Saturday, February 12, 2022

fielded a romp of questions

Yesterday, a friend asked me about black holes. A lot of questions about black holes. A pandemonium of questions about black holes! I had to noodle on them for a while...

These were triggered as they watched a talk offered from the David Dunlop Observatory, presented by Dr Saeed Rastgoo.

How is it that a black hole could potentially be older than the universe?

Why are black hole accretion disks flat and not spherical?

How does a black hole seem to have endless depth, but also seem to not take up an endless trail of space behind them? 

How does it hold everything it sucks into itself?

Do we have any white holes in our universe?  Or in our galaxy?

If not, does this point towards the existence of the multiverse?  Is the concept of a multiverse proven thus far in any way?

We have black holes in our galaxy, correct?

He talked about black holes being opposite white holes, with wormholes in between.  Um, what?

So, is this really a means of space travel, such as in Interstellar?

Aside from the fact that we could not transmit from within a black hole, or guarantee our survival inside of one.

I replied.

I can't answer all these questions.  And, arguably, it is difficult or impossible to answer all as it goes simply beyond what we really know.  And also it gets into the quantum domain, where normal physics does not apply.  And that hurts my brain.

I have not heard that black holes are older than the Universe.  That's a new one to me.  But they do appear to be old objects, as opposed to new recent phenomena.

Accretion discs are flat for the same reason solar systems and spiral galaxies are shaped the way they are.  They are spinning so there's angular motion and you get conservation of motion and conservation of energy.  At the early stages in the formation of an object, everything is going every which way.  But as it spins, a disc forms.  The rogue objects get kicked out or pulled into the disc.

A black hole does not "hold" content, it does not hold material.  As material "falls" in it converts to energy, usually extraordinary amounts of E.  E=mc^2.

I don't know about white holes.  Years ago I thought quasars were white holes but they are not.

There are lots of ideas about the multiverse and how to detect it.  I don't know a lot about it.  Ask Charles!

Science fiction has played around a lot with black holes and white holes and tunnels through space-time but I don't know much about current active theories.  The discussion in Interstellar shows a classic presentation of a 2-D surface folded or bent so they touch;  they are not far apart now.

Yes, we have black holes all around us.  There are small ones and they are probably everywhere in a galaxy.  E.g. Cygnus X-1, about 6100 light-years from us.  Look up the fun history of that one if you're not familiar...

But most (maybe all?) galaxies appear to have black holes in their centre, in the galactic core.  I now kind of think of galactic centre black holes as galaxy engines.

We can't directly see them but observations of the centre of our galaxy in other spectra reveal their presence.  There seem to be more than one, looping and orbiting around each other.  Or it's a single black hole in the Milky Way whipping and tossing nearby stars around.

Some galaxies have huge (er, that suggests size, but I mean mass) black holes that output a tremendous amount of energy.  Supermassive black holes or SMBH.  These power active galactic nuclei (AGN) and quasars.

Messier 87 has a SMBH.  It produces a jet of material (moving at the speed of light) that can be seen in basic astro-images.  It's the one we recently directly imaged a couple of years in radio and you can see the accretion disc which is so FREAKIN' cool.  I LOVE that we can see *behind* the black hole.

I also love the recent development of gravity wave detectors which pick up black hole mergers.  Gravity detectors are a new "sensor" or sense organ we have made.  We can now know of things happening that we didn't know about before.  It's like we were blind and now we can see.

I like the movie Interstellar because a lot of the science is really good.  But as soon as we went inside the black hole, at the end, all bets are off.  I like the tesseract representation and I like how he's strumming strings or lines in the tesseract that make gravity waves back on Earth in a different place and a different time.  This is all pure sci-fi.  Now it's supported by the best science we know but it's just some imaginative story-telling.

And I concluded with a warning: 

Whatever you do, don't fall into a Blake Hole.

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