Using the National Science Foundation’s Very Large
Array (VLA) radio telescope and helped by a gigantic
cosmic lens conveniently provided by nature, an
international team of astronomers has discovered that
a young galaxy had a central disk of gas in which
hundreds of new stars were being born every
year — at a time when the Universe was only a fraction
of its current age.

“This unique look into a very distant, young galaxy
gives us unprecedented insight into the process that
produced both tremendous numbers of stars and
supermassive black holes in forming galaxies,” said
Chris Carilli, of the National Radio Astronomy
Observatory (NRAO) in Socorro, NM, leader of the
research team. “This work strongly supports the idea
that the stars and the black holes formed simultaneously,”
he added. The research was published in the April 4 issue
of Science Express.

The astronomers studied a quasar called PSS J2322+1944,
about 12 billion light-years from Earth. The quasar
is an extremely luminous object powered by the supermassive
black hole at the core of a galaxy. At the distance of this
quasar, the scientists see the object as it was when the
Universe was less than 2 billion years old, about 15 percent
of its current age.

The discovery required a huge assist from nature.
To find the star-forming disk, the astronomers needed
to observe natural radio emission from the carbon
monoxide (CO) molecule, an important component of the
gas that forms stars. However, this molecule emits
radio waves at frequencies much higher than the VLA
is capable of receiving. At PSS J2322+1944’s
distance of 12 billion light-years, however, the expansion
of the Universe stretched the radio waves, reducing their
frequency. CO emission at 230 GigaHertz was shifted to 45
GigaHertz, within the VLA’s range.

That alone was not enough. The distance that made it
possible to receive the radio waves from the quasar also
meant that the object was too far away for the VLA to
discern the detail required to show the disk. Once again,
nature stepped in to help, providing another galaxy directly
between the quasar and Earth to form a gravitational
lens.

“What we needed wasn’t just any old gravitational lens,
but a nearly-perfect alignment of the distant quasar,
mid-distance galaxy, and Earth — and that’s what we got,”
said Geraint Lewis of the University of Sydney in Australia,
another member of the team. With such a perfect
alignment, the quasar image was distorted into a ring,
called an “Einstein Ring.” The VLA images were the first
to show the Einstein Ring of PSS J2322+1944.

“We never would have seen the disk of CO gas near the
center of this galaxy without the gravitational lens,”
said Carilli. “The lens boosted the signal and
magnified the image to reveal the disk’s structure
in unprecedented detail,” he added.

For several years, astronomers have noted that the masses
of black holes are directly proportional to the sizes
of central bulges of stars in galaxies. This led to
the speculation that formation of the black holes and of
the stars are somehow related to each other. Scientists
hypothesized that gas being drawn towards a galaxy’s central
black hole is the same gas from which large numbers of
stars are forming.

Studies of more-nearby galaxies supported such speculation,
but the question remained whether the idea could be
applied to the very early Universe, when the first
galaxies and black holes formed.

“This new observation gives strong support to the idea
that large numbers of stars were forming in young galaxies
at the same time that their central black holes were
pulling in additional mass,” said Pierre Cox, of the
Institute for Space Astrophysics of the University
of Paris.

The astronomers believe that galaxies in the early
Universe were frequently disrupted by nearby encounters
with other galaxies, “feeding” the central black hole
with gas. The gas formed an extensive, spinning disk
around the galaxy’s center, some of it eventually
falling into the black hole and some of it forming new
stars.

In PSS J2322+1944, the astronomers believe that new
stars with a total mass equal to some 900 times that of
the Sun were forming in the 13,000-light-year-diameter
disk every year. At that rate, the scientists say, most
of the stars in a large elliptical galaxy could form in
only about 100 million years.

PSS J2322+1944 is one of the most luminous quasars in
the Universe. It was first discovered by George
Djorgovski of the California Institute of Technology
(Caltech), using the digitized Palomar Observatory Sky
Survey. Later studies led by Cox and Alain Omont of the
Astrophysical Institute of Paris using the IRAM
millimeter-wave facilities in Europe (the 30-meter
telescope and the Plateau de Bure Interferometer)
showed that it had a huge reservoir of dust and
molecular gas, the fuel for star formation. Optical
observation at the W.M. Keck Observatory in Hawaii showed
a double image that indicated gravitational lensing. All
these factors, the scientists said, made it an ideal
candidate for study with the VLA.

“Our guess paid off handsomely. Finding that Einstein
Ring with the VLA gave us the tool we needed to see
what was going on inside that very distant galaxy,”
said Carilli. “There are fewer than 100 gravitational
lenses known so far, and we were extremely lucky to find
one that allowed us to help resolve the specific scientific
question we were studying.”

Gravitational lenses were predicted, based on Albert
Einstein’s General Theory of Relativity, in 1919. Einstein
himself showed in 1936 that a perfectly-aligned gravitational
lens would produce a circular image, but felt that the
chances of actually observing such an object were nearly
zero. The first gravitational lens was discovered in
1979, and the first Einstein Ring was discovered by
researchers using the VLA in 1987. PSS J2322+1944 is the
first Einstein Ring detected through the signature
emission of a molecule and the most distant yet found.

PSS J2322+1944 may be able to make another contribution
to science. Astronomers believe that gravitational
lenses may serve as a tool for precisely measuring great
distances in the Universe. If a distant quasar varies
in brightness over time, the multiple images formed by
a gravitational lens would show that variation at
different times. By monitoring such time differences
and using a mathematical model of the specific gravitational
lens, the distance to the quasar can be measured.

“This quasar, if it shows brightness variations in the
future, may be such a ‘Golden Lens,’ long sought to
refine our measurement of very great distances,” said
Lewis.

In addition to Carilli, Lewis, Djorgovski, Cox and Omont,
the research team includes Ashish Mahabal of Caltech and
Frank Bertoldi of the Max-Planck Institute for Radio
Astronomy in Bonn, Germany.

The National Radio Astronomy Observatory is a facility
of the National Science Foundation, operated under
cooperative agreement by Associated Universities, Inc.