This image shows galaxies clumped together in the
Fornax cluster, located 60 million light-years from Earth. The picture was taken
by WISE, but has been artistically enhanced to illustrate the idea that clumped
galaxies will, on average, be surrounded by larger halos of dark matter
(purple).
Image Credit:
NASA/JPL-Caltech
Feature Link:
This infographic explains a popular theory of
active supermassive black holes, referred to as the unified model -- and how new
data from NASA's Wide-field Infrared Survey Explorer, or WISE, is at conflict
with the model.
Image Credit:
NASA/JPL-Caltech/NOAO/AURA/NSF/ESO
Feature Link:
A survey of more than 170,000 supermassive black holes, using NASA's
Wide-field Infrared Survey Explorer (WISE), has astronomers reexamining a
decades-old theory about the varying appearances of these interstellar
objects.
The unified theory of active, supermassive black holes, first developed in
the late 1970s, was created to explain why black holes, though similar in
nature, can look completely different. Some appear to be shrouded in dust, while
others are exposed and easy to see.
The unified model answers this question by proposing that every black hole is
surrounded by a dusty, doughnut-shaped structure called a torus. Depending on
how these "doughnuts" are oriented in space, the black holes will take on
various appearances. For example, if the doughnut is positioned so that we see
it edge-on, the black hole is hidden from view. If the doughnut is observed from
above or below, face-on, the black hole is clearly visible.
However, the new WISE results do not corroborate this theory. The researchers
found evidence that something other than a doughnut structure may, in some
circumstances, determine whether a black hole is visible or hidden. The team has
not yet determined what this may be, but the results suggest the unified, or
doughnut, model does not have all the answers.
"Our finding revealed a new feature about active black holes we never knew
before, yet the details remain a mystery," said Lin Yan of NASA's Infrared
Processing and Analysis Center (IPAC), based at the California Institute of
Technology in Pasadena. "We hope our work will inspire future studies to better
understand these fascinating objects."
Yan is the second author of the research accepted for publication in the
Astrophysical Journal. The lead author is post-doctoral researcher, Emilio
Donoso, who worked with Yan at IPAC and has since moved to the Instituto de
Ciencias Astronómicas, de la Tierra y del Espacio in Argentina. The research
also was co-authored by Daniel Stern at NASA's Jet Propulsion Laboratory (JPL)
in Pasadena, and Roberto Assef of Universidad Diego Portales in Chile and
formerly of JPL.
Every galaxy has a massive black hole at its heart. The new study focuses on
the "feeding" ones, called active, supermassive black holes, or active galactic
nuclei. These black holes gorge on surrounding gas material that fuels their
growth.
With the aid of computers, scientists were able to pick out more than 170,000
active supermassive black holes from the WISE data. They then measured the
clustering of the galaxies containing both hidden and exposed black holes -- the
degree to which the objects clump together across the sky.
If the unified model was true, and the hidden black holes are simply blocked
from view by doughnuts in the edge-on configuration, then researchers would
expect them to cluster in the same way as the exposed ones. According to theory,
since the doughnut structures would take on random orientations, the black holes
should also be distributed randomly. It is like tossing a bunch of glazed
doughnuts in the air -- roughly the same percentage of doughnuts always will be
positioned in the edge-on and face-on positions, regardless of whether they are
tightly clumped or spread far apart.
But WISE found something totally unexpected. The results showed the galaxies
with hidden black holes are more clumped together than those of the exposed
black holes. If these findings are confirmed, scientists will have to adjust the
unified model and come up with new ways to explain why some black holes appear
hidden.
"The main purpose of unification was to put a zoo of different kinds of
active nuclei into a single umbrella," said Donoso. Now, that has become
increasingly complex to do as we dig deeper into the WISE data."
Another way to understand the WISE results involves dark matter. Dark matter
is an invisible substance that dominates matter in the universe, outweighing the
regular matter that makes up people, planets and stars. Every galaxy sits in the
center of a dark matter halo. Bigger halos have more gravity and, therefore,
pull other galaxies toward them.
Because WISE found that the obscured black holes are more clustered than the
others, the researchers know those hidden black holes reside in galaxies with
larger dark matter halos. Though the halos themselves would not be responsible
for hiding the black holes, they could be a clue about what is occurring.
"The unified theory was proposed to explain the complexity of what
astronomers were seeing," said Stern. "It seems that simple model may have been
too simple. As Einstein said, models should be made 'as simple as possible, but
not simpler.'"
Scientists still are actively combing public data from WISE, put into
hibernation in 2011 after scanning Earth's entire sky twice. WISE was
reactivated in 2013, renamed NEOWISE, and given a new mission to identify
potentially hazardous near-Earth objects.
For more information about NEOWISE, visit:
For more information about WISE, visit:
NASA
Guillermo Gonzalo Sánchez Achutegui
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