“Humanity has won its battle. Liberty now has a country.” -Marquis de Lafayette
There’s so much science to talk about in any given week here at Starts With A Bang! It’s sometimes hard to choose, but one particular topic stole the show this past week: black holes. Sure, we took on other things, too, but we didn’t even talk all that much about the biggest discovery of all: LIGO’s direct detection of a third pair of merging black holes! If you had doubts after one, and they were allayed after two, then three should hammer home that these are real, robust and common. There are a lot of nuances to talk about, so expect more ahead! In the meantime, here’s a look back at the past week of stories:
- What does the edge of the Universe look like? (for Ask Ethan),
- Surprise! The Universe has a third way to form black holes (for Mostly Mute Monday),
- Is there really a cosmological constant? Or is dark energy changing with time? (an interesting look at a cosmic mismatch, by Sabine Hossenfelder),
- Nothing escapes from a black hole, and now astronomers have proof,
- Break the Standard Model? An ultra-rare decay threatens to do what the LHC can’t, and
- What will the death of the Milky Way look like?
That was all my say, of course. What about yours? Let’s dive in to what you had to add — and what I can help out by clarifying, adding or delivering some bonus science to — on this edition of our comments of the week!
Tweets from Evergreen State College and Professor Weinstein tell two very different stories.
From Denier on some disturbing political trends: “Please be careful with even handed statements like that. In your profession, especially in the Pacific Northwest, adopting a position any less screechy than outright vilification to paint the center and right as jackbooted Nazis can end your career. I’m sure you’re familiar with the Bernie-voting Biology Professor teaching about 2 hours up the road from you who dared to blaspheme by stating that it was wrong to discriminate based on skin color, and now is in fear for his life because students have labeled him as “anti-black”.”
It’s important to remember that no matter where you are on the political spectrum, there are going to be people forgetting the cardinal rule to freedoms of all types: your freedoms end when they infringe upon another’s. Your freedom of anything — of speech, of right to own property, to punch the air in front of your face — end where another person’s freedom, autonomy, right to exist, etc., begin. You don’t get to banish someone from your campus, your city or your country because of their race, religion, perspectives or even their bigotry.
That said, less than two hours up the road from me, there are actual jackbooted Nazis marching today to spread a pro-Nazi message of fear, oppression, persecution and violence. I hope you are at least as vocal in your opposition of that as you are in your opposition to the students’ treatment of Professor Weinstein.
The three valence quarks of a proton contribute to its spin, but so do the gluons, sea quarks and antiquarks, and orbital angular momentum as well. Image credit: APS/Alan Stonebraker.
From Elle H.C. on sea quarks: “The waves that the wings of a helicopter make are not wings, they are waves, even if these waves can ‘hit’ you hard.
So it does not seem correct to talk about the multitude of possible quark-formations.”
No, deep inelastic scattering tells you what you actually hit. You can tell what the mass, charge, and even the lepton/baryon family is of the particle you hit. In your helicopter analogy, you don’t hit wings or waves; you hit particles. Those may be helicopter blade particles, they may be air particles, they may be particles of other material in the air, but they are particles. Inside the proton, you can hit valence quarks, sea quarks, or gluons, and you can tell them apart. I am less interested in what seems correct to you than what the experimental data indicates. You can know.
Image credit: SpaceX / Elon Musk.
From eric on Mars plans: “I would think that a natural intermediate step would be to land automated heavy construction vehicles on the planet. Use them to build pits, walls, underground tunnels, etc. If you can’t safely land them, then you can’t safely land humans that would require the same tonnage. And if you can land them, then you should land them months or years before the humans arrive anyway, so that some basic environmental protection structures are already in place when the humans arrive.”
We can always argue over how far we should go in an automated fashion before we send humans. I agree with you about some of these things. I would like to see us land heavy payloads softly, safely, accurately, and repeatably on Mars before we land crewed spacecraft there. But as far as having the protection structures already in place? I don’t think that’s necessary, particularly if it’s easier to construct them with trained astronauts in situ than with a fully robotic/remote approach.
But no, I don’t think we’re far off from one another here, either.
Image credit: Mars One / Bryan Versteeg.
And from Sean T on what to fear if we fail: “You are absolutely correct: to accomplish the goal, an attempt must be made. I just fear that a single attempt may be all that we get, and that an expensive failure might well make a further attempt impossible politically.”
Whenever we encounter setbacks, we have two ways to respond: to redouble our efforts and try again, or to give up out of fear and frustration. Believe it or not, I believe this is entirely a marketing problem, not a scientific one. If we can sell the idea of humans on Mars as something that’s valuable enough, we’ll go again even if we fail the first time… or the first few times. But we shall see.
From Narad on the Forbes not working problem: “I’m loathe to invoke this site, as the denizens generally have no idea what they’re talking about (e.g., the “solution” to everything always involves “repair permissions”), but the Forbes problem is not unknown.”
It looks like this is a problem that occurred with some recent updates to both Forbes and Safari. Yes, there is probably a fundamental problem at play, and Forbes is exactly as committed to solving it as you’d expect. (They’re aware of it, and that’s the information I got.) If you can, use Chrome or Firefox, and things should load up just fine.
Artist’s impression of a black hole. What goes on outside the black hole is well understood, but inside, we run up against the limits of fundamental physics… and potentially, the laws governing the Universe itself. Image credit: XMM-Newton, ESA, NASA.
From fred on what happens inside an event horizon: “Is it necessary that once escape velocity exceeds the speed of light that whatever lies behind the curtain must be a singularity as predicted by the maths?”
Only if all of physics is correct. If particles cannot be exchanged faster than the speed of light, then there would be no way to exert an “outward” force on anything inside the event horizon. And if you can’t exert an outward force, there is no way to fight gravitational collapse down to a singularity. So it’s only “necessary” to form a singularity if we take our current understanding of fundamental particle physics as correct. Of course, whether a “singularity” is actually something else in nature would require quantum gravity, but the “hard, solid object made of particles” interpretation has this problem regardless of quantum gravity.
Artist’s logarithmic scale conception of the observable universe. Galaxies give way to large-scale structure and the hot, dense plasma of the Big Bang at the outskirts. This ‘edge’ is a boundary only in time. Image credit: Wikipedia user Pablo Carlos Budassi.
From PJ on what the edge of the Universe looks like: “Nicely & simply laid out, Ethan.”
Thank you. I like the idea of an edge in time; after all, time is a dimension too. It seems like there’s an incredible science fiction story in that idea… both in the past and in the future.
By the way, I thought I’d drop a little teaser for all of you here: you know that my first book, Beyond The Galaxy, is available everywhere (and up to 4.8 stars on Amazon), and that my second book, Treknology, is coming out in October and can be pre-ordered today. But what you haven’t heard is that I’m currently planning my third book now (and yes, there’s an idea for the fourth in the works, too), and it’s going to be my first attempt at writing a book with no pictures. (To keep costs as low as possible, ostensibly.) I’m currently shopping agents for it, as it’s a very different type of book, so if you have any recommendations, feel free to reach out!
The visible/near-IR photos from Hubble show a massive star, about 25 times the mass of the Sun, that has winked out of existence, with no supernova or other explanation. Direct collapse is the only reasonable candidate explanation. Image credit: NASA/ESA/C. Kochanek (tOSU).
From anneb on direct collapse black holes: “From the article, direct collapse is described as very plausible. However, during the collapse of the gas cloud, there must be a phase where nuclear fusion ignites a star.”
Be very careful with words like ‘must’ in this context. For cases where you have objects under, say, a few hundred solar masses, yes, you will form a star where nuclear fusion ignites. That star may then undergo a variety of cataclysmic events that form a black hole, not all of which will result in a supernova. I’d be curious to learn if a “supernova impostor,” like the type of event Eta Carinae underwent, could give rise to a black hole; perhaps in the next few hundred or thousand years, Eta Carinae itself will get another chance!
But in the case of much larger objects, you may not need fusion at all to get a direct collapse black hole. I don’t think it’s a necessary assumption, and I don’t think anyone knows where the mass threshold is. But I wouldn’t rule it out entirely, not just yet.
Although we’ve seen black holes directly merging three separate times in the Universe, we know many more exist. Image credit: LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet).
From John on direct collapse and gravitational waves: “If the hypothesized direct collapse also left a distinct gravity wave signature that current and/or planned instruments could record, that would provide additional, independent corroboration.”
I wish that were a good plan. Unfortunately, if you want to create a large-amplitude signal, you need a large mass moving rapidly through a rapidly changing gravitational field. The spherically symmetric nature of direct collapse makes that virtually impossible, and hence gravitational wave signatures from an event like this are expected to be very small in magnitude. (This is expected to be the case for supernovae, too.) However, neutron star “quakes,” which correspond to pulsar timing “glitches,” could be an example of a short-period transient signal that shows up in gravitational waves. The next generation of LIGO-like detectors might get there.
Additional details of interest provided by Michael Kelsey: “However, a spherically symmetric which undergoes an asymmetric explosion (i.e., one with a quadrupole moment) can generate gravitational waves.
In fact, one of LIGO’s search targets are the supernovae believed responsible for gamma-ray bursts, because the favored model of those involves a residual toroidal accretion disk which could have a sufficiently large quadrupole moment to emit GW.”
The history of the Universe tells the story of a race between gravitation and expansion, until about six billion years ago, when dark energy becomes important. Image credit: NASA / GSFC.
From Frank on dark energy and energy conservation: “I think Dark Energy keeps increasing or even staying constant goes against conservation of energy/information because unit volume of spacetime must have constant amount of zero-point energy.”
It’s difficult to remember that in General Relativity, not only is global energy not conserved, it isn’t defined. We can ad hoc a definition, as Sinisa Lazarek reminds us that I and Sean Carroll have pointed out, but that is not robustly true. If you must think of energy conservation for the Universe, you would do well to remember the Work-Energy theorem, and that Work is the “dot product” of a Force and a Distance. If you push outwards — in the same direction — as an expanding object, you do positive work; if you pull inwards — in the opposite direction — as an expanding object, you do negative work.
Your comment indicates that you have no problem with that second option for the Universe: the expansion is outward, gravity pulls inwards, and you do negative work on the expanding Universe. But what if the sign is reversed? Is energy conservation any less good? No. My point is that all of the viable options for dark energy are still valid, and your local notions of energy conservation are insufficient for restricting the physical options for global properties of dark energy. It could still increase or decrease in strength, but the evidence favors a constant value.
Against a seemingly eternal backdrop of everlasting darkness, a single flash of light will emerge: the evaporation of the final black hole in the Universe. Image credit: ortega-pictures / Pixabay.
From John on escaping a black hole: ““Nothing Escapes From A Black Hole, And Now Astronomers Have Proof”
Not even information?”
I had no idea that my title for this article — which is about how an object getting swallowed by the event horizon doesn’t have anything spit out again from inside on observable timescales — would cause so many people to go 10^70-something years in the future and worry about black hole decay! I re-read the article and I don’t think there’s any ambiguity, so to clarify, on long enough timescales, black holes do decay away entirely, but that is still not anything (matter or energy) crossing from inside the horizon to outside.
If event horizons are real, then a star falling into a central black hole would simply be devoured, leaving no trace of the encounter behind. (If not, there would be some radical emissions outside the horizon with a ‘splat’.) Image credit: Mark A. Garlick/CfA.
From Michael Kelsey on what was constrained, and how: “If black holes “don’t exist” (i.e., if there is some other simple compact object, like a super duper neutron star, which can provide the necessary gravitating mass in a small space), then there should/would be evidence for a surface of emission from such a compact object.”
The alternative to an event horizon, which requires modifying General Relativity, would be a hard-surface at a radius greater than the radius of a predicted event horizon. The lack of evidence from Pan-STARRS indicates that the hard surface idea is heavily disfavored.
Image credit: KECK / UCLA Galactic Center Group / Andrea Ghez et al.
From Paul Dekous on the possibility that a black hole is not mass: “If a Galaxy is like a school of fish that swims around in loops, stirring up SpaceTime, than at the center of that whirlpool the friction and compression is the most intense, the distance between the top side going in the opposite direction of the bottom side is the smallest.”
That’s a cute analogy, but that’s not what we observe. If anything like what you were describing were happening to space, then the orbits of stars would be perturbed from this classical, Keplerian path in a way other than classical GR predicts (i.e., precession of the perihelion of the orbits). There’s a mass there, which theory and observation agree on, for our black hole and for many others.
In other words, we can rule out your idea.
From Michael Mooney on my self-contradictions: “The last reversal/ contradiction (from evaporating black holes to Friday’s headline) took 10 days. The switch only took two days this time. The rate of change Ethan’s opinion on black holes is accelerating!”
I have been writing about science on the internet for nearly ten years now, and one of the extraordinary lessons I’ve learned is there is nothing I can state, no matter how clearly, how supported by evidence, or how universally-agreed-upon, that won’t result in me being told I’m wrong — and, quite often, how awful I am in addition — by someone. So what can I say to everyone who’s done this?
The Milky Way, as we know it today, hasn’t changed much in billions of years. But give it enough time, and eventually everything will disappear. Image credit: ESO/S. Guisard.
I see you. I recognize that you’re doing your best to understand the world and Universe around you, and that sometimes you run into aspects of it that are challenging. Not only challenging to understand, but sometimes challenging to your own self-identity. The Universe gives us many difficult aspects to grapple with, and we don’t always succeed at putting them into sensible order in our minds.
Well, don’t give up. Keep trying. Keep challenging yourself, because that’s what being alive is. Until it’s time to die — and that time is not yet here — there’s always more to learn, for all of us. Good luck on your journey, and I’ll be here to share it with you if you still want to come along with me.
from ScienceBlogs http://ift.tt/2s7g7BS
“Humanity has won its battle. Liberty now has a country.” -Marquis de Lafayette
There’s so much science to talk about in any given week here at Starts With A Bang! It’s sometimes hard to choose, but one particular topic stole the show this past week: black holes. Sure, we took on other things, too, but we didn’t even talk all that much about the biggest discovery of all: LIGO’s direct detection of a third pair of merging black holes! If you had doubts after one, and they were allayed after two, then three should hammer home that these are real, robust and common. There are a lot of nuances to talk about, so expect more ahead! In the meantime, here’s a look back at the past week of stories:
- What does the edge of the Universe look like? (for Ask Ethan),
- Surprise! The Universe has a third way to form black holes (for Mostly Mute Monday),
- Is there really a cosmological constant? Or is dark energy changing with time? (an interesting look at a cosmic mismatch, by Sabine Hossenfelder),
- Nothing escapes from a black hole, and now astronomers have proof,
- Break the Standard Model? An ultra-rare decay threatens to do what the LHC can’t, and
- What will the death of the Milky Way look like?
That was all my say, of course. What about yours? Let’s dive in to what you had to add — and what I can help out by clarifying, adding or delivering some bonus science to — on this edition of our comments of the week!
Tweets from Evergreen State College and Professor Weinstein tell two very different stories.
From Denier on some disturbing political trends: “Please be careful with even handed statements like that. In your profession, especially in the Pacific Northwest, adopting a position any less screechy than outright vilification to paint the center and right as jackbooted Nazis can end your career. I’m sure you’re familiar with the Bernie-voting Biology Professor teaching about 2 hours up the road from you who dared to blaspheme by stating that it was wrong to discriminate based on skin color, and now is in fear for his life because students have labeled him as “anti-black”.”
It’s important to remember that no matter where you are on the political spectrum, there are going to be people forgetting the cardinal rule to freedoms of all types: your freedoms end when they infringe upon another’s. Your freedom of anything — of speech, of right to own property, to punch the air in front of your face — end where another person’s freedom, autonomy, right to exist, etc., begin. You don’t get to banish someone from your campus, your city or your country because of their race, religion, perspectives or even their bigotry.
That said, less than two hours up the road from me, there are actual jackbooted Nazis marching today to spread a pro-Nazi message of fear, oppression, persecution and violence. I hope you are at least as vocal in your opposition of that as you are in your opposition to the students’ treatment of Professor Weinstein.
The three valence quarks of a proton contribute to its spin, but so do the gluons, sea quarks and antiquarks, and orbital angular momentum as well. Image credit: APS/Alan Stonebraker.
From Elle H.C. on sea quarks: “The waves that the wings of a helicopter make are not wings, they are waves, even if these waves can ‘hit’ you hard.
So it does not seem correct to talk about the multitude of possible quark-formations.”
No, deep inelastic scattering tells you what you actually hit. You can tell what the mass, charge, and even the lepton/baryon family is of the particle you hit. In your helicopter analogy, you don’t hit wings or waves; you hit particles. Those may be helicopter blade particles, they may be air particles, they may be particles of other material in the air, but they are particles. Inside the proton, you can hit valence quarks, sea quarks, or gluons, and you can tell them apart. I am less interested in what seems correct to you than what the experimental data indicates. You can know.
Image credit: SpaceX / Elon Musk.
From eric on Mars plans: “I would think that a natural intermediate step would be to land automated heavy construction vehicles on the planet. Use them to build pits, walls, underground tunnels, etc. If you can’t safely land them, then you can’t safely land humans that would require the same tonnage. And if you can land them, then you should land them months or years before the humans arrive anyway, so that some basic environmental protection structures are already in place when the humans arrive.”
We can always argue over how far we should go in an automated fashion before we send humans. I agree with you about some of these things. I would like to see us land heavy payloads softly, safely, accurately, and repeatably on Mars before we land crewed spacecraft there. But as far as having the protection structures already in place? I don’t think that’s necessary, particularly if it’s easier to construct them with trained astronauts in situ than with a fully robotic/remote approach.
But no, I don’t think we’re far off from one another here, either.
Image credit: Mars One / Bryan Versteeg.
And from Sean T on what to fear if we fail: “You are absolutely correct: to accomplish the goal, an attempt must be made. I just fear that a single attempt may be all that we get, and that an expensive failure might well make a further attempt impossible politically.”
Whenever we encounter setbacks, we have two ways to respond: to redouble our efforts and try again, or to give up out of fear and frustration. Believe it or not, I believe this is entirely a marketing problem, not a scientific one. If we can sell the idea of humans on Mars as something that’s valuable enough, we’ll go again even if we fail the first time… or the first few times. But we shall see.
From Narad on the Forbes not working problem: “I’m loathe to invoke this site, as the denizens generally have no idea what they’re talking about (e.g., the “solution” to everything always involves “repair permissions”), but the Forbes problem is not unknown.”
It looks like this is a problem that occurred with some recent updates to both Forbes and Safari. Yes, there is probably a fundamental problem at play, and Forbes is exactly as committed to solving it as you’d expect. (They’re aware of it, and that’s the information I got.) If you can, use Chrome or Firefox, and things should load up just fine.
Artist’s impression of a black hole. What goes on outside the black hole is well understood, but inside, we run up against the limits of fundamental physics… and potentially, the laws governing the Universe itself. Image credit: XMM-Newton, ESA, NASA.
From fred on what happens inside an event horizon: “Is it necessary that once escape velocity exceeds the speed of light that whatever lies behind the curtain must be a singularity as predicted by the maths?”
Only if all of physics is correct. If particles cannot be exchanged faster than the speed of light, then there would be no way to exert an “outward” force on anything inside the event horizon. And if you can’t exert an outward force, there is no way to fight gravitational collapse down to a singularity. So it’s only “necessary” to form a singularity if we take our current understanding of fundamental particle physics as correct. Of course, whether a “singularity” is actually something else in nature would require quantum gravity, but the “hard, solid object made of particles” interpretation has this problem regardless of quantum gravity.
Artist’s logarithmic scale conception of the observable universe. Galaxies give way to large-scale structure and the hot, dense plasma of the Big Bang at the outskirts. This ‘edge’ is a boundary only in time. Image credit: Wikipedia user Pablo Carlos Budassi.
From PJ on what the edge of the Universe looks like: “Nicely & simply laid out, Ethan.”
Thank you. I like the idea of an edge in time; after all, time is a dimension too. It seems like there’s an incredible science fiction story in that idea… both in the past and in the future.
By the way, I thought I’d drop a little teaser for all of you here: you know that my first book, Beyond The Galaxy, is available everywhere (and up to 4.8 stars on Amazon), and that my second book, Treknology, is coming out in October and can be pre-ordered today. But what you haven’t heard is that I’m currently planning my third book now (and yes, there’s an idea for the fourth in the works, too), and it’s going to be my first attempt at writing a book with no pictures. (To keep costs as low as possible, ostensibly.) I’m currently shopping agents for it, as it’s a very different type of book, so if you have any recommendations, feel free to reach out!
The visible/near-IR photos from Hubble show a massive star, about 25 times the mass of the Sun, that has winked out of existence, with no supernova or other explanation. Direct collapse is the only reasonable candidate explanation. Image credit: NASA/ESA/C. Kochanek (tOSU).
From anneb on direct collapse black holes: “From the article, direct collapse is described as very plausible. However, during the collapse of the gas cloud, there must be a phase where nuclear fusion ignites a star.”
Be very careful with words like ‘must’ in this context. For cases where you have objects under, say, a few hundred solar masses, yes, you will form a star where nuclear fusion ignites. That star may then undergo a variety of cataclysmic events that form a black hole, not all of which will result in a supernova. I’d be curious to learn if a “supernova impostor,” like the type of event Eta Carinae underwent, could give rise to a black hole; perhaps in the next few hundred or thousand years, Eta Carinae itself will get another chance!
But in the case of much larger objects, you may not need fusion at all to get a direct collapse black hole. I don’t think it’s a necessary assumption, and I don’t think anyone knows where the mass threshold is. But I wouldn’t rule it out entirely, not just yet.
Although we’ve seen black holes directly merging three separate times in the Universe, we know many more exist. Image credit: LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet).
From John on direct collapse and gravitational waves: “If the hypothesized direct collapse also left a distinct gravity wave signature that current and/or planned instruments could record, that would provide additional, independent corroboration.”
I wish that were a good plan. Unfortunately, if you want to create a large-amplitude signal, you need a large mass moving rapidly through a rapidly changing gravitational field. The spherically symmetric nature of direct collapse makes that virtually impossible, and hence gravitational wave signatures from an event like this are expected to be very small in magnitude. (This is expected to be the case for supernovae, too.) However, neutron star “quakes,” which correspond to pulsar timing “glitches,” could be an example of a short-period transient signal that shows up in gravitational waves. The next generation of LIGO-like detectors might get there.
Additional details of interest provided by Michael Kelsey: “However, a spherically symmetric which undergoes an asymmetric explosion (i.e., one with a quadrupole moment) can generate gravitational waves.
In fact, one of LIGO’s search targets are the supernovae believed responsible for gamma-ray bursts, because the favored model of those involves a residual toroidal accretion disk which could have a sufficiently large quadrupole moment to emit GW.”
The history of the Universe tells the story of a race between gravitation and expansion, until about six billion years ago, when dark energy becomes important. Image credit: NASA / GSFC.
From Frank on dark energy and energy conservation: “I think Dark Energy keeps increasing or even staying constant goes against conservation of energy/information because unit volume of spacetime must have constant amount of zero-point energy.”
It’s difficult to remember that in General Relativity, not only is global energy not conserved, it isn’t defined. We can ad hoc a definition, as Sinisa Lazarek reminds us that I and Sean Carroll have pointed out, but that is not robustly true. If you must think of energy conservation for the Universe, you would do well to remember the Work-Energy theorem, and that Work is the “dot product” of a Force and a Distance. If you push outwards — in the same direction — as an expanding object, you do positive work; if you pull inwards — in the opposite direction — as an expanding object, you do negative work.
Your comment indicates that you have no problem with that second option for the Universe: the expansion is outward, gravity pulls inwards, and you do negative work on the expanding Universe. But what if the sign is reversed? Is energy conservation any less good? No. My point is that all of the viable options for dark energy are still valid, and your local notions of energy conservation are insufficient for restricting the physical options for global properties of dark energy. It could still increase or decrease in strength, but the evidence favors a constant value.
Against a seemingly eternal backdrop of everlasting darkness, a single flash of light will emerge: the evaporation of the final black hole in the Universe. Image credit: ortega-pictures / Pixabay.
From John on escaping a black hole: ““Nothing Escapes From A Black Hole, And Now Astronomers Have Proof”
Not even information?”
I had no idea that my title for this article — which is about how an object getting swallowed by the event horizon doesn’t have anything spit out again from inside on observable timescales — would cause so many people to go 10^70-something years in the future and worry about black hole decay! I re-read the article and I don’t think there’s any ambiguity, so to clarify, on long enough timescales, black holes do decay away entirely, but that is still not anything (matter or energy) crossing from inside the horizon to outside.
If event horizons are real, then a star falling into a central black hole would simply be devoured, leaving no trace of the encounter behind. (If not, there would be some radical emissions outside the horizon with a ‘splat’.) Image credit: Mark A. Garlick/CfA.
From Michael Kelsey on what was constrained, and how: “If black holes “don’t exist” (i.e., if there is some other simple compact object, like a super duper neutron star, which can provide the necessary gravitating mass in a small space), then there should/would be evidence for a surface of emission from such a compact object.”
The alternative to an event horizon, which requires modifying General Relativity, would be a hard-surface at a radius greater than the radius of a predicted event horizon. The lack of evidence from Pan-STARRS indicates that the hard surface idea is heavily disfavored.
Image credit: KECK / UCLA Galactic Center Group / Andrea Ghez et al.
From Paul Dekous on the possibility that a black hole is not mass: “If a Galaxy is like a school of fish that swims around in loops, stirring up SpaceTime, than at the center of that whirlpool the friction and compression is the most intense, the distance between the top side going in the opposite direction of the bottom side is the smallest.”
That’s a cute analogy, but that’s not what we observe. If anything like what you were describing were happening to space, then the orbits of stars would be perturbed from this classical, Keplerian path in a way other than classical GR predicts (i.e., precession of the perihelion of the orbits). There’s a mass there, which theory and observation agree on, for our black hole and for many others.
In other words, we can rule out your idea.
From Michael Mooney on my self-contradictions: “The last reversal/ contradiction (from evaporating black holes to Friday’s headline) took 10 days. The switch only took two days this time. The rate of change Ethan’s opinion on black holes is accelerating!”
I have been writing about science on the internet for nearly ten years now, and one of the extraordinary lessons I’ve learned is there is nothing I can state, no matter how clearly, how supported by evidence, or how universally-agreed-upon, that won’t result in me being told I’m wrong — and, quite often, how awful I am in addition — by someone. So what can I say to everyone who’s done this?
The Milky Way, as we know it today, hasn’t changed much in billions of years. But give it enough time, and eventually everything will disappear. Image credit: ESO/S. Guisard.
I see you. I recognize that you’re doing your best to understand the world and Universe around you, and that sometimes you run into aspects of it that are challenging. Not only challenging to understand, but sometimes challenging to your own self-identity. The Universe gives us many difficult aspects to grapple with, and we don’t always succeed at putting them into sensible order in our minds.
Well, don’t give up. Keep trying. Keep challenging yourself, because that’s what being alive is. Until it’s time to die — and that time is not yet here — there’s always more to learn, for all of us. Good luck on your journey, and I’ll be here to share it with you if you still want to come along with me.
from ScienceBlogs http://ift.tt/2s7g7BS
, who is well known to all the readers of this blog. This is all connected in an interesting way, which I will write about some time (I don’t think Rebecca or Shawn are aware of that connection, now that I think about it).
was $15 is now $10.20. (See 
by Krauss, was $27, now $14.16.
by Neil deGrasse Tyson and others, was $39.95, now 26.74.
was $29.95, now $13.36.