Hubble sees the glowing eye of a planetary nebula
SPACE TELESCOPE SCIENCE INSTITUTE RELEASE
Posted: April 6, 2000
Astronomers using NASA's Hubble Space Telescope have obtained images of the strikingly unusual planetary nebula, NGC 6751. Glowing in the constellation Aquila like a giant eye, the nebula is a cloud of gas ejected several thousand years ago from the hot star visible in its center.
The Hubble observations were obtained in 1998 with the Wide Field Planetary Camera 2 (WFPC2) by a team of astronomers led by Arsen Hajian of the U.S. Naval Observatory in Washington, DC. The Hubble Heritage team, working at the Space Telescope Science Institute in Baltimore, has prepared this color rendition by combining the Hajian team's WFPC2 images taken through three different color filters that isolate nebular gases of different temperatures.
The nebula shows several remarkable and poorly understood features. Blue regions mark the hottest glowing gas, which forms a roughly circular ring around the central stellar remnant. Orange and red show the locations of cooler gas. The cool gas tends to lie in long streamers pointing away from the central star, and in a surrounding, tattered-looking ring at the outer edge of the nebula. The origin of these cooler clouds within the nebula is still uncertain, but the streamers are clear evidence that their shapes are affected by radiation and stellar winds from the hot star at the center. The star's surface temperature is estimated at a scorching 140,000 degrees Celsius (250,000 degrees Fahrenheit).
Hajian and his team are scheduled to reobserve NGC 6751 with Hubble's WFPC2 in 2001. Due to the expansion of the nebula, at a speed of about 40 kilometers per second (25 miles per second), the high resolution of Hubble's camera will reveal the slight increase in the size of the nebula since 1998. This measurement will allow the astronomers to calculate an accurate distance to NGC 6751. In the meantime, current estimates are that NGC 6751 is roughly 6,500 light-years from Earth. The nebula's diameter is 0.8 light-years, some 600 times the diameter of our own solar system.
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