How the light bends around the intervening object to magnify the black hole behind it. ESA/ATG medialab
The
inner regions of a black hole have been observed by a team of
scientists, but not through the power of telescopes alone. Researchers
at the European Space Agency have tapped into gravitational lensing to
learn more about these mysterious objects -- in particular, a
supermassive black hole by the name of PKS 1830-211, some 11 billion
light-years away and one of the most powerful known objects of its kind.
"From
Earth, black holes are tiny. They're just so very far away. Trying to
observe PKS 1830-211 is like trying to look at an ant sitting on the
Moon," said lead author Andrii Neronov of the University of Geneva,
Switzerland. His team's paper was published this week in the journal
Nature Physics.
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"None
of our telescopes can observe something so small, so we used a trick to
resolve the ant: a huge gravitational lens," Neronov said.
Gravitational
lenses occur when a high-mass object, such as a galaxy or galaxy
cluster, between the viewer and the target pulls light in a curve in
such a way that it magnifies what is behind it.
The
Integral,
Fermi and
Swift
space telescopes in orbit around the Earth were turned on the
gravitational lens between Earth and PKS 1830-211 to study the area
around the black hole.
What
the team of astronomers was looking for in particular was to study the
behaviour of the gamma rays around the black hole -- highly energetic
radiation emitted by some of the most powerful objects in the universe.
Around black holes, gamma rays move around at close to the speed of
light, thought to be emitted from the wild spin of superheated material
as it is devoured by the black hole.
Our
current telescopes, however, are not powerful enough to see clearly
into these regions, which means it is difficult to understand what is
happening.
Simulation
of the lensing effect, with the black hole shown in red and the white
areas representing the areas of magnification and distortion due to
gravitational lensing. Courtesy of A. Neronov, ISDC, University of Geneva, Switzerland
PKS
1830-211 was the perfect candidate for this research. The object was
identified as a particularly strongly lensed object back
in 1991, and the European Southern Observatory
released research in 2013 wherein astronomers had observed PKS 1830-211 through a gravitational lens.
However,
this is the first time astronomers have attempted to use a
gravitational lens to examine black hole gamma ray activity, observing a
patch of sky about 100 times the distance between the Earth and sun in
size.
Using
the combined might of the telescopes and the gravitational lens, the
team was able to resolve the region, getting a more detailed view of the
radiation.
Fermi
detected the more energetic gamma rays, coming from the tiny base of
the gamma ray jet. The lower energy gamma rays, detected by Integral,
were emitted from the much larger surrounding region. Integral and Swift
were also used to examine X-rays found to be emanating from a region
some 400 billion kilometres around the black hole.
"Our
observations demonstrate that the gamma rays come from the direct
vicinity of the black hole itself. This gives us some idea about what is
and isn't important in generating the jets," Neronov said.
"It's
amazing to be able to see such tiny things at such enormous distances
from us. I'm very excited to have a 'black-hole-scope' to investigate
the inner regions of the jets."
