View Full Version : Discussion: White Dwarf Theories Get More Proof

2005-Jan-12, 06:44 PM
SUMMARY: New observations using NASA's Far Ultraviolet Spectroscopic Explorer (FUSE) satellite have given astronomers evidence that their assumptions and calculations about white dwarf stars are correct. FUSE made detailed observations of Sirius B, which is 10,000 times dimmer than its companion Sirius A (the brightest star in the sky). You can only measure the mass of a star in a binary system like this; you can observe the two stars' orbit, get the period, and then find the sum of the two star masses. These new observations helped astronomers determine Sirius B's size and mass within 1%.

View full article (http://www.universetoday.com/am/publish/white_dwarf_theory.html)

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2005-Jan-12, 07:12 PM
So many stories are about some new spectacular thing being discovered, but it is nice to see stories like this which basically show how the new equipment is confirming and refining details we were already pretty confident of.

2005-Jan-12, 07:30 PM
There is an arxiv version of this story which furnishes the actual numbers (I didn't save the URL). To the best of my recollection, the mass was fixed at 1.05 sols plus-or-minus 1%, the temperature was established within 150 Kelvin degrees, and the radius was established within 7%. Since these quantities (as well as density gradient) are interrelated, the real impact of the study was to provide a data point on the high-mass end of the curve. Previous studies centered on masses of .7 sols or so, and most were of single stars, leaving an uncertainty in the mass determination. S

2005-Jan-13, 01:55 PM
For me is very important to know (in percenta) how strong is e.magnetic field of Sirius B - comparable with gravity field of this white dwarf star.
Are there - enywhere such data, or calculations, graphs...?

2005-Jan-13, 02:28 PM
Originally posted by Guest@Jan 13 2005, 01:55 PM
For me is very important to know (in percenta) how strong is e.magnetic field of Sirius B - comparable with gravity field of this white dwarf star.
That's an interesting question. I'd have thought that a quick Google search would have turned up an answer, but it pops up a list with vague results including a lot of spiritual sites. Hmmm.

Just as an educated guess, I'd say it has a surface magnetic field of about 100,000 to 1,000,000 gauss [See This Table (http://www.astronomycafe.net/qadir/ask/a11654.html)]. I'm sure that somewhere there are specific numbers based on observations of this specific star.

Concerning whether this is comparable to it's gravity, I'm not sure how you'd measure it. If you had a hunk of something ferromagnetic [like Iron], would the force of gravity on the Iron be stronger than the magnetic attraction right at the surface of the star? Alterenatively, If you had a couple solar masses of Hydrogen and Helium fifty AU away, would the magnetic force be similar to the gravity? In the first case, I don't know, but suspect gravity is stronger. In the second case, there is no contest. Gravity is the only meaningful force holding Sirius A and Sirius B together.