The BATSE time history of gamma-ray emission from the transient
source GRO J1655-40 as compared to the radio lightcurve.
Optical studies showed that its orbital period was 2.6 days; 8-12 hours
is more typical. However, the real surprise was in the radio. GRO J1655-40
was found to be ejecting matter in highly collimated streams in a direction
nearly perpendicular to the plane of its binary orbit. Astronomers call
such streams of matter, "jets", in analogy to the stream of water
emitted from the nozzle of a high-pressure water hose. Jets had been seen
before, and are in fact quite common, in extremely distant, energetic objects
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known as "quasars". However, in our own galaxy, there are
only a few examples of jet-producing sources. What made GRO J1655-40 all
the more interesting was that time-lapsed sequences of observations revealed
that the jet- ejection velocities approached the speed of light; 92% of
the speed of light to be precise! Einstein's theory of relativity dictates
that no material object move with a velocity that exceeds the speed of
light, so GRO J1655-40 appeared to |
be hurling large quantities of material into space at 92% of the "cosmic
speed limit". Actually not quite: scientists studying quasars had
noted in the 1970's that a combination of projection effects and relativity
can produce the illusion of motion at, or even exceeding the speed of light,
but it still remains a hard and fast truth that physical matter never really
exceeds the speed of light. |
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To gamma-ray astronomers, or for that matter to scientists in general,
the prospect of finding the unexpected is often the most exciting endeavor!
For GRO J1655-40, the team of gamma-ray astronomers using CGRO, radio astronomers
using the Very Large Array (VLA - an array of radio telescopes mounted
in an 22-mile long "Y" shaped configuration on the desert of
New Mexico), and astronomers working in the visible domain using telescopes
in the Chilean Andes were not disappointed! What they discovered was that
GRO J1655- 40 did in fact contain a black hole. |