Questions & Answers:
The Most Distant Galaxy In The Universe
What was discovered?
An international team of astronomers has discovered the most distant galaxy
found in the universe to date.
How far away is it?
The galaxy is so far away that its light is only reaching us now from a time
when the universe was but 7% of its current age of approximately 14 billion
years. This places the young galaxy as far as 13 billion light-years from
us, and far back in time during the "formative years" of galaxy birth and
evolution.
What telescopes were used?
The team of astronomers made observations by combining the unique sharpness
of the images from NASA's Hubble Space Telescope with the light-collecting
power of the W. M. Keck Telescopes -- and with an added boost from a
gravitational lens in space.
Who made the discovery?
Marijn Franx, Pieter van Dokkum (Kapteyn Institute, University of Groningen,
The Netherlands); Garth Illingworth, Dan Kelson, Kim-Vy Tran (the
University of California Observatories/Lick Observatory, University of
California, Santa Cruz, California).
Why do the astronomers consider the discovery so significant?
"When we received the Hubble image, we immediately knew that we had found
something special", says Marijn Franx. "We were excited by the possibility
that we may have found a unique example of a galaxy in formation at the
time of the earliest quasars".
"We are fascinated to be witnessing the very early stages of the
construction of what could well become a massive galaxy like our own Milky
Way", says Garth Illingworth of University of California, Santa Cruz. "This
object is a pathfinder for deciphering what is happening in young galaxies,
and offers a rare glimpse of the powerful events that transpired during the
formation of galaxies".
What does it look like?
Hubble shows that bright dense knots of massive stars power this object.
Because of the firestorm of starbirth within it, the galaxy is intrinsically
one of the brightest young galaxies in the universe, blazing with the
brilliance of more than 10 times our own Milky Way. The object is similar
to what Hubble sees in nearby starburst galaxies, though it is a very
extreme and dramatic example.
What is a gravitational lens?
Predicted by Einstein's theory of general relativity, gravitational lenses
are collections of matter (such as clusters of galaxies) that are so
massive they warp space in their vicinity, allowing the light of even
more-distant objects to curve around the central lens-mass and be seen from
Earth as magnified objects.
Why do telescopes need the help of a gravitational lens?
The object is so far away, observing it in such detail would tax the
capabilities of both Hubble and Keck without the magnification of the
gravitational lens provided by a foreground cluster of galaxies that is
much closer to us, at 5 billion light-years.
How did the astronomers know it was a lensed object?
A telltale sign of the lensing is the fact the remote galaxy's image is
smeared into an arc-shape by the gravitational influence of the intervening
galaxy cluster. The smeared image of the galaxy stood out because of its
unusual reddish color, never observed in such galaxies before.
Why is it colored red?
The special color of the galaxy in the arc, is due to absorption by the
matter in the universe between us and the galaxy, suggesting it was at a
great distance.
How did the astronomers prove it's so far away?
The suspected remoteness of the lensed object was confirmed when the team of
astronomers made spectroscopic observations with one of the twin Keck
telescopes on Mauna Kea, Hawaii, to measure its redshift (4.92), which is
a measure of the expansion of space (due to the Big Bang); the larger the
redshift, the greater space has expanded between us and the object. This
can be used to estimate its distance.
Haven't more distant objects been seen?
Though candidates for still more distant galaxies have been proposed, they
have not been confirmed spectroscopically.
What does the galaxy really look like?
The researchers used a theoretical model of the effects of the gravitational
lens to "unsmear" the galaxy back into its normal appearance. The corrected
image clearly shows several bright, very compact regions of intense star
formation.
Why are these knots so interesting?
The stellar knots could be the building blocks that eventually assembled to
form the hub of a galaxy, like the central region of our Milky Way. The
tiny, 700 light-year-sized stellar knots are scattered over a region that
is only about 15,000 light-years across, only about a quarter the diameter
of our Milky Way galaxy.
What do the knots tell us about early galaxy formation?
"Based on this image we can begin to make some conclusions about the early
growth of galaxies", says Illingworth. "The knots show that starbirth
happens in very tiny regions compared with the size of the final galaxy".
This helps clarify the astronomer's view of the formation of galaxies as
occurring within a cauldron of hot gas, with knots of intense star
formation, strong winds, and "mergers" -- collisions of the dense
star-forming knots.
What else has been learned?
Using Keck's spectroscopic capabilities, the astronomers have also, for the
first time, been able to measure the motions of the gas within such a
distant galaxy. The observations reveal a nearly half million mile per hour
"wind" -- an outflow of gas, presumably accelerated by energy from
supernova explosions going off like a string of firecrackers.
What does the "wind" tell us about early star formation?
"The strong winds that we observe, suggest that galaxies may lose a lot of
material when they are young and thereby enrich the empty space around
them", says Franx. "Many astronomers had speculated about the existence of
such winds in such distant galaxies, and we now have an object where we can
see them directly. It is striking that the most distant galaxy found to
date is also the one that provides us the most detailed picture of events
in such distant galaxies".
Updated: August 9 '97
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