Two black holes are entwined in a gravitational
tango in this artist's conception. Supermassive black holes at the hearts of
galaxies are thought to form through the merging of smaller, yet still massive
black holes, such as the ones depicted here.
Image Credit: NASA
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Astronomers have spotted what
appear to be two supermassive black holes at the heart of a remote galaxy,
circling each other like dance partners. The incredibly rare sighting was made
with the help of NASA's Wide-field Infrared Survey Explorer, or WISE.
Follow-up observations with the Australian Telescope Compact Array near
Narrabri, Australia, and the Gemini South telescope in Chile, revealed unusual
features in the galaxy, including a lumpy jet thought to be the result of one
black hole causing the jet of the other to sway.
"We think the jet of one black hole is being wiggled by the other, like a
dance with ribbons," said Chao-Wei Tsai of NASA's Jet Propulsion Laboratory,
Pasadena, Calif., who is lead author of a paper on the findings appearing in the
Dec. 10 issue of Astrophysical Journal. "If so, it is likely the two black holes
are fairly close and gravitationally entwined."
The findings could teach astronomers more about how supermassive black holes
grow by merging with each other.
The WISE satellite scanned the entire sky twice in infrared wavelengths
before being put into hibernation in 2011. NASA recently gave the spacecraft a
second lease on life, waking it up to search for asteroids, in a project called
NEOWISE.
The new study took advantage of previously released all-sky WISE data.
Astronomers sifted through images of millions of actively feeding supermassive
black holes spread throughout our sky before an oddball, also known as WISE
J233237.05-505643.5, jumped out.
"At first we thought this galaxy's unusual properties seen by WISE might mean
it was forming new stars at a furious rate," said Peter Eisenhardt, WISE project
manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and a co-author
of the study. "But on closer inspection, it looks more like the death spiral of
merging giant black holes."
Almost every large galaxy is thought to harbor a supermassive black hole
filled with the equivalent in mass of up to billions of suns. How did the black
holes grow so large? One way is by swallowing ambient materials. Another way is
through galactic cannibalism. When galaxies collide, their massive black holes
sink to the center of the new structure, becoming locked in a gravitational
tango. Eventually, they merge into one even-more-massive black hole.
The dance of these black hole duos starts out slowly, with the objects
circling each other at a distance of about a few thousand light-years. So far,
only a few handfuls of supermassive black holes have been conclusively
identified in this early phase of merging. As the black holes continue to spiral
in toward each other, they get closer, separated by just a few light-years.
It is these close-knit black holes, also called black hole binaries, that
have been the hardest to find. The objects are usually too small to be resolved
even by powerful telescopes. Only a few strong candidates have been identified
to date, all relatively nearby. The new WISE J233237.05-505643.5 is a new
candidate, and located much farther away, at 3.8 billion light-years from
Earth.
Radio images with the Australian Telescope Compact Array were key to
identifying the dual nature of WISE J233237.05-505643.5. Supermassive black
holes at the cores of galaxies typically shoot out pencil-straight jets, but, in
this case, the jet showed a zigzag pattern. According to the scientists, a
second massive black hole could, in essence, be pushing its weight around to
change the shape of the other black hole's jet.
Visible-light spectral data from the Gemini South telescope in Chile showed
similar signs of abnormalities, thought to be the result of one black hole
causing disk material surrounding the other black hole to clump. Together, these
and other signs point to what is probably a fairly close-knit set of circling
black holes, though the scientists can't say for sure how much distance
separates them.
"We note some caution in interpreting this mysterious system," said Daniel
Stern of JPL, a co-author of the study. "There are several extremely unusual
properties to this system, from the multiple radio jets to the Gemini data,
which indicate a highly perturbed disk of accreting material around the black
hole, or holes. Two merging black holes, which should be a common event in the
universe, would appear to be simplest explanation to explain all the current
observations."
The final stage of merging black holes is predicted to send gravitational
waves rippling through space and time. Researchers are actively searching for
these waves using arrays of dead stars called pulsars in hopes of learning more
about the veiled black hole dancers (see
The technical paper is online at
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages and operates the
WISE mission for NASA's Science Mission Directorate. The WISE mission was
selected competitively under NASA's Explorers Program managed by the agency's
Goddard Space Flight Center in Greenbelt, Md. The science instrument was built
by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by
Ball Aerospace & Technologies Corp. in Boulder, Colo. Science operations and
data processing take place at the Infrared Processing and Analysis Center at the
California Institute of Technology in Pasadena. Caltech manages JPL for NASA.
More information is online at http://www.nasa.gov/wise
and http://jpl.nasa.gov/wise
.
NASA
Guillermo Gonzalo Sánchez Achutegui
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