This Hubble Space Telescope image (right) reveals the faint host galaxy that a bright quasar dwells within. The wealth of new detail in this picture helps solve a three-decade old mystery about the true nature of quasars, the most distant and energetic objects in the universe.
The HST image shows clearly that the quasar, called 1229+204, lies in the core of a galaxy that has a common shape consisting of two spiral arms of stars connected by a bar-like feature. The host galaxy is in a spectacular collision with a dwarf galaxy. The collision apparently fuels the quasar "engine" at the galaxy center - presumably a massive black hole - and also triggers many sites of new star-formation.
The image is one of a pair of relatively nearby quasars that were selected as early targets to test the resolution and dynamic range of HST's newly-installed Wide Field and Planetary Camera, which contains special optics to correct for a flaw in Hubble's primary mirror. The observations were made by Dr. John Hutchings of Dominion Astrophysical Observatory in Victoria, British Columbia. "The project was impossible from ground-based telescopes," says Dr. Hutchings, who has been researching quasars for many years. " The sharpness of the Hubble pictures is leading to major new discoveries almost anywhere you point it in the sky."
Quasars are the most distant objects in the universe, and so are among the earliest objects known to have formed in the young universe, more than 12 billion years ago. The most widely accepted notion is that quasars are in galaxies with active, supermassive black holes at their centers. However, because of their enormous distance, the `host' galaxies appear very small and faint, and are very hard to see against the much brighter quasar light at the center. Though a quasar might no be much larger than our solar system it releases as much energy as billions of stars.
Though a previous ground based observation using the Canada-France-Hawaii Telescope (at 0.5 arcsec resolution) first identified the barred spiral galaxy in 1229+204, Hubble shows clearly the galaxy's structure and reveals details of the collision.
Hubble reveals that an extended blue feature on one side of the galaxy is really a string of knots, which are probably massive young star clusters. The star clusters were most likely formed as a result of a collision between the host galaxy and a small gas-rich companion. HST also reveals shell-like structures along the bar that might be produced by gravitational tidal resonance forces between the spiral and its companion.
Credit: Dr. John Hutchings, Dominion Astrophysical Observatory, NASA