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Ever wondered why the universe only has black holes in S or XXXL? No? Boffins have an answer

Meh

Rare?

Did I read that wrong or was the implication not that the middle-sized ones were merely considerably harder to detect, rather than provably rare?

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Re: Rare?

It's argued they're rare, but easy to detect, close up; and become more common, but harder to detect, as you move further away.

That said, it's a tendentious proposal.

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It's "Dwarfs", not "Dwarves", unless you're Tolkien.

</pedantry>

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Paris Hilton

It's "Dwarfs", not "Dwarves", unless you're Tolkien.

Or Disney?

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Facepalm

Re: It's "Dwarfs", not "Dwarves", unless you're Tolkien.

Or the OED*.

*Dwarf: noun (plural dwarfs or dwarves)

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Anonymous Coward

Re: It's "Dwarfs", not "Dwarves", unless you're Tolkien.

I suspect that if you find a copy of the OED from pre-Tolkien times, Dwarfs might be the only variant. Tolkien explains in detail in Lord of the Rings about how middle earth explicitly uses Dwarves instead of the English Dwarfs, and given that he is a philologist by profession, I suspect we was completely correct. But since the OED decides which words go into the dictionary based on a caucus of text which, post-Tolkien, will have only grown in use of Dwarves, that would account for the change.

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Re: It's "Dwarfs", not "Dwarves", unless you're Tolkien.

Maybe he should have used Dorfs or Dorks.

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Re: It's "Dwarfs", not "Dwarves", unless you're Tolkien.

"t. Tolkien explains in detail in Lord of the Rings about how middle earth explicitly uses Dwarves instead of the English Dwarfs"

And later admitted he was covering up a simple mistake with BS.

Even philologist can get it wrong sometimes.

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Coat

Just a Germanic oddity with the "v" and the "f" being equal and a bit "undecided".

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Boffin

Pfft, fake science...

It's obvious that whatever it is that makes up all that dark matter views black holes as snacks, and the little ones are too small, and the big ones...Well, just because you are a universe-spanning mega-fauna doesn't mean you have to make a pig of yourself.

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Baby Astrolab

http://www.lyrics.com/lyric/1223049

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Black Holes are just like grocery stores...

You either have your Spa corner shop or your Sainsbury's. It's very rare to get a medium sized grocery store.

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Re: Black Holes are just like grocery stores...

Can corner shops grow by accreting customers?

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Can corner shops grow by accreting customers?

The analogy was referencing the size through comparing event horizon (as opposed to solar masses) to turnover (rather than customer numbers), and therefore, in essence the grocery store grows by accreting stock. It does this by sucking in money - in the cosmology of the shopping mall greed = gravity.

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Re: Black Holes are just like grocery stores...

Well, it almost worked for Sweeney Todd.

Mmmm Long Pork Pies...

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Re: Black Holes are just like grocery stores...

Does copious amounts of banana flavour vaping smoke act the same as an stellar accretion disc?

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Re: Black Holes are just like grocery stores...

A spa is a mineral spring.

A Spar is a small supermarket.

</pedantry>

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Joke

Re: Black Holes are just like grocery stores...

> Can corner shops grow by accreting customers?

Yes. Accreted customers are often seen in Walmart, ergo corner shops grow into Walmarts. QED!!

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A spa is a mineral spring...

Oops.

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Re: Black Holes are just like grocery stores...

Where does Morrisinghs fit in?

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where does Morrisinghs fit in?

About the size of a brown dwarf obviously :-)

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How come...

How come the super-massive black holes haven't sucked up all the dark matter?

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Re: How come...

Same reason they haven't sucked up all the surrounding galactic stars and dust

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Boffin

Re: How come...

So which wins, the expansion of the Universe or all matter being sucked into a Super Massive Black Hole?

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Boffin

Re: How come...

Expansion wins, and it is not even a contest.

Short version is that the universe will expand to the point where we will not even be able to detect anything beyond our own cluster of galaxies. And with time even the galaxies themselves will scatter. And then there will black holes roaming the place and slowly evaporating.

