A Race Around a Black Hole
So you think rockets are fast? Scientists have spotted something
going much faster. Like state troopers on a highway, these scientists
used a "speed gun" to clock clumps of hot iron gas whipping around a
black hole at 20,000 miles per second - over 10 percent of light
speed. At that speed, you could get to the moon in about 10 seconds.
Dr. Jane Turner of NASA Goddard Space Flight Center led the
observation. She used the XMM-Newton satellite, launched by the
European Space Agency. She said that this kind of measurement has
never been done before.
For years we have seen only the general commotion caused by massive
black holes, that is, a terrific outpouring of light," Dr. Turner
said. "We could not track the specifics. Now we can filter through all
that light and find patterns that reveal information about black holes
never seen before in such clarity."
This animation shows three hot
blobs of matter orbiting a black hole.
(Click on image
to view 4.8 MB animation)
(Credit: NASA/Dana Berry, Skyworks Digital)
This is big news for black hole hunters because the observation marks
the first time scientists could trace individual blobs of shredded
matter on a complete journey around a black hole. This provides a
crucial measurement that has long been missing from black hole
studies: an orbital period. Knowing this, scientists can measure black
hole mass and other characteristics that have long eluded them.
If this black hole were placed in our Solar System, it would appear
like a dark abyss spread out nearly as wide as Mercury's orbit. And
the clumps of matter detected would be as far out as Jupiter. The
clumps orbit the black hole in a lightning-quick 27 hours (compared to
the 12 years it takes Jupiter to orbit the Sun).
But this black
hole is far, far away. Dr. Turner's team observed it in a well-known
galaxy named Markarian 766, about 170 million light years away in the
constellation Coma Berenices (Bernice's Hair). The black hole in
Markarian 766 is relatively small although highly active. Its mass is
a few million times that of the Sun. Other central black hole systems
are over 100 million solar masses.
Matter funnels into this black
hole like water swirling down a drain, forming what scientists call an
accretion disk. Flares erupt on this disk most likely when magnetic
field lines emanating from the central black hole interact with
regions on the disk. Zap! These flares are very hot. They glow in
X-ray light, which is thousands of times more energetic that the
visible light our eyes can detect.
This animation shows how scientists
track hot material around a black hole via spectral emission lines
(Click on image to view 2.5 MB animation.
(Credit: NASA/Dana Berry, Skyworks Digital)
Calculating the speeds of the
flares and the black hole mass was straightforward, based on Doppler shifting, the technique used by law officers to nab speeders." said
Dr. Ian George of NASA Goddard. (Both Drs. Turner and George hold
teaching positions at the University of Maryland, Baltimore County.)
"Light appears to rise in energy as an object moves toward us and
then fall in energy as it moves away. A similar phenomenon happens
with the sound of a passing car on a highway, going
Plot of peak X-ray energy vs time
for three different blobs of matter in the disk around the black
hole in Markarian 766.
(Credit: Jane Turner and Lance Miller)
When the scientists made a graph of energy (on the
y-axis) and time (on the x-axis), they saw near-perfect sinusoidal
curves from each of the three clumps of matter they observed. Up and
down, up and down. The width (or period) of the curves is proportional
to black hole mass. The height (or amplitude) of the curves is related
to the viewing angle of the accretion disk.
With a known mass and
orbital period, the scientists could determine velocity using the
relatively simple and traditional physics of Isaac Newton. Scientists
do these kinds of measurements in the Solar System all the time. For
example, if the Sun were bigger or if the Earth were closer to the
Sun, our orbit would be faster because the tug of gravity would be
stronger. That is, mass, distance and gravity dictate the speed and
shape of orbits. Knowing one set of information helps you determine
Two factors made the black hole measurement
possible. The scientists observed particularly persistent flares
during a long observation, nearly 27 hours. Also, no telescope before
XMM-Newton has had the light-collecting power to allow for a
comparison of energy over time.
Dr. Turner said this observation confirms a preliminary XMM-Newton
result announced by a European team in September - that something as
detailed as an orbital period could be detected with the current
generation of X-ray telescopes. The combination of results indicates
that scientists, given long observation times, are now able to
make careful black hole measurements and even test general
relativity in the domain of extreme gravity.
And moving 20,000 miles per second, these blobs around the black hole are taking scientists on an exciting ride.