Maunakea, Hawaii – Using the W. M. Keck Observatory in Hawaii, a group of astronomers led by Joseph Hennawi of the Max Planck Institute for Astronomy have discovered the first quadruple quasar: four rare active black holes situated in close proximity to one another. The quartet resides in one of the most massive structures ever discovered in the distant universe, and is surrounded by a giant nebula of cool dense gas. Because the discovery comes with one-in-ten-million odds, perhaps cosmologists need to rethink their models of quasar evolution and the formation of the most massive cosmic structures. The results are being published in the May 15, 2015 edition of the journal Science.
Hitting the jackpot is one
thing, but if you hit the jackpot four times in a row you might wonder if the
odds were somehow stacked in your favor.
Quasars constitute a brief
phase of galaxy evolution, powered by the in-fall of matter onto a supermassive
black hole at the center of a galaxy. During this phase, they are the most
luminous objects in the Universe, shining hundreds of times brighter than their
host galaxies, which themselves contain hundreds of billions of stars. But
these hyper-luminous episodes last only a tiny fraction of a galaxy’s lifetime,
which is why astronomers need to be very lucky to catch any given galaxy in the
act. As a result, quasars are exceedingly rare on the sky, and are typically
separated by hundreds of millions of light years from one another. The
researchers estimate that the odds of discovering a quadruple quasar by chance
is one in ten million. How on Earth did they get so lucky?
Clues come from peculiar
properties of the quartet’s environment. The four quasars are surrounded by a
giant nebula of cool dense hydrogen gas, which emits light because it is
irradiated by the intense glare of the quasars. In addition, both the quartet
and the surrounding nebula reside in a
rare corner of the universe with a surprisingly large amount of matter. “There
are several hundred times more galaxies in this region than you would expect to
see at these distances,” said J. Xavier Prochaska, professor at the University
of California Santa Cruz and the principal investigator of the Keck Observatory
observations.
Given the exceptionally large
number of galaxies, this system resembles the massive agglomerations of
galaxies, known as galaxy clusters, that astronomers observe in the present-day
universe. But because the light from this cosmic metropolis has been travelling
for 10 billion years before reaching Earth, the images show the region as it
was 10 billion years ago, less than 4 billion years after the big bang. It is
thus an example of a progenitor or ancestor of a present-day galaxy cluster, or
proto-cluster for short.
Piecing all of these
anomalies together, the researchers tried to understand what appears to be
their incredible stroke of luck. “If you discover something which, according to
current scientific wisdom should be extremely improbable, you can come to one
of two conclusions: either you just got very lucky, or you need to modify your
theory,” Hennawi said.
The researchers speculate
that some physical process might make quasar activity much more likely in
specific environments. One possibility is that quasar episodes are triggered
when galaxies collide or merge, because these violent interactions efficiently
funnel gas onto the central black hole. Such encounters are much more likely to
occur in a dense proto-cluster filled with galaxies, just as one is more likely
to encounter traffic when driving through a big city.
“The giant emission nebula is an important piece of the puzzle since it
signifies a tremendous amount of dense cool gas,” said Fabrizio
Arrigoni-Battaia, a PhD student at the Max Planck Institute for Astronomy who
was involved in the discovery.
Supermassive black holes can
only shine as quasars if there is gas for them to swallow, and an environment
that is gas rich could provide favorable conditions for fueling quasars.
On
the other hand, given the
current understanding of how massive structures in the universe form,
the
presence of the giant nebula in the proto-cluster is totally unexpected.
“Our
current models of cosmic structure formation based on supercomputer
simulations
predict that massive objects in the early universe should be filled with
rarefied gas that is about ten million degrees, whereas this giant
nebula
requires gas thousands of times denser and colder,” said Sebastiano
Cantalupo, currently at ETH Zurich, that led the imaging observations a
the Keck Observatory during his previous research appointment at UCSC.
“It is really amazing that this discovery was made the same night of
the Slug Nebula
while we were hunting for giant Lyman alpha nebulae illuminated by
quasars – my first night at Keck Observatory and definitely the most
exciting observing night I have ever had!”
“Extremely rare events have
the power to overturn long-standing theories” Hennawi said.
As such, the discovery of the
first quadruple quasar may force cosmologists to rethink their models of quasar
evolution and the formation of the most massive structures in the universe.
The
authors wish to recognize and acknowledge the very significant cultural role
and reverence that the summit of Mauna Kea has always had within the indigenous
Hawaiian community. We are most fortunate to have the opportunity to
conduct observations from this mountain.
The W. M. Keck Observatory operates the
largest, most scientifically productive telescopes on Earth. The two, 10-meter
optical/infrared telescopes near the summit of Mauna Kea on the Island of
Hawaii feature a suite of advanced instruments including imagers, multi-object
spectrographs, high-resolution spectrographs, integral-field spectrographs and
world-leading laser guide star adaptive optics systems.
The Low Resolution Imaging Spectrometer (LRIS) is a very
versatile visible-wavelength imaging and spectroscopy instrument commissioned
in 1993 and operating at the Cassegrain focus of Keck I. Since it has been
commissioned it has seen two major upgrades to further enhance its
capabilities: addition of a second, blue arm optimized for shorter wavelengths
of light; and the installation of detectors that are much more sensitive at the
longest (red) wavelengths. Each arm is optimized for the wavelengths it covers. This
large range of wavelength coverage, combined with the instrument's high
sensitivity, allows the study of everything from comets (which have interesting
features in the ultraviolet part of the spectrum), to the blue light from star
formation, to the red light of very distant objects. LRIS also records the
spectra of up to 50 objects simultaneously, especially useful for studies of
clusters of galaxies in the most distant reaches, and earliest times, of the
universe.
Keck Observatory is a private 501(c) 3
non-profit organization and a scientific partnership of the California
Institute of Technology, the University of California and NASA.
SCIENCE CONTACT:
Joseph F.Hennawi
Max Planck Institute for Astronomy, Heidelberg, Germany
joe@mpia.de
+49 6221 528 -263
J. Xavier Prochaska
UCO Lick Observatory/University of California Santa Cruz
xavier@ucolick.org
+1 831 459 2135
Sebastiano Cantalupo
ETH Zurich, Switzerland
cantalupo@phys.ethz.ch
+41 44 633 7057
MEDIA CONTACT:
Markus Pössel
Public Information Officer
Max Planck Institute for Astronomy, Heidelberg, Germany
pr@mpia.de
+49 6221 528 -261
Steve Jefferson
Communications Officer
W. M. Keck Observatory
sjefferson@keck.hawaii.edu
+1 808 881 3827
Source: W.M. Keck Observatory
