Astrophysics and Cosmology - Discuss the Universe here

[Agent : Orange]

This is a good illustration of why one team's result does not constitute science in the absence of repeatability.  I think I personally put too much faith in that result as it seemed to verify a number of fundamental but as yet undemonstrated principles.

BICEP2 is still not completely off the table (unlike the tone taken in the article above) but it's in a more critical condition than it was before these Planck results were released. I was really hoping it would be verified, when/if primordial gravitational waves are finally detected they will give up a treasure trove of fundamental results. We now have to wait for the upcoming paper in November which will hopefully give a more definitive statement than this. But the situation looks grim for gravitational wave fans.

[zeebo]

...But the situation looks grim for gravitational wave fans.

Great, more bad news.  First Honey Boo-Boo's Mom & Sugar Bear split up, and now it seems my grav wave dream is on the rocks. 

Well now that I'm depressed, I'll just gaze at this cool pic of the nearly edge-on Sombrero Galaxy to perk up my spirits.  It's only 28 million light-years away, so if things don't pick up for me soon around here, I'm just gonna head on over.

[GeorgieForPresident2216]

Great, more bad news.  First Honey Boo-Boo's Mom & Sugar Bear split up, and now it seems my grav wave dream is on the rocks. 

Well now that I'm depressed, I'll just gaze at this cool pic of the nearly edge-on Sombrero Galaxy to perk up my spirits.  It's only 28 million light-years away, so if things don't pick up for me soon around here, I'm just gonna head on over.

That's crazy talk.  You'd need some sort of squirrel cannon to get there.   Beautiful pic though

[area51drone]

Great, more bad news.  First Honey Boo-Boo's Mom & Sugar Bear split up, and now it seems my grav wave dream is on the rocks. 

Well now that I'm depressed, I'll just gaze at this cool pic of the nearly edge-on Sombrero Galaxy to perk up my spirits.  It's only 28 million light-years away, so if things don't pick up for me soon around here, I'm just gonna head on over.

I have been so impressed with the 9"-14"  scopes people have on NSN, they can get really good video of these objects, so much better than I expected to see from a home setup.

[wr250]

Researcher shows that black holes do not exist
Black holes have long captured the public imagination and been the subject of popular culture, from Star Trek to Hollywood. They are the ultimate unknown â€" the blackest and most dense objects in the universe that do not even let light escape. And as if they weren't bizarre enough to begin with, now add this to the mix: they don't exist.
By merging two seemingly conflicting theories, Laura Mersini-Houghton, a physics professor at UNC-Chapel Hill in the College of Arts and Sciences, has proven, mathematically, that black holes can never come into being in the first place. The work not only forces scientists to reimagine the fabric of space-time, but also rethink the origins of the universe.
http://phys.org/news/2014-09-black-holes.html

original paper : http://arxiv.org/abs/1409.1837

[Gd5150]

Wow!!! If that is the case, it would turn the astrophysics world on its head.

[DigitalPigSnuggler]

Wow!!! If that is the case, it would turn the astrophysics world on its head.

https://www.youtube.com/watch?v=ssta0_4GkRA

There no proof, at all, outlined in the article, and in addition there are some fundamental errors in the description of the process.  The most glaring being her claim (or so says the article) that "as a star collapses under its own gravity, it produces Hawking radiation. "  Hawking radiation is produced when a black hole is already present.  The amount of mass lost by Hawking radiation occurs at a minuscule rate.  It would not occur rapidly enough to prevent the collapse of all stars into black holes in any case.

It could be that the article is fucked up, but I do note that nobody other than the university and the media are talking about this, so that does not bode well for this "discovery" either.  It also does not mention any new math or new information that led to this kind of analysis, which makes one wonder why somebody like Hawking didn't spot it before now, rather than a prof six years into tenure.

She's a hottie, though, I will give her that.  I'd take her 'round the universe, and all the other places too.

[DigitalPigSnuggler]

Found another couple of things related to this "discovery" about black holes not existing.

First, the author didn't submit her paper for peer review.  That's a big, fat, big-titted red flag when you consider her claim: to have reconciled quantum mechanics and relativity, which is a holy grail of physics.

Second, this:

"However, not everyone is on board with Mersini-Houghton’s conclusions. William Unruh, a theoretical physicist from the University of British Columbia, pointed out some fatal flaws in the paper's argument.

“The [paper] is nonsense,” Unruh said in an email to IFLS. “Attempts like this to show that black holes never form have a very long history, and this is only the latest. They all misunderstand Hawking radiation, and assume that matter behaves in ways that are completely implausible.”

According to Unruh, black holes don’t emit enough Hawking radiation to shrink the mass of the black hole down to where Mersini-Houghton claims in a timely manner. Instead, “it would take 10^53 (1 followed by 53 zeros) times the age of the universe to evaporate,” he explains.

“The standard behaviour by such people [who don’t understand Hawking radiation] is to project that outgoing energy back closer and closer to the horizon of the black hole, where its energy density gets larger and larger,” he continued. “Unfortunately explicit calculations of the energy density near the horizon show it is really, really small instead of being large-- Those calculations were already done in the 1970s. To call bad speculation "has been proven mathematically" is, shall we say, and overstatement.”"

[Gd5150]

Oh well it was fun while it lasted. Guess we can all go back to looking forward to ending up in a singularity one day.

[Agent : Orange]

That paper has some big problems. DPS nailed it. Don't take the results too seriously!

Aside from the obvious problems, we've already observed objects which are too small and massive to be explained by anything other than a black hole. Which doesn't mean anything about singularities, admittedly. But what we see through telescopes gives us a pretty strong hint that something like what we call black holes are out there.

[wr250]

That paper has some big problems. DPS nailed it. Don't take the results too seriously!

Aside from the obvious problems, we've already observed objects which are too small and massive to be explained by anything other than a black hole. Which doesn't mean anything about singularities, admittedly. But what we see through telescopes gives us a pretty strong hint that something like what we call black holes are out there.

i figured that, but tossed it out there anyways.
also it was a test to see if agent : orange was still kicking, and not dead from over work.

[GeorgieForPresident2216]

A to the O (that's for all you Annoying Orange fans.  No disrespect intended), maybe you can answer this question.  I've asked on places like 'ask an astronomer' but never got an answer that made sense to me.  Unfortunately I don't have a good grounding in general relativity, so I guess that's the problem.  This is to do with the formation of black holes. 

As a star collapses, my classical physics tells me any point outside of the star's shrinking radius will maintain a constant gravitational potential.  Therefore I don't think the the event horizon can be set up outside the star.  It must form within the collapsing star.  I've had that much confirmed.  Now, my understanding is that as matter and radiation approach the event horizon, the curvature of space becomes so great that they effectively approach light speed.  Consequently, anyone viewing the collapse must see time slow to a standstill as the star collapses into its own event horizon.

Wouldn't this mean the star would take the rest of eternity to collapse, and we would perpetually see it in a state of collapse -- never as a black hole?  Couldn't that also answer the question in the flawed study above of information not disappearing from our universe?

[wr250]

A to the O, maybe you can answer this question.  I've asked on places like 'ask an astronomer' but never got an answer that made sense to me.  Unfortunately I don't have a good grounding in general relativity, so I guess that's the problem.  This is to do with the formation of black holes. 

As a star collapses, my classical physics tells me any point outside of the star's shrinking radius will maintain a constant gravitational potential.  Therefore I don't think the the event horizon can be set up outside the star.  It must form within the collapsing star.  I've had that much confirmed.  Now, my understanding is that as matter and energy approach the event horizon, the curvature of space becomes so great that they effectively approach light speed.  Consequently, anyone viewing the collapse must see time slow to a standstill as the star collapses into its own event horizon.

Wouldn't this mean the star would take the rest of eternity to collapse, and we would perpetually see it in a state of collapse -- never as a black hole?

no it would slowly dim (and the collapse may appear slower?)  as fewer and fewer photons reach the observer (slowed by the gravity of the hole or is it in an ever expanding spiral around the hole until  the photon escapes the gravity well?) .at some point the quantity of photons would not be enough to detect, and the black hole becomes invisible. the matter around a black hole can be seen though as it displays the effects of circling the black hole in an accretion disk. not sure if answered the question or raised more questions.

however i have a question: could it be the number of galaxies may be much less than observed due to bending of light as it travels through  curved spacetime?
for example the following pic:
[attach=1]


in this case i used a star. the star on the right has its light bent around some massive object, and then appears (dimmer,redshifted, as the light traveled further) as another star above and to the left of the massive object.

[GeorgieForPresident2216]

no it would slowly dim (and the collapse may appear slower?)  as fewer and fewer photons reach the observer (slowed by the gravity of the hole or is it in an ever expanding spiral around the hole until  the photon escapes the gravity well?) .at some point the quantity of photons would not be enough to detect, and the black hole becomes invisible. the matter around a black hole can be seen though as it displays the effects of circling the black hole in an accretion disk. not sure if answered the question or raised more questions.

I considered that possibility, but not sure if that answers the question or not.  Would the luminosity ever completely die before reaching eternity?  And does that affect whether the star has collapsed or not?

however i have a question: could it be the number of galaxies may be much less than observed due to bending of light as it travels through  curved spacetime?
for example the following pic:

I'm not sure whether gravitational lensing could ever be that extreme even over the distance to the light horizon, but then again I'm not the one to answer.

[wr250]

I'm not sure whether gravitational lensing could ever be that extreme even over the distance to the light horizon, but then again I'm not the one to answer.

well i was thinking it was like when we "slingshot" a space probe around a planet.

[GeorgieForPresident2216]

well i was thinking it was like when we "slingshot" a space probe around a planet.

Maybe light from a distant galaxy passing near a black hole could do that.  Not sure if a sufficient amount of the light would be coherently redirected for us to notice the ghost image.  Hopefully Agent:  Orange makes another appearance .

[zeebo]

Oh well it was fun while it lasted. Guess we can all go back to looking forward to ending up in a singularity one day.

Jeez hope not, my apartment is cramped as it is.

[zeebo]

i figured that, but tossed it out there anyways.
also it was a test to see if agent : orange was still kicking, and not dead from over work.

Aha, and now we know how to get Agent's attention ... just float a story which implies Einstein was wrong.    

[area51drone]

Wouldn't it be great if astronomers found a fading star, so the "formation" of a black hole could be witnessed?    Maybe it's on wikipedia and I'm just too lazy at the moment to go looking, but how long does it take for the star to go from maximum brightness to disappearing?

[GeorgieForPresident2216]

Wouldn't it be great if astronomers found a fading star, so the "formation" of a black hole could be witnessed?    Maybe it's on wikipedia and I'm just too lazy at the moment to go looking, but how long does it take for the star to go from maximum brightness to disappearing?

I'm too lazy too.  I think the Supernova can be seen for a few days or weeks, but the remnants still remain luminous for millennia I would imagine.  Not sure about radiation from accretion disks.

[area51drone]

When I watched the Fillipenko series Understanding the Universe, he made a comment about black holes that I find intriguing... it was that a black hole exists everywhere, some time in your future.   I find that to be very profound, yet very puzzling.   

It's also true that for a photon travelling at the speed of light (obviously), it could exist everywhere - given that when it is emitted say, from a distant star, no time has passed for the photon between when it left and when it arrived at your eye.    I was watching another program tonight on quantum physics and of course they mentioned the double slit experiment which always gets me thinking.   I seem to recall reading Feynman's QED book (it was his lectures written in book form), that light has the possibility, through probability, to go in every direction before it reaches your eye.   I'm curious if anyone has ever created an experiment where even just one slit is behind the emitter.  Would it ever detect anything? 

If there is potential that light goes behind the source before it reaches your eye, would that mean that it would be detectable even, or does it mean that the light exists everywhere, and your interaction with the light by observing it says that it traveled in a straight line to you?

Off/on the subject - does anyone remember that Star Trek Voyager episode where Tom Paris goes past the warp barrier and exists everywhere?   

[DigitalPigSnuggler]

A to the O (that's for all you Annoying Orange fans.  No disrespect intended), maybe you can answer this question.  I've asked on places like 'ask an astronomer' but never got an answer that made sense to me.  Unfortunately I don't have a good grounding in general relativity, so I guess that's the problem.  This is to do with the formation of black holes. 

As a star collapses, my classical physics tells me any point outside of the star's shrinking radius will maintain a constant gravitational potential.  Therefore I don't think the the event horizon can be set up outside the star.  It must form within the collapsing star.  I've had that much confirmed.  Now, my understanding is that as matter and radiation approach the event horizon, the curvature of space becomes so great that they effectively approach light speed.  Consequently, anyone viewing the collapse must see time slow to a standstill as the star collapses into its own event horizon.

Wouldn't this mean the star would take the rest of eternity to collapse, and we would perpetually see it in a state of collapse -- never as a black hole?  Couldn't that also answer the question in the flawed study above of information not disappearing from our universe?

I can give you the wrong answer for now, and AO can correct it on his next visit.

To an outside observer at a fixed point, the actions of matter falling into a black hole seem to slow down.  To cite a classic example, if you threw a clock in there, it would appear to tick slower and slower as it approaches the event horizon.   It would also appear to move slower and slower, eventually taking an infinite amount of time to reach the event horizon.  At the same time, the object would appear to become redder and dimmer, due to gravitational effects.  At the point just before it reaches the event horizon, the object becomes so dim that it can no longer be seen.

For that reason, an outside observer of a collapsing star would see a dim image of the star's surface "frozen" in position as it reaches the event horizon.

Wouldn't this mean the star would take the rest of eternity to collapse, and we would perpetually see it in a state of collapse -- never as a black hole?

The star would not take the rest of eternity to collapse.  To an outside observer, the collapse would appear to move slower and slower until it essentially freezes in place.  However, the observer would not see that image perpetually.  S/he would observe the process of the collapse move more and more slowly, and become redder and dimmer, until it disappeared.  And we can't by definition observe a black hole (hence the name) in any case.  To emphasize the point, this is what the observer sees, not what is taking place with the star itself.

[DigitalPigSnuggler]

When I watched the Fillipenko series Understanding the Universe, he made a comment about black holes that I find intriguing... it was that a black hole exists everywhere, some time in your future.   I find that to be very profound, yet very puzzling. 

This sounds like a perversion of the sum over histories theory, if I'm interpreting it correctly.  It seems to imply that because something could be anywhere, that eventually it will be everywhere.  That's certainly not the case within a human being's lifetime.  I'm not sure it applies to black holes, either, which are strange little critters.

[wr250]

This sounds like a perversion of the sum over histories theory, if I'm interpreting it correctly.  It seems to imply that because something could be anywhere, that eventually it will be everywhere.  That's certainly not the case within a human being's lifetime.  I'm not sure it applies to black holes, either, which are strange little critters.

was not the entire observable universe once condensed into a single point (a black hole?)  which then erupted for reasons unknown? .therefore black hole was at one time, everywhere.

[GeorgieForPresident2216]

I can give you the wrong answer for now, and AO can correct it on his next visit.

To an outside observer at a fixed point, the actions of matter falling into a black hole seem to slow down.  To cite a classic example, if you threw a clock in there, it would appear to tick slower and slower as it approaches the event horizon.   It would also appear to move slower and slower, eventually taking an infinite amount of time to reach the event horizon.  At the same time, the object would appear to become redder and dimmer, due to gravitational effects.  At the point just before it reaches the event horizon, the object becomes so dim that it can no longer be seen.

For that reason, an outside observer of a collapsing star would see a dim image of the star's surface "frozen" in position as it reaches the event horizon.

The star would not take the rest of eternity to collapse.  To an outside observer, the collapse would appear to move slower and slower until it essentially freezes in place.  However, the observer would not see that image perpetually.  S/he would observe the process of the collapse move more and more slowly, and become redder and dimmer, until it disappeared.  And we can't by definition observe a black hole (hence the name) in any case.  To emphasize the point, this is what the observer sees, not what is taking place with the star itself.

That's a good point about the red shift.  I didn't think about that.

Okay, so we would see the process effectively frozen but for the star it would be over in an instant.  Is this a case where, if there could be an observer on the event horizon, he would see the reverse.. things happening normally for him but the rest of the universe nearly frozen?  And from our point of view does it matter that we have different perspectives?.. I mean for us the star is still effectively frozen, the black hole isn't fully forming, and no information is being lost from the universe. 

I don't know, I'm still confused.  Thank you for trying to explain it.

[GeorgieForPresident2216]

was not the entire observable universe once condensed into a single point (a black hole?)  which then erupted for reasons unknown? .therefore black hole was at one time, everywhere.

One possibility is that everything started as a singularity, but the Big Bang Theory doesn't stipulate that... all we know for sure is that everything has expanded.. to quote a popular television program.. from a hot, dense state.

[DigitalPigSnuggler]

was not the entire observable universe once condensed into a single point (a black hole?)

If the entire universe was squeezed into a singularity, then where was the hole?

Also:

therefore black hole was at one time, everywhere.

it was that a black hole exists everywhere, some time in your future.   

The person cited was speaking about the future, not the past.

[DigitalPigSnuggler]

Is this a case where, if there could be an observer on the event horizon, he would see the reverse.. things happening normally for him but the rest of the universe nearly frozen? 

Someone traveling into a black hole would not be aware that he had crossed the event horizon.  For him, everything around him would behave as before crossing that line.  At this point, though, his fate is sealed.  He is doomed to be pulled into a long noodle and then pulled apart, his mass accreted by the singularity.  But before that gruesome end, he would see the progress of the universe moving faster and faster into the future.  So quickly that there would be no time to analyze it.  It would be a very exciting way to die, though.

And from our point of view does it matter that we have different perspectives?.. I mean for us the star is still effectively frozen, the black hole isn't fully forming, and no information is being lost from the universe. 

That's not exactly how it works.  We see the star in motion until it slows down to the point that it appears to have stopped.  That image fades out, but the formation of the black hole continues, out of our observation.  The star disappears, and now there is a black hole.  Or so goes the theory.  Since we can't observe a black hole directly, there's often a disclaimer of the type outlined by AO above: it's either a black hole, or something different that behaves like a black hole in all of the ways that we can observe.

[GeorgieForPresident2216]

Someone traveling into a black hole would not be aware that he had crossed the event horizon.  For him, everything around him would behave as before crossing that line.  At this point, though, his fate is sealed.  He is doomed to be pulled into a long noodle and then pulled apart, his mass accreted by the singularity.  But before that gruesome end, he would see the progress of the universe moving faster and faster into the future.  So quickly that there would be no time to analyze it.  It would be a very exciting way to die, though...

Right, because he's in the accelerating reference frame.  Okay, still mulling this over.  Thanks.

[Tarbaby]

A star could collapse into a black hole within seconds. At least that's what Siri just told me. But she was asking me questions about that clock, was it a windup clock or was it running on a battery?