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NASA's RXTE Helps Pinpoint Launch of 'Bullets' in a Black Hole's Jet

Jan. 10, 2012

Trent J. Perrotto
Headquarters, Washington

RELEASE: 12-009


WASHINGTON -- Using observations from NASA's Rossi X-ray Timing 
Explorer (RXTE) satellite and the National Science Foundation's (NSF) 
Very Long Baseline Array (VLBA) radio telescope, an international 
team of astronomers has identified the moment when a black hole in 
our galaxy launched superfast knots of gas into space. 

Racing outward at about one-quarter the speed of light, these 
"bullets" of ionized gas are thought to arise from a region located 
just outside the black hole's event horizon, the point beyond which 
nothing can escape. 

"Like a referee at a sports game, we essentially rewound the footage 
on the bullets' progress, pinpointing when they were launched," said 
Gregory Sivakoff of the University of Alberta in Canada. He presented 
the findings today at the American Astronomical Society meeting in 
Austin, Texas. "With the unique capabilities of RXTE and the VLBA, we 
can associate their ejection with changes that likely signaled the 
start of the process." 

The research centered on the mid-2009 outburst of a binary system 
known as H1743-322, located about 28,000 light-years away toward the 
constellation Scorpius. Discovered by NASA's HEAO-1 satellite in 
1977, the system is composed of a normal star and a black hole of 
modest but unknown masses. Their orbit around each other is measured 
in days, which puts them so close together that the black hole pulls 
a continuous stream of matter from its stellar companion. The flowing 
gas forms a flattened accretion disk millions of miles across, 
several times wider than our sun, centered on the black hole. As 
matter swirls inward, it is compressed and heated to tens of millions 
of degrees, so hot that it emits X-rays.

Some of the infalling matter becomes re-directed out of the accretion 
disk as dual, oppositely directed jets. Most of the time, the jets 
consist of a steady flow of particles. Occasionally, though, they 
morph into more powerful outflows that hurl massive gas blobs at 
significant fractions of the speed of light. 

In early June 2009, H1743-322 underwent this transition as astronomers 
watched with RXTE, the VLBA, the Very Large Array near Socorro, N.M., 
and the Australia Telescope Compact Array (ATCA) near Narrabri in New 
South Wales. The observatories captured changes in the system's X-ray 
and radio emissions as the transformation occurred.

>From May 28 to June 2, the system's X-ray and radio emissions were 
fairly steady, although RXTE data show that cyclic X-ray variations, 
known as quasi-periodic oscillations or QPOs, gradually increased in 
frequency over the same period. On June 4, ATCA measurements showed 
that the radio emission had faded significantly.

Astronomers interpret QPOs as signals produced by the interaction of 
clumps of ionized gas in the accretion disk near the black hole. When 
RXTE next looked at the system on June 5, the QPOs were gone. 

The same day, the radio emission increased. An extremely detailed VLBA 
image revealed a bright, radio-emitting bullet of gas moving outward 
from the system in the direction of one of the jets. On June 6, a 
second blob, moving away in the opposite direction, was seen. 

Until now, astronomers had associated the onset of the radio outburst 
with the bullet ejection event. However, based on the VLBA data, the 
team calculated that the bullets were launched on June 3, about two 
days before the main radio flare. A paper on the findings will be 
published in the Monthly Notices of the Royal Astronomical Society.

"This research provides new clues about the conditions needed to 
initiate a jet and can guide our thinking about how it happens," said 
Chris Done, an astrophysicist at the University of Durham, England, 
who was not involved in the study.

A super-sized version of the same phenomenon occurs at the center of 
an active galaxy, where a black hole weighing millions to billions of 
times our sun's mass can drive outflows extending millions of 

"Black hole jets in binary star systems act as fast-forwarded versions 
of their galactic-scale cousins, giving us insights into how they 
work and how their enormous energy output can influence the growth of 
galaxies and clusters of galaxies," said lead researcher James 
Miller-Jones at the International Center for Radio Astronomy Research 
at Curtin University in Perth, Australia. 

The Rossi X-ray Timing Explorer, which operated from Dec. 1995 to Jan. 
2012, was managed by NASA's Goddard Space Flight Center in Greenbelt, 
Md. The VLBA, the world's largest and highest-resolution astronomical 
instrument, is controlled from the National Radio Astronomy 
Observatory's Domenici Science Operations Center.

For images and animations related to this story, please visit:



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