
‘Radical change’ needed after latest neutron star collision - theafh
https://www.quantamagazine.org/radical-change-needed-after-latest-neutron-star-collision-20200220/
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rwallace
> Based on the recent observation, LIGO scientists estimate that these heavy
> pairings should be almost as common as the lighter binary star systems that
> astronomers have been studying for decades. Big neutron star pairs should be
> all over the universe, including our own Milky Way. Why, then, have they
> never been spotted before?

I don't understand this part. Observations: lots of light neutron star pairs,
one heavy pair. This implies heavy pairs are as common as light pairs? How? I
would've thought it implied heavy pairs exist but are much less common. What
am I missing?

~~~
sfink
The observation of lots of light pairs was from directionally focused visible
light telescopes, which is a very heavily biased estimator.

LIGO has flipped a weighted coin twice. It came up heads once, tails once.
That suggests that the weighting is probably not 999999 to 1 (or whatever 5
sigma works out to) in favor of heads, as the current models (based on visible
light observations) predict.

~~~
amerine
Your second paragraph is an excellent summary of why this data is super
impactful.

Curious about the “but the sample size” crowd.

~~~
perl4ever
I was thinking the other day along these lines - statistically, I am most
likely to be born when the world's population is at its peak. But apparently
it is still growing and has been since I was born. Is this surprising? Is it
more surprising if it continues?

~~~
simonh
Prior probability will tell you a lot about populations, but very little or
nothing about individuals.

For example the prior probability of someone being born with your specific
genetics is so close to zero it’s not worth mentioning. That’s true of any
specific combination, yet humans exist and so it’s guaranteed that some
combinations get to ‘win the lottery’. It’s just not knowable beforehand which
ones. In the context of a specific outcome though, and only that context,
prior probability just doesn’t matter.

I think the problem is our brains can’t help ‘polluting’ the context of an
outcome with unrelated contingent information. This makes it very hard for us
to reason about these questions.

~~~
perl4ever
"For example the prior probability of someone being born with your specific
genetics is so close to zero it’s not worth mentioning."

I don't understand what this has to do with distinguishing between individuals
and populations. You could just as well say that the probability of a whole
population being exactly as it is, is even lower.

You reference "polluting the context of an outcome with unrelated contingent
information", but isn't that what you just did? If you think that confuses the
issue, then what's the point?

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ISL
This presumes that the merger was a neutron-star binary. If the progenitors
were black holes, there's no need to rethink nuclear physics.

One would then have to contend with estimating the rate of stellar-mass black-
hole mergers, but at least there's no need to break our understanding of QCD
at the same time...

Time will tell. As the gravitational-wave detectors trigger on more neutron-
star mergers with optical counterparts, the answers will become clear. If
there are lots of events without optical counterparts, they're more apt to be
black holes.

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mynegation
Not an astrophysicist so it might be a stupid question. If the combined mass
of the pair is calculated to be well outside the range of what we find in our
galaxy, could it be that it is not the mass but some other inputs to the
calculation? From what I understand there is still a challenge to determine
distances to the very far objects (that is one of the reasons for recent news
about “Hubble not so constant”)

~~~
magicalhippo
In this[1] article, they show how one can estimate the distance using only
measurements of the gravitational wave signal. It uses the fact that we can
estimate the masses[2] based on the change in frequency of the chirp signal.

[1]: [https://arxiv.org/abs/1602.04666](https://arxiv.org/abs/1602.04666)
(pages 15-16)

[2]:
[https://en.wikipedia.org/wiki/Chirp_mass](https://en.wikipedia.org/wiki/Chirp_mass)

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ncmncm
We are barely beginning to understand things about the universe, based almost
entirely on wholly local observations. Nothing seen in the wider world should
be considered surprising or out of bounds. Expecting to be able to simulate
the development of the whole universe accurately with our primitive sticks-
and-rocks equipment is nothing short of foolish. Do we see things different
from what we predicted? Fine, we see them. It's a big universe, and we have
another billion years to figure it out, provided we manage not to blow
ourselves up first. The next generation will not lack for mysteries. Savor
them.

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AtlasBarfed
Can't the larger number of massive pairs be explained by a third star that was
torn apart and fed the pair, rather than limiting to supermassive originating
stars?

The other implication of the article is that they want to consider a supernova
that spawns two neutron stars, or just bigger neutron stars?

