"This is a giant leap backwards in our understanding of quasars," says Professor John Bahcall of the Institute of Advanced Study at Princeton.
Since their discovery in 1963, quasars have been enigmatic because they emit prodigious amounts of energy from a very compact source. The most widely accepted model is that a quasar is powered by a supermassive black hole in the core of a more or less normal galaxy. However, confirming this model has been difficult because a quasar is so bright it drowns out the light from the stars in the suspected host galaxy.
Using the Wide Field Planetary Camera/2, Bahcall observed fourteen of the brightest and nearest quasars, assuming that the Space Telescope's resolution and sensitivity would at last reveal the host galaxies suggested by previous ground-based observations.
"We were astonished when images of eight quasars did not reveal the bright host galaxies, as we expected based on simulations," says Bahcall, who conducted the observations with Donald Schneider, Pennsylvania State University, and Sofia Kirhakos, also of the Institute for Advanced Study. However, moderately bright host galaxies were identified in three other quasars observed.
Donald Schneider emphasizes: "We are struggling to understand how our images fit into the general picture of quasar creation and evolution. This is the most enigmatic data I have ever analyzed, and it is much too early to know what the final conclusions will be."
Even more puzzling, Hubble images reveal that these apparently naked quasars have distinct companion galaxies that are so close that they will merge with the quasars in no more than ten million years.
One pair in particular Bahcall calls the "smoking gun" because it reveals a galaxy that has been distorted by the gravitational pull of the quasar. Bahcall concludes, "this is clear evidence for interactions between this quasar and its nearby companion galaxy." This would mean that the quasars seen with a host galaxy have been caught in the act of merging with their companion.
Bahcall and his colleagues plan to extend his survey to other quasars. Their observations to date provide a new challenge for theorists since no current models predict the complex quasar interaction unveiled by Hubble. This Hubble Space Telescope image shows evidence for a merger between a quasar and a companion galaxy. This surprising result might require theorists to rethink their explanations for the nature of quasars, the most energetic objects in the universe.
The bright central object is the quasar itself, located several billion light-years away. The two wisps on the of the bright central object are remnants of a bright galaxy that have been disrupted by the mutual gravitational attraction between the quasar and the companion galaxy. This provides clear evidence for a merger between the two objects.
The latest HST images are available on the World Wide Web at STSci.
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