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White Dwarf, 12 Billion Years Old, Found Only 100LY Away

by Dotini
Tags: 100ly, billion, dwarf, white
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Dotini
#1
Apr13-12, 08:38 AM
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What a wonderful coincidence to find such an old star so close by!

http://phys.org/news/2012-04-astrono...arf-stars.html

Respectfully submitted,
Steve
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Chronos
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Apr13-12, 01:01 PM
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Here is the arxiv version http://arxiv.org/abs/1204.2570
Drakkith
#3
Apr13-12, 04:28 PM
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Nice! Thanks guys!

Radrook
#4
Apr14-12, 09:06 AM
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White Dwarf, 12 Billion Years Old, Found Only 100LY Away

Close by? Strange!
Dotini
#5
Apr17-12, 06:25 PM
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Quote Quote by Radrook View Post
Close by? Strange!
Why strange? Is that because the galaxy is ~100,000 LY in diameter, and 100 seems strangely small? As I understand it, our galaxy is peppered with white dwarfs.

Amusingly, NASA is thinking that a newly discovered galactic structure of 50,000 LY, the FERMI bubble, has arisen in only a few million years. http://www.nasa.gov/mission_pages/GL...structure.html

Does that seem odd, too?

Respectfully submitted,
Steve
DaveC426913
#6
Apr17-12, 06:36 PM
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Take that, fundamentalists!
DaveC426913
#7
Apr17-12, 06:39 PM
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We found its distance by measuring a tiny wiggle in its path caused by the Earth's motion...
"Your planet Earth is soooo fat (how fat is it?) - it causes a wiggle in SDSS J110217, 48+411315.4's motion! BOOyah!"

[ EDIT ] That is really sloppy journalism.

It sounds like they were saying "Earth's movement caused a wobble in the star's path". Well, that actually is what they said.

What they surely meant was "Earth's movement (around the sun) causes a parallax, by which we can observe how far away the star is". Which is a completely different thing.
Chronos
#8
Apr18-12, 01:03 AM
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Journalists are victimized by scientists who feed them just enough information to overload their simple, disordered neural networks.
TheTechNoir
#9
Apr18-12, 01:39 AM
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Quote Quote by Chronos View Post
Journalists are victimized by scientists who feed them just enough information to overload their simple, disordered neural networks.
Journalist: Scientists are overloading journalists with high levels of entropy! Or something like that.
TheTechNoir
#10
Apr18-12, 01:39 AM
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Quote Quote by Chronos View Post
Journalists are victimized by scientists who feed them just enough information to overload their simple, disordered neural networks.
Journalist: Scientists are overloading journalists with high levels of entropy! Or something like that. Physics makes it very difficult for us to reverse this and provide the world with low entropy articles about cosmology.
Kaldanis
#11
Apr18-12, 04:10 AM
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Obvious, stupid question time!

The article says the white dwarf was probably formed from a star similar to our sun. Our sun is about 4.6 billion years old and is expected to become a white dwarf too in another 5 billion years. So let's say it takes ~10 billion years to become a white dwarf. How can the white dwarf be 12 billion years old if the universe is only estimated to be 13.8 billion years old?

Unless... it means the star has existed for 12 billion years over its entire life?
Drakkith
#12
Apr18-12, 04:57 AM
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Quote Quote by Kaldanis View Post
Obvious, stupid question time!

The article says the white dwarf was probably formed from a star similar to our sun. Our sun is about 4.6 billion years old and is expected to become a white dwarf too in another 5 billion years. So let's say it takes ~10 billion years to become a white dwarf. How can the white dwarf be 12 billion years old if the universe is only estimated to be 13.8 billion years old?

Unless... it means the star has existed for 12 billion years over its entire life?
From the paper:
The initial-to-final
mass relation for WDs indicate that the progenitor of J1102
was a 1.8-2.2 M⊙ star (CatalŽan et al. 2008; Kalirai et al.
2009; Williams et al. 2009) with a main-sequence lifetime
of 0.6-1.1 Gyr (Marigo et al. 2008). Hence the total age of
this object is 10.6-11.1 Gyr. Similary, WD0346 is a 3650
K, 0.77 M⊙ star with a WD cooling age of 11.2+0.3
−1.6 Gyr.
The progenitor star was a 3.1-3.3 M⊙ main-sequence star
with a main-sequence lifetime of 240-270 Myr (Marigo et al.
2008).
J1102 only burned Hydrogen in it's core for about 2 billion years thanks to it's greater mass compared to the Sun (2x more). It formed a white dwarf soon after Hydrogen fusion ceased and has been cooling ever since.

WD0346 was even more massive, at around 3 solar masses, and burned through its hydrogen in about 250 million years, formed a white dwarf, and has been cooling since.
Kaldanis
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Apr18-12, 05:01 AM
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Thank you Drakkith :)
Ken G
#14
Apr18-12, 05:04 PM
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"We found its distance by measuring a tiny wiggle in its path caused by the Earth's motion... "

Although the statement is sure to confuse readers, there isn't necessarily anything wrong with saying the Earth's motion "caused" a wiggle in the star's motion, as long as one recognizes that all motion is relative, so any "wiggle" is relative also. It's merely an issue of what it is relative to. We might take the Copernican stance that motion of a star relative to a galaxy is "more absolute", in some sense, than motion relative to Earth, but the most empirically demonstrable stance is simply that motion itself requires the identification of an observer to say that the motion is there in the first place, and in that sense is "caused" by that relationship (true causality has no really solid foundation in physics). That would seem the most closely adhering to general relativity, but this article is never going to be used to teach general relativity, so readers will indeed get the wrong impression from that statement.
DaveC426913
#15
Apr18-12, 05:50 PM
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Quote Quote by Ken G View Post
Although the statement is sure to confuse readers, there isn't necessarily anything wrong with saying the Earth's motion "caused" a wiggle in the star's motion, as long as one recognizes that all motion is relative, so any "wiggle" is relative also.
My concern was more the implication that there was a gravitational effect. When I read it, is sounds like they're saying that Earth's mass actually made the star move.

We know it's preposterous, but many readers won't.
Ken G
#16
Apr19-12, 04:40 PM
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But in a sense, it is a "gravitational" affect in the larger sense of general relativity, where fictitious forces are treated on a similar footing as "real" forces which stem from the stress-energy tensor. But I know what you mean, it's not an effect related to the Earth's mass or anything like that, and the words are likely to be interpreted as if the Earth had some kind of special connection to the star, which can lead to pseudoscientific thinking about 2012 and who knows what else. I was just pointing out how slippery the word "cause" can be in physics, it tends to be tied to interpretations of theories moreso than to demonstrable truths, and this is sometimes a trap. In the final analysis, "causes" are always sociological constructs, albeit important ones, but physics tends to be quite uneasy about the whole concept.
DaveC426913
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Apr19-12, 05:40 PM
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Quote Quote by Ken G View Post
But in a sense, it is a "gravitational" affect in the larger sense of general relativity,
Explain this one again?

The Earth revolving around the sun causes parallax of the nearby star against the backdrop of the galaxy, meaning we can measure its distance.

How exactly is that a gravitational effect? Even 'in a sense'?
Ken G
#18
Apr19-12, 09:27 PM
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Quote Quote by DaveC426913 View Post
Explain this one again?

The Earth revolving around the sun causes parallax of the nearby star against the backdrop of the galaxy, meaning we can measure its distance.
Statements like that are frame-dependent. You have chosen the frame of the Sun, in which the Earth moves. But in the frame of the Earth, the Earth does not move. This is a perfectly inertial frame in general relativity, because the Earth is a free particle with no forces on it following an inertial path, and the spacetime around it is curved by the same history that brought us the Sun (sticking to the equations of GR rather than sociological causal judgements about what "causes" that curvature). This spacetime history will also dictate that light from another inertial frame, that of the white dwarf, will appear to "wiggle". This wiggle is a property of the fact that the light is emitted by the white dwarf and absorbed at Earth, it doesn't have any meaning in any other context that isn't purely sociological. Since the Earth is a key player in that relationship, whatever may be said to be Earth's motion is also causative of the apparent wiggling of the white dwarf. If we strip away all the sociology and just stick to the equations of the physics, then the wiggle is a property of the frames involved and the spacetime that connects them, and so is a wiggle of neither the Earth nor the white dwarf, the only thing wiggling is the angle of the light relative to a fixed standard of reference on the Earth, as described by the equations of general relativity.
How exactly is that a gravitational effect? Even 'in a sense'?
The only label we have for the things that general relativity does to completely inertial objects is "gravitational". So if two inertial objects exchange light signals that appear to wiggle, then this is a gravitational effect, and GR will describe it fine no matter what frame of reference we adopt-- including one in which the Earth is perfectly stationary. Frames of reference in GR are local, not global, so it is perfectly appropriate to consider both the Earth and the white dwarf to be stationary in their own frames, and GR will tell us how to connect signals between them based on the spacetime that connects them. There is very little left that can be called a "cause", other than the history of the spacetime, and the equations of GR. The mass of the Sun is mostly what is important in what the spacetime is doing that is responsible for the wiggle, so it could also be said that the wiggle is "caused" by the mass of the Sun coupled with the choice of the two relevant reference frames-- the white dwarf and the Earth. You need all three to get the wiggle, so will the true "cause" please stand up! Yet had the researchers said that the mass of the Sun causes the light to wiggle, it would have created even worse confusion.

(Of course, you might be tempted to point out that nothing in this problem manifestly requires general relativity, so if we adopt a more approximate but more generally understood theory, like Newton's, it will a spawn a different language for talking about the "cause" of the wiggle. This is perfectly normal and is part of what I'm saying-- we choose the language when we choose the theory, and choices of theory are essentially a part of the "sociology" of attributing causes. None of this contradicts your point that the article can lead to pseudoscientific confusions, I just find it interesting how slippery is the whole issue of causation in physics.)


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