First, let us just state the fact that the gravity from black holes is a function of their mass as everything else. The fact that they are black holes does not change how gravity behaves. The only special thing about them are that they are so dense that you can get extremely close to their centre. And since gravity is a function radius squared it will eventually be so great that light can't escape. However, if you collapse the moon to a black hole and manage to keep it stable, the effect on Earth will mostly not be noticeable except that there will be no moonlight. https://what-if.xkcd.com/129/

With that in mind we can look at the size of the universe and current theories to see that it is ever expanding. If a black hole gobbles up a nearby star this will have no effect on the pull of far away objects. Their combined mass and centre of gravity is more or less the same before and after the event. While it is true that galaxies collide from time to time that is on "local" scale and the general rule is still that the further away you go the faster everything moves away from us. Making everything in the "local" area one object will not change that. More about the structure of the universe as it is now: https://www.universetoday.com/37360/structure-of-the-universe/

Thus the best thing a black hole can hope for is to gobble up everything nearby, meaning it's own galaxy and maybe the one next over. However even that will not happen. Grab some empty space without anything affecting it, even from the outside. Throw three objects into and unless you throw them to hard they will start to orbit each other. But the orbits will be chaotic. And they might collide, but that is actually quite unlikely. Since volume and thus mass is a function of radius cubed and gravity is a function radius squared, gravity tends to become a rather strong force when you grow the size to astronomical bodies. Just look out how far the pull of the sun goes compared to the radius of the sun itself. So since they won't hit each other they will create an infinite number of different orbits, until two of the objects manage to work together in such a way that they will eject the third (usually the smaller) out of the system all together. Now then, do this on a galactic scale with a huge number of objects and you will eventually scatter all, but two objects (usually the bigger ones). So what makes black holes eat matter at all then? The answer is friction, either tidal friction within the stars or friction in gas and dust particles which allows them to slow down their orbital speed enough to fall into the hole. https://en.wikipedia.org/wiki/Future_of_an_expanding_universe#Stellar_remnants_escape_galaxies_or_fall_into_black_holes

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An alternative theory

All the black holes in this universe were bought in a sale. Just like clothing or shoes in sales, there's lot of the very small and the very large, but nothing in the medium sizes because they were sold before the sale.

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Re: An alternative theory

That's what the department stores say, but it explains nothing.

The first season the store is in business, maybe. After that, the store should have a fair idea of how many of each size they can sell at a regular price.

So if they end up with a bunch of odd sizes that they have to get rid of with a deep discount, then somebody isn't doing his homework.

To put it another way: Why shop at a store run by the same people who used to cheat off you in class, and make fun of you on the playground?

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Wheeler wasn't first to label them "black holes"

He just popularised the name.

http://www.worldwidewords.org/topicalwords/tw-bla1.htm

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Maybe they are like funnels between realities

You have the thick end or the thin end, galactic snakes and ladders.

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Re: Maybe they are like funnels between realities

More like a mincer between realities.

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Coat

So just like shopping then

Same old story. They never have the size you are looking for .

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Bah!

Glaciers melting in the dead of night!

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Angel

Assumptions

Perhaps 'S' is an assumption?

Perhaps there aren't any, and any smaller ones are not detectable at this moment in time.

If (and when) a smaller one is detected, then all the 'S',s will become 'M''s.

Of course if a FBO is detected, then it will be an XXXL, and all the existing XXXL's will be 'S',s unless a 'M' has been found.

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Anonymous Coward

Sorry, but I am still not buying it...

This article said NOTHING, except that medium sized black holes are "tricky to find". Tricky to find? Seriously? I can understand their reasoning behind the supermassive black holes. But what? A small black hole of 30 to 40 suns stops at 30 to 40? That's only 300,000 years of solar mass gathering at (their) the given rate of 1 every 10,000 years. The age of the milkyway is 13.21 billion year old... what were those 30-solar-mass black holes doing for the first 13 billion years? Did they all just form 300,000 years ago? And if they formed MORE than 300,000 ago, then what happened to the "one solar mass every 10,000 years" metric that they DEPEND on to make this article look plausible?

Their reasoning is full of obvious black holes.

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Re: Sorry, but I am still not buying it...

The 'growing at the rate of one solar mass every 10,000 years' is for supermassive black holes at the center of galaxies only. It does not apply to the small black holes that are remnants of stars. A few might get lucky and have another star move close enough it can be captured and eventually "eaten", but that's going to be quite rare.

Generally a stellar mass black hole remains roughly the same size forever - there is no mechanism for it to get bigger. If the Sun was transformed into a black hole, it wouldn't swallow the planets, let alone other stars. After all, it has been there for about 5 billion years, and has swallowed no other stars, nor Mercury, Venus, Earth, etc. Since the destructive act whereby a star (more massive than our Sun) becomes a black hole costs it a lot of mass, its ability to swallow other stars is actually reduced after its life as a black hole begins, making it even less likely to do so than when it is a star.

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Anonymous Coward

Re: Sorry, but I am still not buying it...

Well, you see, the thing is that the colour of space, your basic space colour, is its black. So how are you supposed to see a black hole?

Where would we be without Red Dwarf.....

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