ABOUT THIS IMAGE:
[Left] In this NASA Hubble Space Telescope image of the central region of the galaxy NGC 3862, an extragalactic jet of material moving at nearly the speed of light can be seen at the three o’clock position. The jet of ejected plasma is powered by energy from a supermassive black hole at the center of the elliptical galaxy, which is located 260 million light-years away in the constellation of Leo.
[Right] A sequence of Hubble images of knots (outlined in red, green, and blue) shows them moving along the jet over a 20-year span of observing. Astronomers were surprised to discover that the central knot (green) caught up with and merged with the knot in front of it (blue). The new analysis suggests that shocks produced by collisions within the jet further accelerate particles that are confined to a narrowly focused beam of radiation. The “X” marks the location of the black hole.
Object Names: 3C 264, NGC 3862
Image Type: Astronomical/Annotated
Credit: NASA, ESA, and E. Meyer (STScI)
Paula Cleggett-Haleim Headquarters, Washington, D.C.
James Elliott Goddard Space Flight Center, Greenbelt, Md.
Ray Villard Space Telescope Science Institute, Baltimore, Md.
NASA’s Hubble Space Telescope has revealed an unusual and fascinating new optical jet in the nucleus of the elliptical galaxy NGC 3862.
“It appears that we are seeing a new class of phenomenon,” says Dr. Philippe Crane of the European Southern Observatory, who discovered the jet in images sent back by the European Space Agency’s (ESA) Faint Object Camera on board HST. “The jet-like feature was totally unexpected in this galaxy. This is typical of the kinds of discoveries that were expected from HST.” Crane and ESA’s Faint Object Camera Instrument Definition Team made the observations.
NGC 3862, also known as 3C264, is a bright radio source and x-ray source. It is the sixth brightest galaxy in a rich cluster of galaxies known as Abell 1367, located at a distance of about 260 million light-years away in the constellation Leo.
Previous observations of NGC 3862 taken in radio wavelengths have revealed a jet-like structure that extends for a very long distance.
“Since the jet is only 0.6 arc seconds long (equivalent to the apparent width of a dime located 2.5 miles away), it would have been very difficult to see from a ground-based observatory,” says Crane. “The jet also is prominent in ultraviolet light. Both of these characteristics are
especially well exploited by the Faint Object Camera (FOC).”
NGC 3862 was observed with the FOC in the high resolution (f/96) mode, with two filters, on Jan. 25, 1992, . One exposure, taken in yellow-green light, was expected to reveal, outside the nucleus, the distribution of the normal, old stellar population in the galaxy. The second exposure, taken in the near-ultraviolet light, was intended to reveal evidence for a young hot stellar population in the nucleus. To their surprise, the researchers found the optical jet.
Extra-galactic jets are not well understood. They appear to transport energy in a confined beam out from the active nucleus of the host galaxy. Presumably, super-massive black holes are the powerhouses behind jets.
Extra-galactic jets have been detected in radio wavelengths in many active galaxies, but only a few have been seen in optical light. Astronomers do not yet understand why some jets are seen in visible light and others are not. They also would like to understand theconnection between radio and optical emissions.
The NGC 3862 jet does not fit easily into the standard model of jets. The new jet is markedly different in several ways from the optical jet seen in M87 – a galaxy previously studied in detail by HST. The NGC 3862 jet is about 750 light-years long, compared to a length of 5,000 light-years for the M87 jet. The jet in M87 is brighter at redder wavelengths because it emits reddish synchrotron radiation produced by high-speed electrons spiraling in the magnetic field which confines the jet. The NGC 3862 jet, however, is much brighter in ultraviolet light, relative to visual light.
“Further observations will be needed to clarify the nature of the emission seen in this jet” says Crane. This new type of jet suggests that astronomers are seeing a new and unexpected phenomena in galactic nuclei.
The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency.