RAS: "Planetary Nebulae" Get More Meaningful Physical Presence

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RAS: "Planetary Nebulae" Get More Meaningful Physical Presence

Post by bystander » Sat Nov 21, 2015 5:41 pm

Ghostly and Beautiful: "Planetary Nebulae" Get More Meaningful Physical Presence
Royal Astronomical Society | 2015 Nov 20
[c][attachment=0]nebulae_montage.jpg[/attachment][/c][hr][/hr]
A way of estimating more accurate distances to the thousands of so-called planetary nebulae dispersed across our galaxy has been announced by a team of three astronomers based at the University of Hong Kong: Dr. David Frew, Prof. Quentin Parker, and Dr. Ivan Bojicic. ...

Despite their name, planetary nebulae have nothing to do with planets. They were described as such by early astronomers whose telescopes showed them as glowing disc-like objects.

We now know that planetary nebulae are actually the final stage of activity of stars like our Sun. When they reach the end of their lives, these stars eject most of their atmosphere into space, leaving behind a hot dense core. Light from this core causes the expanding cloud of gas to glow in different colors as it slowly grows, fading away over tens of thousands of years.

There are thousands of planetary nebulae in our galaxy alone, and they provide targets for professional and amateur astronomers alike, with the latter often taking spectacular images of these beautiful objects. But despite intense study, scientists have struggled to measure one of their key properties -- their distance. ...

The solution presented by the astronomers is both simple and elegant. Their method requires only an estimate of the dimming toward the object (caused by intervening interstellar gas and dust), the projected size of the object on the sky (taken from the latest high resolution surveys) and a measurement of how bright the object is (as obtained from the best modern imaging). ...

The Hα surface brightness-radius relation: a robust statistical distance
indicator for planetary nebulae
- D.J. Frew, Q.A. Parker, I.S. Bojicic
Attachments
A collage showing 22 individual planetary nebulae artistically arranged in <br />approximate order of physical size. Each nebula's size is calculated from <br />the authors' new distance scale, which is applicable to all nebulae across <br />all shapes, sizes and brightnesses. The very largest planetary nebula <br />currently known is nearly 20 light years in diameter, and would cover the <br />entire image at this scale. <br />Credit: ESA/Hubble &amp; NASA, ESO, Ivan Bojicic, David Frew, Quentin Parker
A collage showing 22 individual planetary nebulae artistically arranged in
approximate order of physical size. Each nebula's size is calculated from
the authors' new distance scale, which is applicable to all nebulae across
all shapes, sizes and brightnesses. The very largest planetary nebula
currently known is nearly 20 light years in diameter, and would cover the
entire image at this scale.
Credit: ESA/Hubble & NASA, ESO, Ivan Bojicic, David Frew, Quentin Parker
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