NASA News: NASA's RXTE Detect 'Heartbeat' of Smallest Black Hole Candidate
WASHINGTON -- An international team of astronomers has identified acandidate for the smallest-known black hole using data from NASA's
Rossi X-ray Timing Explorer (RXTE). The evidence comes from a
specific type of X-ray pattern, nicknamed a "heartbeat" because of
its resemblance to an electrocardiogram. The pattern until now has
been recorded in only one other black hole system.
Named IGR J17091-3624 after the astronomical coordinates of its sky
position, the binary system combines a normal star with a black hole
that may weigh less than three times the sun's mass. That is near the
theoretical mass boundary where black holes become possible.
Gas from the normal star streams toward the black hole and forms a
disk around it. Friction within the disk heats the gas to millions of
degrees, which is hot enough to emit X-rays. Cyclical variations in
the intensity of the X-rays observed reflect processes taking place
within the gas disk. Scientists think that the most rapid changes
occur near the black hole's event horizon, the point beyond which
nothing, not even light, can escape.
Astronomers first became aware of the binary system during an outburst
in 2003. Archival data from various space missions show it becomes
active every few years. Its most recent outburst started in February
and is ongoing. The system is located in the direction of the
constellation Scorpius, but its distance is not well established. It
could be as close as 16,000 light-years or more than 65,000
light-years away.
The record-holder for wide-ranging X-ray variability is another black
hole binary system named GRS 1915+105. This system is unique in
displaying more than a dozen highly structured patterns, typically
lasting between seconds and hours.
"We think that most of these patterns represent cycles of accumulation
and ejection in an unstable disk, and we now see seven of them in IGR
J17091," said Tomaso Belloni at Brera Observatory in Merate, Italy.
"Identifying these signatures in a second black hole system is very exciting."
In GRS 1915, strong magnetic fields near the black hole's event
horizon eject some of the gas into dual, oppositely directed jets
that blast outward at about 98 percent the speed of light. The peak
of its heartbeat emission corresponds to the emergence of the jet.
Changes in the X-ray spectrum observed by RXTE during each beat reveal
that the innermost region of the disk emits enough radiation to push
back the gas, creating a strong outward wind that stops the inward
flow, briefly starving the black hole and shutting down the jet. This
corresponds to the faintest emission. Eventually, the inner disk gets
so bright and hot it essentially disintegrates and plunges toward the
black hole, re-establishing the jet and beginning the cycle anew.
This entire process happens in as little as 40 seconds.
While there is no direct evidence IGR J17091 possesses a particle jet,
its heartbeat signature suggests that similar processes are at work.
Researchers say that this system's heartbeat emission can be 20 times
fainter than GRS 1915 and can cycle some eight times faster, in as
little as five seconds.
Astronomers estimate that GRS 1915 is about 14 times the sun's mass,
placing it among the most-massive-known black holes that have formed
because of the collapse of a single star. The research team analyzed
six months of RXTE observations to compare the two systems,
concluding that IGR J17091 must possess a minuscule black hole.
"Just as the heart rate of a mouse is faster than an elephant's, the
heartbeat signals from these black holes scale according to their
masses," said Diego Altamirano, an astrophysicist at the University
of Amsterdam in The Netherlands and lead author of a paper describing
the findings in the Nov. 4 issue of The Astrophysical Journal Letters.
The researchers say this analysis is just the start of a larger
program to compare both of these black holes in detail using data
from RXTE, NASA's Swift satellite and the European XMM-Newton
observatory.
"Until this study, GRS 1915 was essentially a one-off, and there's
only so much we can understand from a single example," said Tod
Strohmayer, the project scientist for RXTE at NASA's Goddard Space
Flight Center in Greenbelt, Md. "Now, with a second system exhibiting
similar types of variability, we really can begin to test how well we
understand what happens at the brink of a black hole."
Launched in late 1995, RXTE is second only to Hubble as the longest
serving of NASA's operating astrophysics missions. RXTE provides a
unique observing window into the extreme environments of neutron
stars and black holes.
For videos associated with the RXTE finding, visit:
http://www.nasa.gov/topics/
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NASA Center Signs Commercial Agreement With Sierra Nevada
WASHINGTON-- NASA's Marshall Space Flight Center in Huntsville, Ala.,is entering into a space act agreement with Sierra Nevada Corp. Space
Systems of Louisville, Colo., to provide key wind tunnel testing of a
new spacecraft designed to transport crew and cargo to and from the
International Space Station.
Marshall will perform wind tunnel tests for Sierra Nevada's Dream
Chaser orbital crew vehicle, a spacecraft that looks like a small
space shuttle. The tests will simulate speeds ranging from Mach .2,
or 152 mph at sea level, to Mach 5, or 3,811 mph at sea level, to
provide Sierra Nevada with aerodynamic data about how the vehicle
reacts at varying speeds and atmospheric conditions. Marshall will
provide engineering support and data processing throughout the test
series. The agreement could lead to joint development, testing and
operations of advanced space systems -- including innovative design
and fabrication techniques.
"Helping our commercial partners be successful is a top priority, and
we are pleased to be working with Sierra Nevada on Dream Chaser,"
said Teresa Vanhooser, manager of the Flight Programs and
Partnerships Office at Marshall. "Our experienced workforce and
unique wind tunnel offers our partners a proven, quick, and
affordable way to test their Dream Chaser vehicle, and will aid in
the development of the capability to transport astronauts to the
International Space Station."
Marshall's 14-square-foot wind tunnel is capable of conducting tests
at subsonic, transonic and supersonic wind speeds. Transonic speeds
are close to Mach 1, the speed of sound, or 760 mph at sea level, and
the facility can achieve wind speeds as great as Mach 5.
"We are extremely pleased to be adding the Marshall Space Flight
Center to our Dream Chaser Orbital spacecraft team, which now
includes seven NASA centers. Marshall has been at the forefront of
many significant aerospace programs, and we are fortunate to have
their terrific people and valuable technical capabilities assisting
us in the development of our vehicle. Our partnership will enable us
to reach low-Earth orbit sooner and safer. We look forward to a long
and mutually rewarding relationship and to expanding our presence in
Alabama," said Mark Sirangelo, head of Sierra Nevada Space Systems.
For more information about NASA Commercial Crew Program, visit:
http://www.nasa.gov/
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