CH Cygni was originally thought to be a semi-regular variable, with a 90- to 100-day period and an amplitude of about one magnitude. However, in 1976 a hot blue continuum appeared in the spectrum, together with emission lines of hydrogen, helium, calcium, and iron; at the same time, CH Cygni grew brighter than it had ever been seen before and showed rapid fluctuations, especially in ultraviolet light. This superposition of two distinct spectra – a hot blue continuum with emission lines on top of a late-type absorption spectrum –
In 1984, radio emission was detected in the CH Cygni system, further studies of which revealed a bipolar jet-like structure.
Close-up of a CH Cygni jet
The shape of the jet in CH Cyg shows striking parallels with jets seen in very different astrophysical contexts, such as young stars or supermassive black holes located at the centers of galaxies. Because of its proximity it may be used as a small-scale model to study jet formation and propagation in much more complex and distant systems.
In a biological setting, symbiosis is defined as the "living together of unlike organisms," and describes close and long-term interactions between different species. In this sense, the astrophysical usage is apt because white dwarfs and red giants are very different stars. A red giant is extremely large and bright, with a relatively low temperature, while a white dwarf is small and faint with a high temperature.
Symbiosis is usually beneficial or essential to the survival of at least one of the species in the system, for example bees and flowers, birds and rhinos and clownfish and anemones. In the astrophysical context of symbiotic systems, the survival of the hot disk around the white dwarf, where the jet originates, depends on the wind of the red giant. The power, mass, and the speed of the jet are closely related to the white dwarf environment including the disk. Once formed, the jet disrupts and shapes the extended envelope and environment of the red giant, as the latter evolves toward the end point of its life as a planetary nebula. However, in some cases, if the white dwarf gains too much mass from the red giant, it may end up being completely destroyed in a Type Ia supernova explosion.
A paper describing the new observations of CH Cyg was published in the February 20, 2010 issue of the Astrophysical Journal Letters and was led by Margarita Karovska from the Harvard-Smithsonian Center for Astrophysics (CfA). The coauthors are Terrance Gaetz from CfA, Christopher Carilli from the National Radio Astronomy Observatory, Warren Hack from Space Telescope Science Institute, and John Raymond and Nicholas Lee, both from CfA.
Note: The text and image for this section came from the Chandra Observatory website.
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