Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2003 August 1 
Posted on 07/31/2003 10:32:53 PM PDT by petuniasevan
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2003 August 1
Explanation: In this serene view, the moons of Earth along with the bright planet Mars shine above the city of Turku near the southwestern tip of Finland. Of course Earth's large natural satellite, the Moon, at a distance of 400,000 kilometers, is by far the brightest object in this sky. But growing brighter and closer by the hour, Mars appears as the impressively bright "star" at the right, about 64 million kilometers from Turku. Streaking across the twilight sky between the two celestial beacons, Earth's largest artificial moon, the International Space Station, orbits about 400 kilometers above the planet's surface. To capture the moment, amateur astronomer Petteri Kankaro used a digital camera and combined exposures beginning at 23:34 Universal Time on July 17th.
From Astronomynow:
Wind and reflections from supermassive black hole
CHANDRA X-RAY OBSERVATORY CENTER RELEASE
Posted: July 28, 2003
 NGC 1068. Credit: X-ray: NASA/CXC/MIT/UCSB/P.Ogle et al.; Optical: NASA/STScI/A.Capetti et al. |
The elongated shape of the gas cloud is thought to be due to the funneling effect of a torus, or doughnut-shaped cloud, of cool gas and dust that surrounds the black hole. The torus, which appears as the elongated white spot in the accompanying 3-color X-ray images, has a mass of about 5 million Suns. Radio observations indicate that the torus extends from within a few light years of the black hole out to about 300 light years.
 This illustration depicts a massive black hole at the center of a galaxy. Around it is a swirling disk of gas, which gradually pours down into the black hole. As the gas falls inward, it heats up and glows brightly, getting hotter and hotter the closer it is to the event horizon. Some of the gas is blown away from the disk like steam from a kettle. As this gas streams off the disk, the intense radiation generated by the very hot gas near the event horizon forces the escaping gas into a cone and accelerates it to speeds as high as a tenth the speed of light. Illustration: CXC/M.Weiss |
Observations with the spectrometers aboard Chandra enable scientists to estimate the composition, temperature and flow velocity of the gas. They show that the composition of the material in the wind is roughly similar to that of the Sun's atmosphere, except for a deficit of oxygen atoms, and that it has a temperature of about 100,000 degrees Celsius (180,000 degrees Fahrenheit). The average gas speed is about 1 million miles per hour.
These Chandra data on NGC 1068 are consistent with a picture where the observer is looking along the edge of a torus of cool gas and dust around a supermassive black hole. In this case we see the indirect effects of the black hole, but do not get a direct view. In contrast, an observer looking down into the hole of the torus would see a brilliant black hole source.
 An artist's conception shows a black hole surrounded by a disk of hot gas, and a large doughnut or torus of cooler gas and dust. The light blue ring on the back of the torus is due to the fluorescence of iron atoms excited by X-rays from the hot gas disk. Illustration: CXC/M.Weiss |
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