Among its array of revelations in the past 12 months, news about black
holes pulled in most of the headlines with four of the top five stories
from Chandra during its fourth year in operation. But it was the
venerable Crab Nebula, with the spectacular Chandra/Hubble movie
production of its amazing pulsar and dazzling tornado of high-energy
particles and magnetic fields, that captured first place as our most popular image.
Attracting the top spot in media coverage was the galaxy NGC 6240, which was discovered to have not one, but two supermassive black holes orbiting each other in the nucleus of the galaxy. As the first definite identification of a binary supermassive black hole system, this discovery stimulated a great deal of scientific interest, and a flood of questions to our web site. People wanted to know when the two black holes would merge (a few hundred million years), whether the galaxy would survive (yes), whether we would survive (yes), and if the merger had happened already, given that NGC 6240 is 400 million light years away (probably).
The supermassive black hole Sagittarius A* (Sgr A*) located at the center of our galaxy makes a repeat appearance near the top of our list in both scientific importance and popularity. Since it is the nearest supermassive black hole, it seems a good bet to remain high on everyone's list in years to come as astronomers seek a much better understanding of how supermassive black holes grow and how they influence the evolution of the galaxies in which they reside.
Another black hole story that could make big news in the future was first reported this year. By combing the data from the Chandra Deep Field North and Chandra Deep Field South images, astronomers made a high-energy "core sample" of the early universe. In addition to hundreds of supermassive black holes, they found seven mysterious sources that were not detected by the Hubble Space Telescope. These X-ray sources are candidates for the most distant supermassive black holes ever observed.
Rounding out the top five stories this past year was a series of Chandra images of oppositely directed jets from XTE J1550, a stellar black hole in our galaxy. These observations made at intervals over a four-year period allowed scientists to trace the evolution of large-scale X-ray jets for the first time. Such jets are thought to be one of the primary ways that black holes interact with their environment.
Jets figured in one of the most beautiful images of the year, which was also one of the most popular with the press and the public. The composite X-ray, radio and optical image of the galaxy Centaurus A presents a stunning tableau of a galaxy in turmoil. A broad band of dust and cold gas is bisected at an angle by opposing jets of high-energy particles blasting away from the supermassive black hole in its nucleus. Two large arcs of multimillion degree gas indicate that a titanic explosion rocked the galaxy about ten million years ago.
X-rays produced by fluorescent radiation from oxygen atoms gave astronomers a unique look at the sparse upper atmosphere of Mars, about 45 kilometers (45 miles) above its surface, and provided evidence for a faint halo of X-rays that extends out to 7,000 kilometers above the surface.
The image of M83 revealed an ethereal beauty, with a graceful spiral of neutron stars and black holes around a blazing, starburst heart of multimillion degree gas.
A fascination with the macabre no doubt accounted for some of the popularity of the "Black Widow" pulsar, a neutron star that is destroying its stellar companion. The science was also intriguing, as the image provided the first direct evidence of an elongated cocoon of high-energy particles around this old pulsar and that is speeding through interstellar space.
Finally, Chandra's image of Tycho's supernova remnant reveals in elaborate detail the turbulent debris created by the stellar catastrophe that was observed by the Danish astronomer Tycho Brahe in the year 1572. We have come a long way from that observation --made before the invention of the telescope-- which provided the first evidence that stars are not eternal.
Top 10 Chandra Images 2003 (requires flash)
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Updated: March 27, 2008
