Caltech-Led
Astronomers Discover the Largest and Most Distant Reservoir of Water
Yet.
Water really is
everywhere. Two teams of astronomers, each led by scientists at the
California Institute of Technology (Caltech), have discovered the
largest and farthest reservoir of water ever detected in the universe.
Looking from a distance of 30 billion trillion miles away into a
quasar—one of the brightest and most violent objects in the cosmos—the
researchers have found a mass of water vapor that's at least 140
trillion times that of all the water in the world's oceans combined,
and 100,000 times more massive than the sun.
Because the quasar is so far away, its light has taken 12
billion years to reach Earth. The observations therefore reveal a time
when the universe was just 1.6 billion years old. "The environment
around this quasar is unique in that it's producing this huge mass of
water," says Matt Bradford, a scientist at NASA's Jet Propulsion
Laboratory (JPL), and a visiting associate at Caltech. "It's another
demonstration that water is pervasive throughout the universe, even at
the very earliest times." Bradford leads one of two international teams
of astronomers that have described their quasar findings in separate
papers that have been accepted for publication in the Astrophysical
Journal Letters.
A quasar is powered by an enormous black hole that is steadily
consuming a surrounding disk of gas and dust; as it eats, the quasar
spews out huge amounts of energy. Both groups of astronomers studied a
particular quasar called APM 08279+5255, which harbors a black hole 20
billion times more massive than the sun and produces as much energy as
a thousand trillion suns.
Since astronomers expected water vapor to be present even
in the early universe, the discovery of water is not itself a surprise,
Bradford says. There's water vapor in the Milky Way, although the total
amount is 4,000 times less massive than in the quasar, as most of the
Milky Way’s water is frozen in the form of ice.
Nevertheless, water vapor is an important trace gas that
reveals the nature of the quasar. In this particular quasar, the water
vapor is distributed around the black hole in a gaseous region spanning
hundreds of light-years (a light-year is about six trillion miles), and
its presence indicates that the gas is unusually warm and dense by
astronomical standards. Although the gas is a chilly –53 degrees
Celsius (–63 degrees Fahrenheit) and is 300 trillion times less dense
than Earth's atmosphere, it's still five times hotter and 10 to 100
times denser than what's typical in galaxies like the Milky Way.
The water vapor is just one of many kinds of gas that
surround the quasar, and its presence indicates that the quasar is
bathing the gas in both X-rays and infrared radiation. The interaction
between the radiation and water vapor reveals properties of the gas and
how the quasar influences it. For example, analyzing the water vapor
shows how the radiation heats the rest of the gas. Furthermore,
measurements of the water vapor and of other molecules, such as carbon
monoxide, suggest that there is enough gas to feed the black hole until
it grows to about six times its size. Whether this will happen is not
clear, the astronomers say, since some of the gas may end up condensing
into stars or may be ejected from the quasar.
Bradford's team made their observations starting in 2008,
using an instrument called Z-Spec at the Caltech Submillimeter
Observatory (CSO),
a 10-meter telescope near the summit of Mauna Kea in Hawaii. Z-Spec is
an extremely sensitive spectrograph, requiring temperatures cooled to
within 0.06 degrees Celsius above absolute zero. The instrument
measures light in a region of the electromagnetic spectrum called the
millimeter band, which lies between infrared and microwave wavelengths.
The researchers' discovery of water was possible only because Z-Spec’s
spectral coverage is 10 times larger than that of previous
spectrometers operating at these wavelengths. The astronomers made
follow-up observations with the Combined Array for Research in
Millimeter-Wave Astronomy (CARMA), an array of radio dishes in the Inyo
Mountains of Southern California.
This discovery highlights the benefits of observing in the
millimeter and submillimeter wavelengths, the astronomers say. The
field has developed rapidly over the last two to three decades, and to
reach the full potential of this line of research, the
astronomers—including the study authors—are now designing CCAT, a
25-meter telescope to be built in the Atacama Desert in Chile. CCAT
will allow astronomers to discover some of the earliest galaxies in the
universe. By measuring the presence of water and other important trace
gases, astronomers can study the composition of these primordial
galaxies.
The second group, led by Dariusz Lis, senior research
associate in physics at Caltech and deputy director of the CSO, used the Plateau de
Bure Interferometer in the French Alps to find water. In 2010, Lis's
team was looking for traces of hydrogen fluoride in the spectrum of APM
08279+5255, but serendipitously detected a signal in the quasar's
spectrum that indicated the presence of water. The signal was at a
frequency corresponding to radiation that is emitted when water
transitions from a higher energy state to a lower one. While Lis's team
found just one signal at a single frequency, the wide bandwidth of
Z-Spec enabled Bradford and his colleagues to discover water emission
at many frequencies. These multiple water transitions allowed
Bradford's team to determine the physical characteristics of the
quasar's gas and the water's mass.
The other authors on Lis's paper, "Discovery of water
vapor in the high-redshift quasar APM 08279+5255 at Z=3.91," are Tom
Phillips, Caltech's John D. MacArthur Professor of Physics and director
of the CSO; David
Neufeld of Johns Hopkins University; Maryvonne Gerin of the Paris
Observatory and the French National Center for Scientific Research; and
Roberto Neri of the Institute of Millimeter Radio Astronomy in France.
Funding was provided by the National Science Foundation (NSF).
The authors on Bradford's paper, "The water vapor spectrum
of APM 08279+5255: X-ray heating and infrared pumping over hundreds of
parsecs," include Caltech's Hien Nguyen, a visiting associate and
lecturer in physics; Jamie Bock, senior faculty associate in physics
and scientist at JPL; and Jonas Zmuidzinas, the Merle Kingsley
Professor of Physics and chief technologist at JPL. The other authors
are Alberto Bolatto of the University of Maryland, College Park; Philip
Maloney, Jason Glenn, and Julia Kamenetzky of the University of
Colorado, Boulder; James Aguirre, Roxana Lupu, and Kimberly Scott of
the University of Pennsylvania; Hideo Matsuhara of the Institute of
Space and Astronautical Science in Japan; Eric Murphy of the Carnegie
Institution for Science; and Bret Naylor of JPL.
Funding for Z-Spec was provided by the NSF, NASA, the
Research Corporation, and partner institutions. The CSO is operated by
Caltech under contract from the NSF. CARMA was built and is operated by
Caltech, UC Berkeley, the University of Maryland, College Park, the
University of Illinois at Urbana-Champaign, and the University of
Chicago. CARMA is funded by a combination of state and private sources,
as well as the NSF and its University Radio Observatories program.
Written by Marcus Woo
Deborah Williams-Hedges
626-395-3227
debwms@caltech.edu
Caltech's press
release
Figure
1. This artist's concept illustrates a quasar, or feeding
black hole, similar to APM 08279+5255, where astronomers discovered
huge amounts of water vapor. Gas and dust likely form a torus around
the black hole, with clouds of charged gas above and below. X-rays
emerge from the center, while dust throughout the torus emits infrared
radiation. While this figure shows the quasar's torus approximately
edge-on, the torus around APM 08279+5255 is likely positioned face-on
from our point of view.
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