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Pedants' Corner - How much does a white dwarf weigh? [Dec. 14th, 2005|04:22 pm]
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Hubble weighs closest white dwarf says the BBC. Only it didn't. As the first sentence of the article says, it was used to measure the mass.

As weight measures the force of attraction between two objects due to gravity then, especially when talking about space (where the acceleration due to gravity varies), it is not interchangeable.

Update: perhaps unsurprisingly, they've now corrected it.
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Comments:
[User Picture]From: mysterycult
2005-12-14 07:07 pm (UTC)

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Whilst justifiable, I can't help but feel this is the oldest of olde pedantrye. Next you'll be chronicling sign's in grocers shop's where the apostrophes' are in the wrong place's.
From: amoebic_vodka
2005-12-14 10:13 pm (UTC)

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True in general, but we think this is particularly bad as the article talks about gravity quite a lot (and the only use of weight to mean mass occurs in the title). We'd like to think journalists should at least have a vague clue what they're writing about.
[User Picture]From: mysterycult
2005-12-14 10:38 pm (UTC)

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But the subeditors who write the article titles never know what they're writing about. They're selected for their ability to make bad puns.
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From: amoebic_vodka
2005-12-15 10:32 am (UTC)

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We're not so sure. What they measured (indirectly) was the strength of the star's gravitational field. That's not its weight.

The press release is here and goes into more detail about how they did it:

Astronomers Use Hubble to 'Weigh' Dog Star's Companion
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From: amoebic_vodka
2005-12-15 01:56 pm (UTC)

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Mysteriously, we seem to have full text access to the paper

Hubble Space Telescope spectroscopy of the Balmer lines in Sirius B (the abstract)

They used another method to calculate the mass by measuring the gravitational field strength (g) at the surface too (again using the Hubble data). This still doesn't say what the weight of the star is.
From: (Anonymous)
2005-12-15 03:35 pm (UTC)

puns law

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Surely they can't measure mass this way, not Siriusly at least...
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From: amoebic_vodka
2005-12-16 08:42 am (UTC)

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You might be right. However we still don't think they even know what the weight of the star is. Surely with something so dense, the gravitational field strength of the star itself would change sharply between the star's surface and centre. Then it is a binary system with Sirius A and that star also will have a gravitational field. We suspect that both those things would make any measurement of the force of gravity *on* the star impossible.

If they did any weighing it was of the light rather than the star (if that makes sense). So it's still not weighing the star...

...well we did say this was pedants' corner after all.