APOD: NGC 2440: Cocoon of a New White Dwarf (2010 Feb 21)

[APOD Robot]

NGC 2440: Cocoon of a New White Dwarf

Explanation: Like a butterfly, a white dwarf star begins its life by casting off a cocoon that enclosed its former self. In this analogy, however, the Sun would be a caterpillar and the ejected shell of gas would become the prettiest of all! In the above cocoon, the planetary nebula designated NGC 2440, contains one of the hottest white dwarf stars known. The white dwarf can be seen as the bright dot near the photo's center. Our Sun will eventually become a white dwarf butterfly but not for another 5 billion years. The above false color image was post-processed by Forrest Hamilton.

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[neufer]

NGC 2440 is a planetary nebula situated in the Puppis constellation located about 4,000 light years from the Sun. It was discovered by William Herschel on March 4, 1790. He described it as "a beautiful planetary nebula of a considerable degree of brightness, not very well defined."

HD62166, with an estimated 0.6 solar mass and 0.028 solar radius,
has an exceptionally high surface temperature of about 200,000 kelvins.>>

<<A white dwarf is very hot when it is formed but since it has no source of energy, it will gradually radiate away its energy and cool down. This means that its radiation, which initially has a high color temperature, will lessen and redden with time. Over a very long time, a white dwarf will cool to temperatures at which it will no longer be visible, and become a cold black dwarf. However, since no white dwarf can be older than the age of the Universe (approximately 13.7 billion years), even the oldest white dwarfs still radiate at temperatures of a few thousand kelvins, and no black dwarfs are thought to exist yet.>>

λ_max (HD62166) ~ 145 Ångströms = 14.5 nm

<<Wien's displacement law provides the inverse relationship
between the wavelength of the peak of the emission of a black body
and its temperature when expressed as a function of wavelength

λ_max ~ [29,000,000 / T] Ångströms ~ [2,900,000 / T] nm ~ [2900 / T] microns

where T is the temperature of the blackbody in kelvins (K).>>

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Art Neuendorffer
"a beautiful asternaut of a considerable degree of brightness, not very well defined."

[neufer]

<<The star [HD62166] at the center of planetary nebula NGC 2440, is a bright white dwarf star's surface has been measured at greater than 200,000 degrees Celsius - more than 30 times hotter than that of our own Sun. The white dwarf's extreme heat makes it glow extraordinarily bright: intrinsically more than 250 times brighter than the Sun.>>

It is somewhat misleading to simply state that the white dwarf HD62166
is "intrinsically more than 250 times brighter than the Sun."

With an apparent magnitude of 18.9 and distance 1230 parsecs
the absolute magnitude of HD62166 is just 8.45 (versus 4.83 for Sol)
making the white dwarf HD62166 28 times fainter than the Sun in the visible.

However, with an apparent magnitude of 9.4
the absolute magnitude of the planetary nebula NGC 2440 is -1.05
making the planetary nebula 225 times brighter than the Sun in the visible
thanks to the powerful UV radiation of the white dwarf HD62166.

[biddie67]

In neufer's 8:15 AM post above, a Wiki article is referenced that states:

Over a very long time, a white dwarf will cool to temperatures at which it will no longer be visible, and become a cold black dwarf

Then after the graph, mention of a "black body" is made. I don't understand the connection between a cooling black dwarf that seems destined to be just like a future asteroid of some kind and a black body (according to my beginner's understanding of a black body) .....


On another side, the description under the APOD picture mentioned that "false color" was added to the photograph which really made it a beautiful art object but what did the photo look like before such processing? I'd also be interested in the original photo and why/what the technician/artist was attempting to emphasize ...

[RJN]

biddie67,

Thanks for your good questions. "Black body" is a technical term and doesn't necessarily mean the object appears black. The term means that the object doesn't reflect any light and glows only because is it hot. As the object cools, it glows less and less. Eventually it will appear black. A cooling white dwarf can be considered a "black body" in the sense of the technical term.

The false colors were chosen by a member or members of the Hubble Heritage Team, a group of astronomers who take old and archived Hubble images, find the raw photographs taken separately in different colors, and combine those images into one usually spectacular image. Now they can choose different images to combine, and use a Photoshop type program to make different colors more prominent. I believe the color processing on NGC 2440 was done by Forrest Hamilton, who is linked near the end of the APOD text. To find a different mix of colors, click the link "above cocoon" in the APOD text. Personally, I liked Forest's mix the best, and so I chose that one for this APOD. BTW, many times the word "above" in the APOD text is linked to the original image location on the web.

I hope this is a help! - RJN

[neufer]

In neufer's 8:15 AM post above, a Wiki article is referenced that states:

Over a very long time, a white dwarf will cool to temperatures at which it will no longer be visible, and become a cold black dwarf

Then after the graph, mention of a "black body" is made. I don't understand the connection between a cooling black dwarf that seems destined to be just like a future asteroid of some kind and a black body (according to my beginner's understanding of a black body) ......

A "black body" is simply an idealized opaque thermal radiator whose color is determined entirely by temperature.

A "white dwarf" is generally assumed to be an ~earth sized "black body" whose temperature is above ~20,000K.
A "black dwarf" is a hypothetical former white dwarf which has cooled to a temperature below ~2,000K.

Unfortunately, "red dwarfs" & "brown dwarfs" are ~solar sized "black bodies" that have nothing to do with the above dwarfs.

[biddie67]

Thanks folks!! Every time, I pull up a new page, I discover layers of relationships and complexities that seem so impossible to even exist. It's amazing to me how the human mind has struggled to define and understand things that seem so beyond us - much like a voting ballot might be to an ant ....

[bystander]

Unfortunately, "red dwarfs" & "brown dwarfs" are ~solar sized "black bodies" that have nothing to do with the above dwarfs.

While red dwarfs maybe ~solar sized, I thought brown dwarfs were closer in size to Jupiter and other high mass planets.

[neufer]

Unfortunately, "red dwarfs" & "brown dwarfs" are ~solar sized "black bodies" that have nothing to do with the above dwarfs.

While red dwarfs maybe ~solar sized, I thought brown dwarfs were closer in size to Jupiter and other high mass planets.

Indeed.

I was simply trying to explain as simply as I could that
red & brown dwarfs are fairly normal solar like objects
that are totally unrelated to white & black dwarfs
(without getting into that whole degenerate electron thing).

[Case]

Unfortunately, "red dwarfs" [...] have nothing to do with the above dwarfs.

Dave Lister, the last human, traveling on the space ship Red Dwarf: "We're on a mining ship, three million years into deep space. Can someone explain to me where the smeg I got this traffic cone from?"