How do they measure stars thousands of light-years away moving 7 mm a day towards each other in a double pulsar system?

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So I saw a short on YouTube talking about how they proved a prediction Einstein made about double pulsars falling towards each other at the rate of 7 mm a day. My question; how the hell can they measure two stars that are roughly the size of LA, but the mass of our sun, moving 7 mm closer each day while in orbit of each other lightyears away? At that distance it’s gotta be a couple pixels on whatever they’re using to view them right?

In: Planetary Science

2 Answers

Anonymous 0 Comments

“A couple of pixels” is a reasonably accurate estimation. We cannot measure the distance between them this way. We can detect things like alignment of the two, or when a pulsar’s pole is pointing our way, however.

There is a workaround. Orbits follow a set of rules. And if the masses of the two don’t change significantly but the orbit becomes smaller, then it also becomes faster. And these events would become more frequent at a very specific and very predictable rate.

We might not have telescopes that can measure the distances between two stars to within a centimeter. We do, however, have very very accurate clocks.

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