Talk:BPM 37093

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Just can't resist... so when singing about this object, one should sing "Lucy in the sky's a diamond." *grins* - UtherSRG 20:44, 19 Jul 2004 (UTC)

[edit] Why not a diamond?

The article claims that the density means that the star can't be a diamond. Does anyone have a reference for that claim? Carbon doesn't have very many crystalline structures, after all, and diamond is much denser than graphite... --Andrew 03:36, Apr 13, 2005 (UTC)

Diamond isn't much more dense (3.5 vs. 2.3 g/cm^3). In both cases, ordinary covalent bonds are present. In a white dwarf star, the electrons stack up in degenerate shells (as you'd find in an atom, or somewhat like you'd find in a piece of metal), but the nuclei are free to move around. For a hot white dwarf, this gives you an ordinary gas of carbon nuclei inside the (arguably crystalline) degenerate gas of electrons. For a white dwarf that cools sufficiently, you'd get the nuclei arranging themselves in a close-pack lattice to maintain as large a separation as possible at a given density. Many terrestrial materials have this lattice structure, but diamond isn't one of them (covalently bonded crystals have a small number of neighbours per atom). At the very surface of the star, you might get something resembling terrestrial diamond, but that would only be a very thin crust (high surface gravity means pressure increases quickly enough with depth to give you close-packing and to force electrons to be shared as opposed to stuck in covalent bonds or atoms' core shells). --Christopher Thomas 04:44, 28 June 2006 (UTC)

[edit] Not a diamond?

Every quote from the astronomers refers to it as a diamond; the "five tonne" comment comes only from the BBC reporter. Perhaps that was just a flub on her part, much like CNN's FTL velocity for the Space Shuttle Columbia?

[edit] Simple calculations

Density of diamond = 3.51 g/cm³ [1] [2] (or any basic mineralogy text).

Using the data from the Harvard press release and some simple calculations, the density of the carbon in the white dwarf "ash" works out to 2.7x10¹⁴ g/cm³. Now, is 3.51 equal to 270,000,000,000,000? Don't trust my calculations, grab a calculator and do your own (I may have goofed :-).

Astronomers do like to have fun and embellish the language a bit to grab the attention of reporters and the general public. After all - a diamond in the sky is a lot more newsworthy? or attention getting than super dense stellar carbon ash. I note the press release also states that the object "rings like a gigantic gong" - listen and you can hear it now from 50 light years away (and I just thought it was tinnitus).

Er, it does in fact ring; that's how they measured its properties. --Andrew 17:09, May 16, 2005 (UTC)

The BBC reporter didn't "flub" as much as some gullible wikipedians are "flubbing", this is absurd. Vsmith 03:52, 15 May 2005 (UTC)

Diamonds, like most solids, are compressible; given high enough pressure (which is the case here) the denisty will increase. Really the question is about the crystal structure of the carbon - is it bonded like a diamond, like graphite, or like nothing on earth? Because diamond is the densest at atmospheric pressure, it seems likely that a diamond crystal structure is the densest and hence the most stable at these enormous pressures. But I have no idea.

It may be the case that there is a qualitative difference between the degenerate matter making up a white dwarf and ordinary solid diamond, but I don't know enough condensed matter physics to understand. --Andrew 16:40, May 16, 2005 (UTC)

In fact, according to [3], written by Travis Metcalfe, the leader of the original team, the discovery is not that the star is mad of carbon, but that it is crystalline carbon. Now, of the possible crystal structures, diamond is the densest, and this is how the astronomers described it, so I'm inclined to believe that it really is diamond. Not much like ordinary diamond, of course, being incredibly dense, but it is specifically solid crystalline carbon. --Andrew 17:09, May 16, 2005 (UTC)