General relativity passes a range of precise tests set by pair of extreme stars | Hacker News Reader

General relativity passes a range of precise tests set by pair of extreme stars

mpifr-bonn.mpg.de

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“ This cosmic laboratory known as the “Double Pulsar” was discovered by members of the team in 2003. It consists of two radio pulsars which orbit each other in just 147 min with velocities of about 1 million km/h. One pulsar is spinning very fast, about 44 times a second. The companion is young and has a rotation period of 2.8 seconds. It is their motion around each other which can be used as a near perfect gravity laboratory.

Prof Dick Manchester from Australia's national science agency, CSIRO, illustrates: “Such fast orbital motion of compact objects like these - they are about 30% more massive than the Sun but only about 24 km across - allows us to test many different predictions of general relativity - seven in total! Apart from gravitational waves, our precision allows us to probe the effects of light propagation, such as the so-called “Shapiro delay” and light-bending. We also measure the effect of “time dilation” that makes clocks run slower in gravitational fields. We even need to take Einstein's famous equation E = mc2 into account when considering the effect of the electromagnetic radiation emitted by the fast-spinning pulsar on the orbital motion. This radiation corresponds to a mass loss of 8 million tonnes per second! While this seems a lot, it is only a tiny fraction - 3 parts in a thousand billion billion(!) - of the mass of the pulsar per second.”

It’s so beautiful that these things are just existing out there with such intensity that we would die instantly if we tried to see it.

My jaw (and my phone) dropped when I read the numbers. I feel like space is ruthlessly huge and these pulsars are brutally massive..

https://en.m.wikipedia.org/wiki/TON_618

This black hole is 66 billion solar masses. Its mass is greater than that of our entire galaxy. The quasar shines with the power of 140 trillion suns. The event horizon radius is times 40 times the distance from Neptune to the Sun. Matter is getting sucked into it at 7000km/s

As with most amazing space-related things, Anton Petrov has a wonderful video talking about TON 618, using Universe Sandbox (which is quite fun to play in!) to demonstrate its size in comparison to our solar system. It helps, to an extent, to visualize just how large it is.

https://www.youtube.com/watch?v=Vn9Xuema8q4

Small nit: I think the Wikipedia entry is saying TON 618's mass is greater than all of the stars in our galaxy (6*10^10 solar masses, according to the article), not greater than the entire mass of the galaxy (~10^12 solar masses, according to the Milky Way article).

TON 618 is a quasar, which according to Wikipedia "is an extremely luminous active galactic nucleus (AGN), powered by a supermassive black hole, with mass ranging from millions to tens of billions of solar masses"

"More than a million quasars have been found".

Wild.

It's interesting how we talk about these far off things using the present tense, because technically we should replace every use of "is" in your post with "was".

True. In the case of that monster, unless it ran out of galaxies to eat, it's still there nomming. Perhaps the only thing that has changed is the size of it.

This is why we need to develop very precise warp drive exit techniques. Don’t want to exit warp inside the horizon.

Traveling through hyperspace ain't like dusting crops, kid.

Additionally, I love the challenge to language. These stars _are_ massive... but also tiny. Compare their 24 km radius to the 600,000 km radius of the sun. One of these objects would sit comfortably inside many Earth cities.

... at least for a milisecond before destroying it.

Now imagine that 24km object, something three times bigger than the biggest mountain on Earth, spinning 44 times a second!!! Of course, we can't even begin to imagine that this huge mountain also has the mass of the whole Earth, let alone the mass of the whole solar system (it's actually even more than that).

Just completely mind blowing.

If you see "massive" in reference to an astronomical object, it usually means "having a lot of mass" rather than "being very big".

Not always of course, and the latter usage is more likely in less specialized news sources.

And the energy lost between Sum and Earth due to gravity waves is sufficient to power a small toaster oven.

To put this in perspective, our sun loses around 4 million tons per second, so it is about twice the radiation of the sun

This does worry me, though https://en.wikipedia.org/wiki/Flyby_anomaly

> The analysis of the Juno flyby looked at analysis errors that could potentially mimic the flyby anomaly. They found that a high-precision gravity field of at least 50×50 coefficients was needed for accurate flyby predictions. Use of a lower-precision gravity field (such as a model with 10×10 coefficients, sufficient for launch analysis), would yield a 4.5 mm/s velocity error.

I buy this explanation as the most likely vs any other more esoteric explanation.

This was an absolutely fascinating read. Thanks for sharing!

Neutron stars are just insane.

> It is the only system of two radio pulsars known to date. The source, in a distance of 2400 light years

What a find!

That is what astonishes me. I thought these things would have to be 24 million light years away, not just 24 hundred. That is practically our backyard.

Radiating away 8 million tons per second, and barely noticing the loss.

I marvel that these things aren't magnetars. We will be lucky if no magnetars are found within 500 ly, because a minor disturbance on one that close could end life on Earth. Life in a galaxy is a risky affair. Anybody capable would get far away from the galactic disc, as soon as possible, if they value life. It is no surprise they don't visit us. It is dangerous here.

It's not as if anyone was expecting General Relativity to fail the test. Gravitational time dilation is a thing observed since the 1970s, atomic clocks have compensation for altitude and gravitational potential applied to them and that's part of the TAI and UTC standards we use every day, knowingly or not.

On the other hand, Einstein lost his vendetta against Quantum physics, badly, since Alain Aspect's 1980 experiment showing Bell's inequalities are violated.

Einstein did not really have a vendetta against Quantum physics. He won a Nobel for having established the basic theory of the photoelectric effect. I know what you mean, but it's not like he thought the idea was ridiculous, he came up with it in his youth.

Fantastic! Was the orbit of Mercury early in the 20th centruy the first confirmation?

It was known since the 1850s that the perihelion precession of Mercury is a few percent larger than predicted by Newtonian mechanics. This even led to speculations that there might be another undiscovered planet ("Vulcan") in a close orbit around the sun. In 1916 Einstein calculated that this effect could be fully explained by General Relativity. Another famous prediction is that of the deflection of light that passes close to a star. This was confirmed by Eddington during the 1919 solar eclipse.

Light deflection happens in newtonian physics as well, assuming you use Newton's definition of light as a particle/corpuscule: https://physics.stackexchange.com/questions/29837/does-newto...

It's just 2x the GR value. That's one reason why it took so long to verify as you needed to have pretty clean data to rule out the classical explanation.

I don't think that anyone took the corpuscular theory of light seriously after its wave nature had been discovered in the early 19th century. In classical electrodynamics, light is completely unaffected by gravity.

It's not even nine nines? Only 99.9%

I think you've got a typo, it was 99.99%. "Einstein’s theory, which was conceived when neither these types of extreme stars nor the techniques used to study them could be imagined, agrees with the observation at a level of at least 99.99%." Either way, incredible stuff. I'm impressed the experimental data is that accurate.

As Lenny Suskind put it, "they didn't call him Einstein for nothing!".

This is a good one haha, thanks for sharing — would love a primary source if you know it off the top of your head!

It was apparently a line from one of his general relativity lectures.

Gosh, this must be really special research: "extraordinary", "unprecedented", "superb".

I was really hungry, and the menu looked pretty tasty; but the service was slow, so I left.

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