An extraordinary galactic jet ejected from a supermassive black hole boasts a corkscrew-like helical structure, new ground-based telescope views reveal.
The black hole lies at the center of an elliptical galaxy called Messier 87 (M87), which is located roughly 55 million light-years from Earth. The black hole — the first, and only, black hole ever photographed — is about 6.5 billion times more massive than the sun and shoots out a stream of material, also known as a galactic jet.
Using the National Science Foundation's Karl G. Jansky Very Large Array (VLA) in New Mexico, astronomers found that the jet is channeled by a corkscrew-shaped magnetic field that stretches nearly 3,300 light-years from M87's central black hole. This is the longest magnetic field yet detected in a galactic jet, according to a statement from the National Radio Astronomy Observatory, which operates the VLA.
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"By making high-quality VLA images at several different radio wavelengths of the galaxy Messier 87 (M87), we were able to reveal the 3-dimensional structure of the magnetic field in this jet for the first time," Alice Pasetto, lead author of the study and an astronomer at the National Autonomous University of Mexico, said in the statement. "The material in this jet traces a double helix, similar to the structure of DNA."
The researchers used observations from the VLA to trace the polarization, or alignment, of radio waves emitted from the jet's magnetic field structure, as well as the strength of the magnetic field across different parts of the jet, according to the statement.
"Helical magnetic fields are expected close to the black hole, and are thought to play a highly important role in channeling the material into a narrow jet," Jose M. Marti, co-author of the study and an astronomer at the University of Valencia in Spain, said in the statement. "But we didn't expect to find such a strong helical field extending so far outward."
In the recent VLA images of M87, the corkscrew-shaped magnetic field lines extend 3,300 light-years from the galaxy's central black hole. That magnetic field around the black hole propels the jet of energy and matter far out into space. In this case, the VLA observations show that the M87 jet extends about 8,000 light-years long.
The new observations suggest that instabilities in the flow of material within the jet may create regions of higher pressure. This, in turn, could compress the magnetic field lines, causing them to be more ordered at the extreme distances seen in the M87 observations, according to the statement.
What's more, the interaction between the magnetic field and the unstable flow of material in the galactic jet is believed to cause the double-helix structure seen in the recent observations of M87.
"M87 is relatively near to us and its jet is very powerful, making it an excellent target for study," Jose L. Gomez, co-author of the study and an astrophysicist at the Institute of Astrophysics of Andalusia in Spain, said in the statement. "The clues it gives us can help us understand this very important and ubiquitous phenomenon in the universe."
Their findings were published Dec. 7 in The Astrophysical Journal Letters.