary star, before they become too dim to be seen. Yet surprisingly, at around 75 light-years distance from their launch site, the jets are seen to abruptly reappear as bright X-ray sources. The reasons for this reappearance have long been poorly understood.
Groundbreaking Gamma Ray Detection
Until recently, no gamma ray emission has ever been detected from a microquasar. But this changed in 2018, when the High Altitude Water Cherenkov Gamma-ray Observatory (HAWC), for the first time, succeeded in detecting very-high-energy gamma rays from the jets of SS 433. This means that somewhere in the jets, particles are accelerated to extreme energies.
Despite decades of research, it is still unclear how or where particles are accelerated within astrophysical jets.
