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Cygnus X1 – The First
Cygnus X1
In the early Seventies scientists found an intensive X-Ray source in the
Cygnus Constellation. They believe that this X-Ray source is a black hole.
Cygnus X-1 is an X-ray binary in the
constellation Cygnus, the swan, that was
one of the first X-ray sources discovered
when it was detected in 1962. It is called
Cygnus X-1 because it was the first X-ray
source discovered in the constellation
Cygnus. The visible object HDE226868 is a
9th magnitude blue supergiant star whose
radial velocity curve shows an orbital period
of a little less than a week. The fact that the
object is a strong X-ray emitter and that the
optical and X-ray emission varies on very
short time scales (as short as one onethousandth of a second) suggest that the
companion might be a black hole.
Cygnus X1
Cygnus X-1 is one of the most likely candidates as
being a black hole. Cygnus X-1 is about 14,000
light years away from earth. So this means that
what we are seeing, is many, many, years old. It is
a very inconsistent source for X-ray emissions. The
emissions of X-rays for Cygnus X-1 flicker in
hundredth of a second bursts. It is also been
proven that Cygnus X-1 is smaller than the Earth.
Strangely enough, Cygnus X-1 has a companion
star called HDE 226868. HDE 226868 is a
supergiant with a temperature around 31,000 K.
After extremely close observations of HDE 226868,
it appears that its spectral lines (light given off at a
certain frequency by an atom or molecule) shift
back and forth it a rotation of about 5.6 days. Other
images show that its mass would be about 30
times as much as the sun for its size. This would
mean that Cygnus X-1 would have the mass of
about 7 solar masses for its gravitational pull to
exhibit the shifts in the spectral lines on HDE
226868. Because 7 solar masses is too big to be a
white dwarf or neutron star, it must be a black
hole.
HDE 226868 and
Cygnus X-1 X-ray
emissions
Cygnus X1
Cygnus X-1 is believed to be a black hole binary, with a 20-35 solar mass
black hole and a supergiant, orbiting around with a period of 5.6 days,
as companion. The mass of the unseen companion, significantly larger
then 5 solar masses suggests that it is a black hole. Focused wind
accretion from a primary star being extremely close to filling the Roche
lobe drives the powerful source of the X-ray radiation. Cygnus X-1 is
one of the brightest X-ray sources in the sky.
Cygnus X1
Subrahmanyan Chandrasekhar first determined the upper limit to the
mass of a white dwarf as 1.4 solar masses. This value, called the
Chandrasekhar mass limit, is still used today. Later, J.R. Oppenheimer
and G.M. Volkoff determined the upper mass of a neutron star. It is
called the Oppenheimer-Volkoff mass, and has been recalculated many
times since. Because we are dealing with degenerate neutron gas,
which we can only make educated guesses about the exact properties
of, we cannot truly determine precisely what this limit is. It is usually
said to be about 2 to 3 solar masses, and generally stays well below 4 or
5.
Cygnus X1
Is there really a black hole in
Cygnus?
Scientists don't know if this is
really a black hole. It could be a
small star, too faint to see in
optical wavelengths, or possibly a
planet sized hunk of rock. But the
Object is too small for a star. A
better explanation is that the object
is a neutron star or a white dwarf.
Neutron Stars usually have very
regular and distinct pulses.
Cygnus X-1's emmissions,
however, show no regularity or
periodicity. They seem to have no
repeating patterns, and vary on
short and long timescales equally.
Cygnus X1
There is evidence that says that Cygnus X-1 is not a black hole. It could be that
HDE 226868 has a low mass for its size, resulting in Cygnus X-1 having a lower
mass it self. If this were the case, Cygnus X-1 may only be the mass of 3 solar
masses and would be likely be a neutron star. A neutron star is a more stable body
of the remains from a super nova explosion of a large star compared to a black
hole.
Since both neutron stars and black holes give off X-rays, this is a convincing
argument on how Cygnus X-1 might not be a black hole. It has also been found in
recent years, that both black holes and neutron stars give off gamma rays. The
new images collected using gamma rays provides a much more clear
representation of black holes and neutron stars. Gamma ray images can also can
be artificially colored to a more precise scale, making them easier to understand.
The discovery still doesn't answer the question rather Cygnus X-1 is a black hole
or neutron star, but still should help aid the discovery of other new black holes or
neutron stars