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.Close by? Strange!
"Your planet Earth is soooo fat (how fat is it?) - it causes a wiggle in SDSS J110217, 48+411315.4's motion! BOOyah!"We found its distance by measuring a tiny wiggle in its path caused by the Earth's motion...
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.Journalists are victimized by scientists who feed them just enough information to overload their simple, disordered neural networks.
From the paper: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?
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.The initial-to-final
mass relation for WDs indicate that the progenitor of J1102
was a 1.8-2.2 M⊙ star (Catal´an 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
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.
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.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.
Explain this one again?But in a sense, it is a "gravitational" affect in the larger sense of general relativity,
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.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.
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.How exactly is that a gravitational effect? Even 'in a sense'?