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Physics and astronomy thread (1 Viewer)

wilked said:
Reminder:

The Farthest is streaming free for the next week or so

http://www.pbs.org/the-farthest/home/

tells the the story of the Voyager. Great movie 
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Watched this tonight. Thank you for the recommendation. Really enjoyed it, and it brought back memories of '79 reading National Geographic with the amazing new photos of Jupiter. 

ETA : I also loved seeing the clothes the scientists were wearing in the late 70's and early 80's.

 
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jamny said:
Wow! 1st Interstellar Asteroid Is a Spinning Space Cigar
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This visitor from beyond our solar system will be probed for signs of life

Some scientists, though they are swift to say 'Oumuamua is probably natural, have not yet ruled out more extraordinary origins. “The possibility that this object is, in fact, an artificial object — that it is a spaceship, essentially — is a remote possibility,” Andrew Siemion, director of the Berkeley Search for Extraterrestrial Intelligence Research Center, told The Washington Post on Monday.
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msommer said:
This visitor from beyond our solar system will be probed

msommer said:
This visitor from beyond our solar system will be probed for signs of life
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for signs of life
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I thought the probing was happening the last couple days? pretty sure I saw something pop up this morning that nothing had been found yet... and they're running out of time as it speeds away from us. 

also thought the bump today would be about the 8th exo-planet found in the kepler-90 system, a record number (and matching us).

they used AI (google guy involved) to harvest more data from older kepler data- and so skynet begins.

 
El Floppo said:
I thought the probing was happening the last couple days? pretty sure I saw something pop up this morning that nothing had been found yet... and they're running out of time as it speeds away from us. 
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There's ice, but probably not aliens

He added: "It's entirely consistent with cometary bodies we've studied - with the Rosetta probe, for example - in our own Solar System."

Co-author Dr Michele Bannister, also from QUB, commented: "We've discovered that this is a planetesimal with a well-baked crust that looks a lot like the tiniest worlds in the outer regions of our Solar System, has a greyish/red surface and is highly elongated, probably about the size and shape of the Gherkin skyscraper in London.

"It's fascinating that the first interstellar object discovered looks so much like a tiny world from our own home system. This suggests that the way our planets and asteroids formed has a lot of kinship to the systems around other stars."
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"All the data we have at the moment turn out to be consistent with what we might expect from an object ejected by another star," he said.
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The recent NOVA on Black Holes was excellent and, for those who might not have noticed, the series How the Universe Works has new episodes with a 2 hour episode on Black Holes to start out.

The NOVA special cleared up a bunch of questions but as usual, brought up some more. I can grasp the idea of a black hole warping spacetime and that anything that passes the event horizon cannot escape but I get confused when it is depicted like this. Much like how they depict any warping of spacetime.

Questions:

Is that photo a literal depiction of the concept of bending of spacetime? Does it always go downward? If you fly along the southern point of a planet, wouldn't you then be pushed away?

In the black hole, are you not sucked into an actual spherical black hole or is it into the extreme bending of spacetime?

A couple of other things. I don't get how certain the people at LIGO are that the gravitational waves came from colliding black holes. And I loved hearing Mike Rowe say Hairy Black Hole.

 
Walking Boot said:
Well, OK, it's not quite like that. That's what it looks like in 2 dimensions. Now, imagine that that funnel is like that no matter what way you look at it. From every angle, it does that. I know, it seems off, but, black holes are weird, man. 

But for simplicity's sake, if you were in a spaceship approaching a black hole, you would just think of it that way because from whatever angle you're approaching it, that's how it looks, pulling stuff toward a center point. From whatever angle you came at it, it's like you're going straight down the funnel from due north to due south.
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See, that makes more sense to me and the depictions just confused me more as if the universe is on a flat plane and spacetime was bent in a particular direction.

 
badmojo1006 said:
Watching NOVA tonight about Black Holes. Interesting, but I  :wub: the host Janna Levin
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At first I was like  "she's ok" but she got hotter and hotter as the show went on. Great body and looks like a real nice rack. Loved the heavy chain necklace..

 
jamny said:
See, that makes more sense to me and the depictions just confused me more as if the universe is on a flat plane and spacetime was bent in a particular direction.
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It is very difficult (impossible?) to produce an image that allows us to fully conceptualize the geometry of space around a mass, and even more difficult when it is the extreme warping of a black hole.  Boot gave a decent description above.  I just wanted to add another image that may help to visualize the concept.  This image, however is not for a black hole.  It models the shape of space around the earth.  It attempts to give you a sense of the "all direction" concept Boot was describing, but it still isn't fully accurate.  While you can see the curvature in additional directions, you still can't get ALL directions and end up creating awkward "corner" effects that are misleading.  Also, to extend this to be more representative as a black hole, imagine the "lines" all bending and converging to a single point instead of the surface of the earth.  

