OT Primordial black holes are dark matter.

This was an article in my latest Science News,

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I found this,
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Which could be neat and clean. With the Higgs we could be sorta done with particle physics.

Put all those particle people to work doing something more practical. (No offense Jeroen)

George H.

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George Herold
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Now that LIGO seems to work, people should get to work and build enough of them to do some serious quasi-imaging, to accurately nail the direction the waves come from. The cost would be trivial by modern standards.

Isn't there a plan for a satellite version of LIGO?

Dark matter seems to glob around galaxies. If it is black holes, wouldn't there be a lot of small-scale gravitational lensing that could be detected?

Transfer the particle people to fusion? Have them make energy instead of using it!

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John Larkin         Highland Technology, Inc 
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John Larkin

Hmm. I thought baryonic matter had been excluded a long time ago on account of the abundance of primordial deuterium. (Assuming the BHs were made out of baryons.)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Phil Hobbs

Did I hear there is one in Italy that is going to come one line soon? I guess that's Virgo,

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Quoting from the text,

"Here we consider whether the two ? 30 M black holes detected by LIGO [7] could plausibly be PBHs. There is a window for PBHs to be DM if the BH mass is in the range 20 M < M < 100 M [8, 9]. Lower masses are excluded by microlensing surveys [10?12]. Higher masses would disrupt wide binaries [9, 13, 14]."

I guess there is some "Goldilocks" window where PBH could be DM. In a few more years with more data from Ligo we'll have a better idea of the BH mass distribution in the galaxy. (I've seen data from the other ligo events, much smaller masses, signal to noise was not nearly as good as the first detection.)

Sure, or better electronic stuff; batteries, detectors, Fet opamps... (an endless list.)

George H.

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George Herold

Geesh, I have no idea Phil. Primordial black holes, so made before(?) all the matter decoupled?

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George H.

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George Herold

IIRC the Hawking radiation signature of primordial black holes should be pretty distinct. It's not there, which either rules out the existence of Hawking radiation, or of primordial black holes.

Since both are predicted by current models, there's still work to be done.

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Tim Wescott 
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Tim Wescott

A 30 solar mass BH won't have a lot of Hawking radiation. It's the little mountain- or continent-mass ones that evaporate.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Phil Hobbs

True, but when folks start from a Big Bang and predict the mass distribution of primordial black holes, they end up predicting lots of objects of that mass. Then Hawking's work predicts that they'll be madly radiating away. Then the astronomers not only fail to find such radiation, they make a pretty good case for it not being there.

So, either the Big Bang theory is wrong (for which there is a building mass of evidence), or Hawking is wrong.

I have yet to read the article -- as of several years ago I thought the cosmological community had decided that dark matter couldn't be explained by lumps of stuff roaming around. It'll be interesting to see how well accepted the idea is.

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Tim Wescott 
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Tim Wescott

Yeah I have no idea, they would be little PBH's to decay in the lifetime of the universe. The PBH* as DM is probably wrong, but it's worth thinking about.

George H.

Reply to
George Herold

Ah. Read the article, see where they're coming from. Inneresting, but it's a whole lot of conclusion from a little bit of data.

Time will tell.

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Tim Wescott 
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Tim Wescott

None taken.

Cheers, Jeroen Belleman

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Jeroen Belleman

Yeah right one data point. The first GW event was bigger than expected for a stellar event. As JL said some more detectors, sprinkled around the globe, so we could get direction, would help.

It would be fun to work on ligo. As I understand it, it's mostly classical physics. A Michelson-Morely interferometer, supped up for the 21st century.

I must admit, black holes seems the obvious answer to dark matter and I want to know why it's wrong.

George H.

Reply to
George Herold

I had not realized when I made my original comment that primordial black holes were a candidate for dark matter at all. Presumably the fact that there's only a narrow mass range for them that hasn't been ruled out is a good part of the reason that they weren't stressed in what I've read.

More detectors would be a good thing. I gather than some $30x10^9 has been spent on the project, which is (apparently!!!) a fraction of the price of space-based telescopes. I don't know if there's a price tag for individual detectors.

Need more data, dammit!

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Tim Wescott 
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Tim Wescott

Do you think there will ever be bigger accelerators than CERN?

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John Larkin         Highland Technology, Inc 

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John Larkin

Detectors on the Earth are so much cheaper (and easier to maintain) than detectors in space.

Ok here's a crazy idea. Say there's a bunch of big BH's in the halo. Can we detect them by gravitational lensing in cheap telescopes, how fast is the typical BH moving?

George H.

Reply to
George Herold

The good data (in particle physics) is coming from astronomy. (an observational science.)

George H.

Reply to
George Herold

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It's been tried. There wasn't enough gravitational lensing going on to fit the particular dark matter model being tested, but the 30 to 100 solar mass window may reflect a hole in that data.

The search was for non-radiating baryonic matter, and they would have expec ted masses between 30 and 100 solar masses to be quite brightly radiating s tars.

Even if they'd been wrapped in a Dyson sphere, anything of that mass that w asn't a black hole would still have radiated a lot in the infra-red.

As fast as a star in the same area? Binary black holes have more complicate d behaviour. We know that when a binary star gets close to a black hole, on e star can get captured and the other star can get accelerated above the ga lactic escape velocity, because we can see a bunch of stars moving fast eno ugh to eventually escape the Milky Way. Binary black holes could presumably behave the same way.

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Bill Sloman, Sydney
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bill.sloman

Physicists are never short of ideas for still bigger projects. There are people at CERN studying the next big things, but all are long-term future ideas, say 20 to 25 years out. For the moment, we'll run the LHC until it has given everything it can.

One project is the Compact Linear Collider (CLIC), a 50km

interesting for its scheme to produce RF power, for the high- gradient accelerating cavities and for its extreme alignment precision requirements.

Another is a superconducting synchrotron that would be built in a 100km circumference underground tunnel making a wide loop around the city of Geneva.

Whether either of these projects will ever be realized is uncertain.

Jeroen Belleman

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Jeroen Belleman

tto:

there was the LISA project

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but I think they have drop ped it.

Bye Jack

Reply to
jack4747

The current Big Bang theory has plenty of workarounds and fudge-factors that have weak evidence and little logic (inflation, dark matter, dark energy, and lots of fine-tuned constants). To me, it all sounds like there is some underlying assumption in our theories that should not be assumed. Perhaps some of the "fundamental constants" are not actually constant. For example, if the gravitational constant G had varied over time, that could explain the position and speed of galaxies without having to "invent" dark energy. Of course, you then need to have an explanation and mechanism for G to vary - and clearly it is not /so/ simple or some real physicist would have figured it out already.

That was my impression too. And I also thought that any primordial black holes would have been small, and therefore have evaporated.

But maybe the small primordial black holes collided enough to grow big enough. Or maybe the earliest galaxies produced more black holes than we thought - and more of them are still wandering around in galaxies rather than having collected at galactic centres.

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David Brown

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