NASA's Chandra Contributes to Black Hole Birth Announcement

NASA's Chandra Contributes to Black Hole Birth Announcement












New details about the birth of a famous black hole that took place millions of years ago have been uncovered, thanks to a team of scientists who used data from NASA's Chandra X-ray Observatory as well as from radio, optical and other X-ray telescopes.

Over three decades ago, Stephen Hawking placed -- and eventually lost -- a bet against the existence of a black hole in Cygnus X-1.
Today, astronomers are confident the Cygnus X-1 system contains a black
hole, and with these latest studies they have remarkably precise values
of its mass, spin, and distance from Earth. With these key pieces of
information, the history of the black hole has been reconstructed. "This
new information gives us strong clues about how the black hole was
born, what it weighed and how fast it was spinning," said author Mark
Reid of the Harvard-Smithsonian Center for Astrophysics (CfA) in
Cambridge, Mass. "This is exciting because not much is known about the
birth of black holes."

Reid led one of three papers -- all appearing in the November 10th
issue of The Astrophysical Journal -- describing these new results on
Cygnus X-1. The other papers were led by Jerome Orosz from San Diego
State University and Lijun Gou, also from CfA.

Cygnus X-1 is a so-called stellar-mass black hole, a class of black
holes that comes from the collapse of a massive star. The black hole is
in close orbit with a massive, blue companion star.

Using X-ray data from Chandra, the Rossi X-ray Timing Explorer, and
the Advanced Satellite for Cosmology and Astrophysics, a team of
scientists was able to determine the spin of Cygnus X-1 with
unprecedented accuracy, showing that the black hole is spinning at very
close to its maximum rate. Its event horizon -- the point of no return
for material falling towards a black hole -- is spinning around more
than 800 times a second.

An independent study that compared the evolutionary history of the
companion star with theoretical models indicates that the black hole was
born some 6 million years ago. In this relatively short time (in
astronomical terms), the black hole could not have pulled in enough gas
to ramp up its spin very much. The implication is that Cygnus X-1 was
likely born spinning very quickly.

Using optical observations of the companion star and its motion
around its unseen companion, the team made the most precise
determination ever for the mass of Cygnus X-1, of 14.8 times the mass of
the Sun. It was likely to have been almost this massive at birth,
because of lack of time for it to grow appreciably.

"We now know that Cygnus X-1 is one of the most massive stellar black
holes in the Galaxy," said Orosz. "And, it's spinning as fast as any
black hole we've ever seen."

Knowledge of the mass, spin and charge gives a complete description
of a black hole, according to the so-called "No Hair" theorem. This
theory postulates that all other information aside from these parameters
is lost for eternity behind the event horizon. The charge for an
astronomical black hole is expected to be almost zero, so only the mass
and spin are needed.

"It is amazing to me that we have a complete description of this
asteroid-sized object that is thousands of light years away," said Gou.
"This means astronomers have a more complete understanding of this black
hole than any other in our Galaxy."

The team also announced that they have made the most accurate
distance estimate yet of Cygnus X-1 using the National Radio
Observatory's Very Long Baseline Array (VLBA). The new distance is about
6,070 light years from Earth. This accurate distance was a crucial
ingredient for making the precise mass and spin determinations.

The radio observations also measured the motion of Cygnus X-1 through space, and this was combined with its measured velocity to give the three-dimensional velocity and position of the black hole.

This work showed that Cygnus X-1 is moving very slowly with respect
to the Milky Way, implying it did not receive a large "kick" at birth.
This supports an earlier conjecture that Cygnus X-1 was not born in a
supernova, but instead may have resulted from the dark collapse of a
progenitor star without an explosion. The progenitor of Cygnus X-1 was
likely an extremely massive star, which initially had a mass greater
than about 100 times the sun before losing it in a vigorous stellar
wind.

In 1974, soon after Cygnus X-1 became a good candidate for a black
hole, Stephen Hawking placed a bet with fellow astrophysicist Kip
Thorne, a professor of theoretical physics at the California Institute
of Technology, that Cygnus X-1 did not contain a black hole. This was
treated as an insurance policy by Hawking, who had done a lot of work on
black holes and general relativity.

By 1990, however, much more work on Cygnus X-1 had strengthened the
evidence for it being a black hole. With the help of family, nurses, and
friends, Hawking broke into Thorne's office, found the framed bet, and
conceded.

"For forty years, Cygnus X-1 has been the iconic example of a black
hole. However, despite Hawking's concession, I have never been
completely convinced that it really does contain a black hole -- until
now," said Thorne. "The data and modeling described in these three
papers at last provide a completely definitive description of this
binary system."

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the
Chandra program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory controls Chandra's science and
flight operations from Cambridge, Mass.

More information is available at:http://www.nasa.gov/chandra