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.
2002 August 30 
Posted on 08/29/2002 9:16:35 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.
2002 August 30
Explanation: It's easy to get lost following the intricate filaments in this stunningly detailed image of faint supernova remnant Simeis 147. Seen towards the constellation Taurus it covers nearly 3 degrees (6 full moons) on the sky corresponding to a width of 150 light-years at the stellar debris cloud's estimated distance of 3,000 light-years. On three separate nights in December 2001 and January 2002 astronomer Steve Mandel accumulated a total of over eight hours of exposure time to compose this image. He used an astronomical CCD camera, telephoto lens, and his specially designed adapter to allow such wide-field digital imaging. He also used a narrow H-alpha filter to transmit only the the light from recombining hydrogen atoms in the expanding nebulosity, defining the regions of shocked, glowing gas. This supernova remnant has an apparent age of about 100,000 years (light from the original explosion first reached Earth 100,000 years ago) but it is not the only aftermath of the massive stellar explosion. The cosmic catastrophe also left behind a spinning neutron star or pulsar, all that remains of the star's dense core.
The material thrown out by such stellar catastrophes is full of heavy elements needed for planet building and life itself.
It's the only way these elements can be accessed. Otherwise they would remain locked in the cores of stars.
Get on the 
list!
Happy Labor Day (Celebrate Work by Goofing Off Day) weekend!
There's that hydrogen alpha band filter again. Very special construction, 7 layers of glass, the last very, very thin and difficult to make.
This image is the kind of astronomy we like. Forget those big NASA orbiting telescopes, forget those monstrous ground-based compensating optics constructs. This is the kind of thing amateurs can do, if they are really dedicated.
When a supernova occurs, is the rate of expansion of the remaining ‘star stuff’ constant and dependent on the force of the initial explosion?
In other words, in the supernova pictured above, was the width of the debris equal to only 75 light years 50,000 years ago? And, will the width of the debris equal 300 light years, 100,000 years from now?
It would seem that if there is no gravitational pull (other stars) to slow it down, the debris will expand at a constant rate. No?
Have a good holiday.
Actually, the debris will sweep up gas and dust as it expands through nearby space and the energy that is released by collision and friction (think inertia) causes the "shock wave" effect that makes the above image glow in the light of ionized hydrogen. Thus, the supernova debris is slowed down slightly every time it contacts a gas molecule or dust mote.
The rate of deceleration will depend on how dense the gas and dust are in its path. As the debris passes near to other stars, it will be greatly affected and its appearance greatly altered. And when a bow shock front gathers enough mass, it can begin to affect its own shape as its gravity pulls it in on itself.
Now for the worm in the apple: the supernova left a pulsar behind. It produces a strong "pulsar wind" which it deposits into the surrounding medium, accelerating the debris outward as the pulsar loses angular momentum ("spins down"). So supernova shells can be difficult to "date" unless recent enough to have been recorded in human culture.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.