Galaxy's end

[eosophobiac]

After reading this article:<br />http://skyandtelescope.com/news/article_1654_1.asp<br />I was wondering what happens when the black hole at the center of a galaxy has 'consumed' all the matter it had? It is understood that it takes many, many years for this to even come close to happening, but the article didn't seem to touch on what happens when there is nothing left to be pulled in by the black hole. (I hope I worded it correctly.)<br />Anyway, any thoughts? Links are always appreciated, as well.<br /><br /> <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[rodrunner79]

I do not have a direct answer to the OP (original poster). However, I do have a question that pertains to blackholes. What happens when the BH on the core of galaxies evaporate? What effects will it have on the stars, planets, and other objects? Will they still stay in orbit and circle where the BH was once at?

 

[Saiph]

well...when nothing is going it, no light is produced near it by the accretion disk. So we can't see any direct signs it's there. Things will still orbit it, so we could detect it that way (seeing stars spin in circles with no visible reason...).<br /><br />And since <i>nothing</i> is going in, the slow rate of evaporation due to Hawking radiation will slowly shrink the size of the BH (very, very, very slowly).<br /><br />If the BH manages to fully evaporate (in 10^50 years IIRC...so in a long, long, long time)...anything still orbiting it will have slowly receeded away an stop orbiting it.<br /><br />The smaller the BH gets, the looser the orbits around it, so the objects receed just a bit. This is because the mass that was formerly in the BH, is radiated away, and heads elsewhere. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[eosophobiac]

Thanks much for the response, Saiph.<br /><br /> <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[newtonian]

Saiph - I do not understand why matter released from a black hole by Hawking radiation would not summarily be reabsorbed by black hole gravity.<br /><br />Or is it energy, rather than matter, that is radiated, and hence achieves escape velocity beyond the event horizon?

 

[newtonian]

eosophobiac - I do not know - but why the big bang happenned in the first place might help - since the singularity had some similarities to a super supermassive black hole with all energy within it (or provided from outside the system thermodynamically - as in God creating the universe).<br /><br />Why do you feel the galaxy will end? <br /><br />Do we have any observational evidence of any galaxy ending?<br /><br />I understand that not all galactic orbits are decaying - in fact not all are gravitationally bound though certainly most are.<br /><br />Orbits do indeed usually decay - but there are significant exceptions - notably our moon! <br /><br />And galactic mergers, such as the upcoming Andromeda-Milky Way merger, certainly will upset the established galactic arm orbits.<br /><br />There will clearly be gravitational tug of wars between supermassive black holes.<br /><br />Compare what has happenned in the more massive gravitational tug of war between great attractors wherein thousands of galaxies including Milky Way are breaking off from one attractor and streaming towards the Great Attractor.<br /><br />Do we have any computer simulations detailed enough to determine which supermassive black hole our sun will ultimately be gravitationally bound in some 10-100 billion years: namely the Milky Way BH or the Andromeda BH?

 

[harmonicaman]

End of the universe:<br /><br />Timeline<br />Lecture<br />Older Article<br />Another View

 

[nexium]

The Saiph answer is interesting for several reasons. 1 Capture of nothing, not even a photon or sub atomic particle is hard to imagine before it evaprorates to a few grams, as a typical BH will recapture some of it's own Hawking radiation sooner or later. 2 If things are receeding from typical black holes with no (or negligible) acreation disk, then Earth and the other planets should be receeding from our Sun how many millimeters per century? Our sun has a net mass loss most centuries? Neil

 

[newtonian]

Neil - Actually there are different calculations for earth's future orbit - and the decrease in solar mass is a factor.<br /><br />So is solar wind.<br /><br />I do not know the net effect of tidal interactions between earth and sun on earth's future orbit.<br /><br />Does anyone know?<br /><br />Don't forget effects of magnetic fields!

 

[vogon13]

If I understand Hawking's explanation of his eponymous radiation correctly, the wavelength of the escaping radiation will correlate to the physical dimensions of the EH. Recapture of successfully emitted radiation would be unlikely unless the photons were reflected back.<br /><br />The emitted radiation would be subject to gravitational red-shifting though, and perhaps this effect could be rather large.<br /><br />The spectrum of the emitted radiation would still be Gaussian.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[newtonian]

harmonicaman - a sense of humor! (another view)<br /><br />From the first link, which I disagree with:<br /><br />The Stellar Era Ends<br />100 Trillion Years in the Future<br />Astronomers assume that the universe will gradually wither away, provided it keeps on expanding and does not recollapse under the pull of its own gravity. During the Stelliferous Era, from 10,000 years to 100 trillion years after the Big Bang, most of the energy generated by the universe is in the form of stars burning hydrogen and other elements in their cores. <br /><br />The Degenerate Era<br />100 Trillion to 10^37 Years in the Future<br />This era extends to Ten Trillion Trillion Trillion years after the Big Bang. Most of the mass that we can currently see in the universe is locked up in degenerate stars, those that have blown up and collapsed into black holes and neutron stars, or have withered into white dwarfs. Energy in this era is generated through proton decay and particle annihilation.<br /><br />The Black Hole Era<br />10^38 to 10^100 Years in the Future<br />This era extends to Ten Thousand Trillion Trillion Trillion Trillion Trillion Trillion Trillion Trillion years after the Big Bang. After the epoch of proton decay, the only stellar-like objects remaining are black holes of widely disparate masses, which are actively evaporating during this era. <br /><br />The Dark Era<br />Times Later than 10^100 Years in the Future<br />At this late time, protons have decayed and black holes have evaporated. Only the waste products from these processes remain: mostly photons of colossal wavelength, neutrinos, electrons, and positrons. For all intents and purposes, the universe as we know it has dissipated.<br /><br />Part of the problem is that this view assumes (note the statement "astronomers assume") not only that our universe will expand eternally (which I tentatively agree with, with the exception of the thousands of galaxies including Milky Way heading for the Great Attractor) but also that our unive

 

[rodrunner79]

Thanks for the links harmonicaman, very interesting reading.