September 17, 1997

The Most Distant Galaxy

The reddish arc within the rectangle in the above image is the most distant galaxy ever observed. The light that produced this image left the galaxy roughly 13 billion years ago, when the universe was merely a billion years old. The image gives us clues as to what the universe was like when its first structures -- the first stars, star clusters, and galaxies -- began to form.

Most of the other features seen in the large image above are galaxies belonging to a foreground cluster of galaxies, CL1358+62, which is at the "modest" distance of 5 billion light-years.

The international team of astronomers who made this discovery (they and their institutions are listed under image credit above) used three telescopes, two made by man and one provided by nature:

The two man-made telescopes were NASA's Hubble Space Telescope (HST), whose unique sharpness allowed the team to take the above image, and the W. M. Keck Observatory on top of Mauna Kea in Hawaii, whose large size and light-gathering power allowed them to measure the redshift of the galaxy's light and determine its distance.

The telescope provided by nature is the cluster CL1358+62, which acts as a gravitational lens. The cluster's great mass warps space in its vicinity and bends the light of the more distant galaxy as it passes by, somewhat akin to the way a magnifying glass here on Earth bends light and magnifies objects. This gravitational bending distorts the galaxy's image into the arc seen in the image and magnifies it.

The gravitational magnification of the distant galaxy reveals details that would otherwise remain hidden. It shows the presence of numerous gaseous knots in which stars are forming at furious rates. The knots have sizes of around 700 light-years and are distributed over a region of about 15,000 light-years. In comparison, our galaxy, the Milky Way, is about 100,000 light-years across.

Despite its relatively small size, the distant galaxy is exceptionally bright. It outshines the Milky Way ten-fold due to the firestorm of starbirth within it. Among the young stars are many that are exceptionally massive and very luminous.

Gaseous winds blow from these star-forming knots outward into intergalactic space with speeds of nearly half a million miles per hour. Presumably, these flows are powered by the explosions of supernovae that go off at rates thousands of times greater than in today's more mature galaxies.

Conclusion

Astronomers draw this conclusion from these observations: We are seeing a small galaxy in its formative stage at a time when the universe was very young. Primordial gas collapsed to form the galaxy's early generations of stars and star clusters. The most massive of these stars raced through their evolution and exploded as supernovae. The explosions caused the observed outflow of gas, but they also compressed neighboring gas to form still more stars. Young galaxies like this one are believed to have collided and merged with others to eventually form the massive galaxies, like the Milky Way, that populate today's universe.

Garth Illingworth of the University of California, Santa Cruz, and one of the co-discoverers, summarizes the results as follows: "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. 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."

More Cool Stuff

We obtained the above images from press release 97-25 of the Space Telescope Science Institute (STScI):

http://oposite.stsci.edu/pubinfo/PR/97/25.html

To learn more about the HST and the W. M. Keck Observatory, go to:

http://oposite.stsci.edu/pubinfo/ and
http://www2.keck.hawaii.edu:3636/

For additional information on star and galaxy formation, go to our Observation of the Week Archive and click on "Stars, Galaxies, Universe":

http://observe.ivv.nasa.gov/nasa/ootw/1997/oarch_index.html

We have a Web article on the "Birth of Stars" in our Space Science pages:

http://observe.ivv.nasa.gov/nasa/space/space_index.shtml

NASA supports a number of educational Web sites that have excellent space science information:

"Eyes on the Sky, Feet on the Ground," a set of pages of the Web site "Using Science and the Internet as Everyday Classroom Tools" from the Smithsonian Astrophysical Observatory:

http://hea-www.harvard.edu/ECT/the_book/

The "Public Connection" Web site, an outreach project of Rice University and the Houston Museum of Natural Science:

http://space.rice.edu/hmns/connect.html

The "Science Information Infrastructure" project of the University of California at Berkeley:

http://www.cea.berkeley.edu/Education/SII/SEGway/

"Windows to the Universe," an innovative and engaging Web site about the Earth and space sciences from the University of Michigan:

http://www.windows.umich.edu/