Astronomer ‘dives’
into galactic black hole
Prof might
have this one
‘in the bag’
By KATHLEEN MONJE
Of the Emerald
The possibility of “black holes”
in space has fascinated as
trophysicists and science-fiction
writers for decades.
The idea of an invisible gravita
tional field so dense that not only
matter but light disappear inside it
is both intriguing and almost in
comprehensible.
For the past three years, Uni
versity astronomer James Kemp
has been investigating a possible
black hole in the star system Cyg
nus X-1.
"This is the only case where
people think they have one in the
bag," Kemp said. “Cygnus X-l is
the only known binary (two-star
system) where the secondary star
is highly compact (or collapsed)
and at the same time has suffi
cient mass to be a black hole.”
A black hole is the third stage of
a star that has collapsed in upon
itself, astronomers say.
The first is the white dwarf, and
the second is the neutron star,
which has compressed enough
that its protons and electrons have
merged to become neutrons.
Black holes and neutron stars are
detectable only through X-ray
telescopes.
"If you look at Cygnus X-l in an
ordinary telescope, you will see
only a single star,” Kemp exp
lained. But the black star can be
detected visually by its influence
— “anything that comes within its
sphere disappears.”
Kemp's research team has
concentrated on comparing the
visible and X-ray light variations
from Cygnus X-l. He presented
the results of their work at an
American Astronomical Society
meeting Wednesday in Austin,
Texas.
“My work has shown that the
star system is more complex and
interesting than previously
thought,” Kemp said. One result is
a different way of measuring the
secondary star’s mass.
“The black hole is only half as
large as previously thought. It is
only three miles in diameter, with
the density of five solar masses,"
Kemp told his colleagues at the
meeting.
His research also suggests a
more controversial development:
the possibility of not one, but two,
unseen star masses orbitina the
visible Cygnus X-l.
Studies of Cygnus X-l have es
tablished a definite invisible mass
exerting a gravitational pull, which
causes well-identified light varia
tions every 5.6 days, on the visible
star some 7,000 light years from
Earth.
However, Kemp, and University
students working with him, found
additional faint light variations oc
curring in 78-day cycles, which
they think may be caused by a
third star with an eccentric orbit
somewhat similar to a comet s.
This third star, with a
mass less than our sun’s, causes
the light variations when it comes
close to Cygnus X-l and is heated
by the contact.
Further research over the next
two years could prove that the
second star is not a black hole,
Kemp said.
Photo by Steven Scher
James Kemp
Instead, the third star could be a
neutron star and the source of the
X-rays, with the secondary star
simply an ordinary one,” he said.
“In any case, it’s an extraordinary
system, because it’s the second
strongest X-ray source in the sky.”
Nobody has been able to make
a close connection between the
flux in X-ray emmissions from the
unseen star and the light varia
tions of the visible star, Kemp
said.
“It is as if the X-rays come from
a place very far removed from the
star we see in the telescope,” he
said.
I
“Astronomers have been put
ting black stars in the nuclei of
galaxies and in clusters of stars
without any evidence for them,”
Kemp said.
“It’s the job of observational as
tronomers like me to find out if
they really exist."
Neutron stars were predicted in
the 1930’s, he said, but the first
definite case wasn’t found until
1970.
“The idea is to get a black hole
we can play with, and verify all the
properties the theorists have
talked about,” he said. “Or, we
might prove they don’t exist."
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