Planetary Nebulae

Some of the most gorgeous, ghostly, and variable objects in the universe are planetary nebulae.  They are all formed in a similar process, as a low-mass star (like our Sun) sheds it’s outer layers of gas and dust, heating them to a glow as they disperse over hundreds of millions of years.  A few Billion years from now, the Sun will undergo the same major state change.  When this happens, perhaps other species in the far future will gaze upon it and marvel at its beauty.

One of the difficulties in studying a planetary nebula is measuring it’s distance from Earth.  But with a new elegant relation, a team of astronomers from the university of Hong Kong have found an accurate way to measure their distance, and along with it, other interesting properties like their size.

A collage showing 22 individual planetary nebulae artistically arranged in approximate order of physical size. The scale bar represents 4 light years. Credit: ESA/Hubble & NASA, ESO, Ivan Bojicic, David Frew, Quentin Parker

Lead author Dr. David Frew, from the University of Hong Kong, said: “For many decades, measuring distances to Galactic planetary nebulae has been a serious, almost intractable problem because of the extremely diverse nature of the nebulae themselves and their central stars. But finding those distances is crucial if we want to understand their true nature and physical properties.”

The new relation involves taking measurements of only the projected size of the object on the sky, it’s measured brightness, and an estimate of how much dimming it experiences from interstellar dust and gas between the nebula and Earth.  Once they determine how far away the object is, combining it with the apparent size of the object on the sky reveals it’s actual size in light years.  Calculations of the sizes of several planetary nebulae were done by the astronomers and used to produce the above image of the relative sizes of a sample of bright and beautiful objects.

“Our new scale is the first to accurately determine distances for the very faintest planetaries” said Dr Frew. “Since the largest nebulae are the most common, getting their distances right is a crucial step.”

 

 

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