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Trio of dead stars upholds a key part of Einstein’s theory of gravity
spɹɐʍoɔ snoɯʎuouɐ
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User ID: kaput
01-13-2018 03:23 PM

Posts: 4,446

Post: #1
Trio of dead stars upholds a key part of Einstein’s theory of gravity
Celestial orbital dance conforms with physicists’ expectations for ultradense objects

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TRIPLE THREAT A threesome of dead stars has allowed a new test of a tenet of Einstein’s theory of gravity. The trio includes a pulsar (illustrated, with bands of electromagnetic radiation in blue) in orbit with a nearby white dwarf. A second white dwarf orbits farther afield (red, upper right).

Quote:“We’re asking, ‘How does gravity fall?’” says astronomer Anne Archibald of the University of Amsterdam, who presented the preliminary result at the meeting. “That sounds weird, but Einstein says energy and mass are the same.” That means that the energy bound up in a gravitational field can fall just as mass can. If the strong equivalence principle were violated, an object with an intense gravitational field would fall with a different acceleration than one with a weaker field.

To test this theory, scientists measured the timing of signals from a pulsar — a spinning, ultradense collapsed star that emits beams of electromagnetic radiation that sweep past Earth at regular intervals. The pulsar in question, PSR J0337+1715, isn’t just any pulsar: It has two companions (SN: 2/22/14, p.8). The pulsar orbits with a type of burnt-out star called a white dwarf. That pair is accompanied by another white dwarf, farther away.

If the strong equivalence principle holds, the paired-up pulsar and white dwarf should both fall at the same rate in the gravitational field of the second white dwarf. But if the pulsar, with its intense gravitational field, fell faster toward the outermost white dwarf than its nearby companion, the pulsar’s orbit would be pulled toward the outermost white dwarf, tracing a path in the shape of a rotating ellipse.

Scientists can use the timing of a pulsar’s signals to deduce its orbit. As a pulsar moves away from Earth, for example, its pulses fall a little bit behind its regular beat. So if J0337+1715’s orbit were rotating, signals received on Earth would undergo regular changes in their timing as a result. Archibald and colleagues saw no such variation. That means the pulsar and the white dwarf must have had matching accelerations, to within 0.16 thousandths of a percent.


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"Bittersweet Symphony"
User ID: 1337
01-13-2018 03:28 PM

Posts: 459

Post: #2
RE: Trio of dead stars upholds a key part of Einstein’s theory of gravity
Threadtitle is a bit off...

The pulsar in the middle is not a dead star..

It is on it's way to death, might take a couple of million years still


5star for the thread content, thanks!

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