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Radio/Optical combination images of distant galaxies as seen with NSF's Very Large Array and NASA's Hubble Space Telescope. Their distances from Earth are indicated in the top set of images. Below, the same images, without labels. Credit: K. Trisupatsilp, NRAO/AUI/NSF, NASA.
Astronomers have gotten their first look at exactly where most of
today's stars were born. To do so, they used the National Science
Foundation's Karl G. Jansky Very Large Array (VLA) and the Atacama Large
Millimeter/submillimeter Array (ALMA) to look at distant galaxies seen
as they were some 10 billion years ago.
At that time, the Universe was experiencing its peak rate of star formation. Most stars in the present Universe were born then.
knew that galaxies in that era were forming stars prolifically, but we
didn't know what those galaxies looked like, because they are shrouded
in so much dust that almost no visible light escapes them," said Wiphu
Rujopakam, of the Kavli Institute for the Physics and Mathematics of the
Universe at the University of Tokyo and Chulalongkorn University in
Bangkok, who was lead author on the research paper.
unlike visible light, can get through the dust. However, in order to
reveal the details of such distant -- and faint -- galaxies, the
astronomers had to make the most sensitive images ever made with the
The new observations, using the VLA and ALMA, have answered
longstanding questions about just what mechanisms were responsible for
the bulk of star formation in those galaxies. They found that intense
star formation in the galaxies they studied most frequently occured
throughout the galaxies, as opposed to much smaller regions in
present-day galaxies with similar high star-formation rates.
astronomers used the VLA and ALMA to study galaxies in the Hubble Ultra
Deep Field, a small area of sky observed since 2003 with NASA's Hubble
Space Telescope (HST). The HST made very long exposures of the area to
detect galaxies in the far-distant Universe, and numerous observing
programs with other telescopes have followed up on the HST work.
used the VLA and ALMA to see deeply into these galaxies, beyond the
dust that obscured their innards from Hubble," said Kristina Nyland, of
the National Radio Astronomy Observatory (NRAO). "The VLA showed us
where star formation was occurring, and ALMA revealed the cold gas that
is the fuel for star formation," she added.
"In this study, we
made the most sensitive image ever made with the VLA," said Preshanth
Jagannathan, also of NRAO. "If you took your cellphone, which transmits a
weak radio signal, and put it at more than twice the distance to Pluto,
near the outer edge of the solar system, its signal would be roughly as
strong as what we detected from these galaxies," he added.
study of the galaxies was done by an international team of astronomers.
Others involved include James Dunlop of the University of Edinburgh and
Rob Ivison of the University of Edinburgh and the European Southern
Observatory. The researchers reported their findings in the Dec. 1 issue
of the Astrophysical Journal.
ALMA is a partnership of
ESO (representing its member states), NSF (USA) and NINS (Japan),
together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic
of South Korea), in cooperation with the Republic of Chile. The Joint
ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ.
National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated