New images of the mysterious superstar Eta Carinae by NASA's Chandra X-ray Observatory reveal a surprising hot inner core -- creating more questions than answers for astronomers.
The new X-ray observation shows three distinct structures: an outer, horseshoe shaped ring about two light-years in diameter, a hot inner core about 3 light-months in diameter, and a hot central source less than a light-month in diameter which may contain the superstar. In one month, light travels a distance of approximately 489 billion miles (about 788 billion kilometers).
All three structures are thought to represent shock waves produced by matter rushing away from the superstar at supersonic speeds. The temperature of the shock-heated gas ranges from 60 million degrees Kelvin in the central regions to 3 million degrees K on the outer structure.
An earlier image of Eta Carinae by the Hubble Space Telescope revealed two spectacular bubbles of gas expanding in opposite directions away from a central bright region at speeds in excess of a million miles per hour. The inner region visible in the Chandra image has never been resolved before, and appears to be associated with a central disk of high velocity gas rushing out at much higher speeds perpendicular to the bipolar optical nebula.
"It is not what I expected," said Chandra researcher Dr. Fred Seward of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "I expected to see a strong point source with a little diffuse emission cloud around it. Instead, we see just the opposite -- a bright cloud of diffuse emission, and much less radiation from the center."
"The Chandra image poses a problem for one of the currently most favored theories for the X-ray emission from the central region of Eta Carinae," agreed Professor Kris Davidson of the University of Minnesota in Minneapolis. "Namely that it is due to the collision of shells of material thrown off by two stars circling one another. In such a scenario, you would expect to see a much stronger point source."
Eta Carinae is one of the most enigmatic and intriguing objects in our galaxy. Between 1837 and 1856 it increased dramatically in brightness to become the most prominent star in the sky except for Sirius, even though it is 7,500 light years away, more than 80 times the distance to Sirius. This "Great Eruption," as it is called, had an energy comparable to a supernova, yet did not destroy the star, which faded to become a dim star, invisible to the naked eye. Since 1940, Eta Carinae has begun to brighten again, becoming visible to the naked eye.
Modern day observations of Eta Carinae have shown it to be the most luminous object known in our galaxy. It radiates at the rate of several million times that of the Sun. Most of the radiation is at infrared wavelengths, from dust in the bipolar nebula. Astronomers still do not know what lies at the heart of Eta Carinae. Most believe that it is powered by an extremely massive star that may be a hundred times as massive as the Sun. Such stars produce intense amounts of radiation that cause violent instabilities before they explode as a supernova.
The Chandra X-ray image gives a glimpse deep into the nebula where the fastest material being thrown off by Eta Carinae is found. The outer ring provides evidence of another large explosion that occurred over a thousand years ago. Further Chandra observations of Eta Carinae are planned for the near future and should give astronomers deeper insight into this cryptic colossus.
To follow Chandra's progress, visit the Chandra site at:
The Eta Carinae X- ray image will be available on NASA Television at noon, 3 p.m., 6 p.m., 9 p.m. and midnight EDT on Friday, Oct. 8. NASA Television is broadcast on GE-2, transponder 9C at 85 degrees West longitude, with vertical polarization. Frequency is 3880.0 megahertz, with audio on 6.8 megahertz.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program. TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass.
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