Using NASA's Hubble Space Telescope an international team of astronomers is uncovering intriguing new details about the most distant galaxy known, located more than ten billion light-years away.
Hubble reveals a surprising chain of luminous knots at the galaxy's core. "These knots could be giant star clusters forming. If that is so then each would contain about ten billion stars and be 1,500 light-years across," said Prof. George Miley of Leiden University, The Netherlands.
An alternative theory is that the knots are gas or dust clouds caught in a "searchlight" beam of energy from a massive black hole hidden at the galaxy's core.
The primordial galaxy, called 4C41.17, existed during the infancy of the universe. The galaxy's great distance from earth means that it formed less than two billion years after the Big Bang, which marked the beginning of the observable universe. Most galaxies might have formed during this early epoch.
The new picture of 4C41.17 taken with the Wide Field and Planetary Camera on the Hubble Telescope resolves details ten times better than previous photographs taken with ground-based telescopes. This allows astronomers to study the center of the galaxy with unprecedented clarity.
"A surprising result is the extreme dumpiness of the visible emission, suggesting that the inner region of this primeval galaxy is highly disturbed," said Miley.
The observations were carried out by Miley and co-investigators Kenneth Chambers of the University of Hawaii, Wil van Breugel of Lawrence Livermore National Laboratories of the University of California, and Duccio Macchetto of the Space Telescope Science Institute, Baltimore and the European Space Agency. The results will be published in the December 20th issue of Astrophysical Journal Letters.
4C41.17 is one of several distant radio-emitting galaxies, discovered by members of the team during the past few years. The team's search and detection strategy is based on the enormous power and special character of the radio emission from such distant galaxies.
In 4C41.17 a massive black hole rotating at the galaxy's core is commonly thought to be the "engine" which produces twin jets of high-speed particles. The energy from the jets would be the source of the radio emissions.
"The Hubble pictures appear remarkably similar to radio images produced by the Very Large Array of the National Radio Astronomy Observatory in New Mexico," said Miley. It has been known for some years that radio jets interact vigorously with the outer regions of distant radio galaxies. However, the new results show for the first time a close alignment between the optical and radio features in the central regions of such galaxies.
One possible explanation for this alignment between the optical and radio emission is that the high velocity jets of particles which produce the radio emission also compress gas and dust along their paths, triggering new star formation. The new stars would then preferentially be born along the jets' paths, creating the elongated optical appearance seen in 4C41.17.
Another possibility is that the optical emission is not due to stars, but is produced by light scattering off clouds of gas or dust. The clumps would be illuminated by light from the accretion disk around an active black hole embedded deep in the galaxy's core. This active galactic nucleus, or quasar, would be hidden from our view by a thick dust shroud which allows light to escape only along the radio axis.
Hubble can help discriminate between these possibilities by studying further the colors and other properties of these and similar objects. After the scheduled Space Shuttle servicing mission for Hubble in late 1993, astronomers will be able to take much deeper pictures in a shorter time.
Space Telescope can then be used to carry out detailed studies of many galaxies at distances comparable to 4C41.17. "More than 50 are now known," said Miley. "Observing them with the renewed Hubble would provide us with an important new window through which we can glimpse the early history of our universe."