nearby white dwarfs

en.wikipedia.org/wiki/White_dwarf has a nice overview of white dwarfs and what we think we know about them. -|Tom|-

The article on WDs says nothing as to why they orbit different types of stars. It only says they evolved from red giant stars. How can so many WDs be so close to the sun and not observed to be cooling over time? Did they all go SN at the same time? Would they cool off in a regular manner and then by measuring the amount of cool down calculate the time of the SN event?

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Jim</i>
<br />The article on WDs says nothing as to why they orbit different types of stars. It only says they evolved from red giant stars.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Most double stars have components that are unalike. You seem to think they should be similar.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">How can so many WDs be so close to the sun and not observed to be cooling over time?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Cooling? What are you referring to that could change significantly in just a century or two so we could observe it?

The fundamental problem here appears to be the idea that the local population has been around for very long. It hasn't. There is a pretty complete change in the local population every ten million years as stars move randomly about within the Galaxy. The only exception is a handful of stars in the Ursa Major group, of which the Sun may be a member co-moving with the rest.

Consider also that the lifetime of giant stars can be as short as a million years, or even less. Even the smaller giants are among the youngest stars in the Galaxy. So new white dwarfs are being created all the time all over the Galaxy. A few of these are always drifting into and out of the solar neighborhood. -|Tom|-

WDs orbit all kinds of stars but the WDs themselves are more or less all alike as far as the radiation from them goes. So, if they have been made throughout the 12by or whatever time span they should have cooled enough to see some difference in the radiation. I'm wondering if there is a way to determine if the radiation observed from WDs is always the same or not and how it may vary from WD to WD.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Jim</i>
<br />WDs orbit all kinds of stars but the WDs themselves are more or less all alike as far as the radiation from them goes. So, if they have been made throughout the 12by or whatever time span they should have cooled enough to see some difference in the radiation. I'm wondering if there is a way to determine if the radiation observed from WDs is always the same or not and how it may vary from WD to WD.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Theory indicates that cooling should occur, but only very slowly. I don't know of any data on this. But suppose we observed some range of temperature for different white dwarfs. What would that prove? -|Tom|-

Since WDs are radiating at a temperature of 25,000k or so they should cool over time and the amount of cooling should indicate age. At the temperature and size of WD objects they should radiate a lot of energy over a few billion years so older ones should be radiating at a lower temperature. This should prove weather or not the WD is older than the star it orbits as well as a few other points.