 
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Galileo said:
It is very difficult (impossible?) to produce an image that allows us to fully conceptualize the geometry of space around a mass, and even more difficult when it is the extreme warping of a black hole.  Boot gave a decent description above.  I just wanted to add another image that may help to visualize the concept.  This image, however is not for a black hole.  It models the shape of space around the earth.  It attempts to give you a sense of the "all direction" concept Boot was describing, but it still isn't fully accurate.  While you can see the curvature in additional directions, you can get ALL and end up creating awkward "corner" effects that are misleading.  Also, to extend this to be more representative as a black hole, imagine the "lines" all bending and converging to a single point instead of the surface of the earth.  
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Thanks. I was just trying to confirm that the photo I linked to was a simplified depiction. I like the pic you linked.

But...isn't an accretion disk flat? Wouldn't the disk be more like a funnel? No, that doesn't make sense. I don't know what shape it would be but why would it be flat. Wouldn't the spin that creates that also cause a funnel like entry into the black hole and not one from all directions? :headexplode:

 
Galileo said:
Amazing there is still power available for that craft to do anything...
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Its going to be picked up by aliens and giving many new features. Eventually, it will try to search for the creator. Sadly, it will view carbon based units in a bad light.

 
Basically, instead of this, it should be represented more like this.

eta: but the second one shows a singular direction.

 
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So, Im picturing a really strong magnet in the middle of a sphere made of pliable metal that is pulled towards the magnet yet keeps its shape sort of. Is that a sort of decent description of matter interacting with spacetime? I assume "spacetime" is like the sheet, while matter is like the ball in the middle of the sheet? 

 
jamny said:
Thanks. I was just trying to confirm that the photo I linked to was a simplified depiction. I like the pic you linked.

But...isn't an accretion disk flat? Wouldn't the disk be more like a funnel? No, that doesn't make sense. I don't know what shape it would be but why would it be flat. Wouldn't the spin that creates that also cause a funnel like entry into the black hole and not one from all directions? :headexplode:
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Normally an accretion disk is matter pulled from a companion star that orbits the black hole.  Or, they orbit each other but let's just say the star orbits the black hole for easy thinking.

So the gas flows off the star and towards the black hole.  Here would be a snapshot of one moment in time.

Now consider what happens when the star orbits around the black hole.  Matter keeps flowing towards the black hole all the way around. But it's staying in the plane formed by the star's orbit.  

The accretion disk is flat because there aren't other sources above and below contributing as significant amounts of matter.  But yes, there would still be matter there like your other image showed, just it is probably a trivial amount compared to what's coming from a companion star.

 
GregR said:
Normally an accretion disk is matter pulled from a companion star that orbits the black hole.  Or, they orbit each other but let's just say the star orbits the black hole for easy thinking.

So the gas flows off the star and towards the black hole.  Here would be a snapshot of one moment in time.

Now consider what happens when the star orbits around the black hole.  Matter keeps flowing towards the black hole all the way around. But it's staying in the plane formed by the star's orbit.  

The accretion disk is flat because there aren't other sources above and below contributing as significant amounts of matter.  But yes, there would still be matter there like your other image showed, just it is probably a trivial amount compared to what's coming from a companion star.
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Isn't an accretion disk flat because of the spin of the black hole? As the NOVA episode showed, there is not actual matter above and below the black hole in the first picture. It is the bending of light showing the disk behind the hole. It is the disk itself.

 
The accretion disk you guys are thinking of isn't really "in" the black hole.  The stuff we would see is still outside the event horizon...like water going down a drain isn't in the drain yet.  That shape you are envisioning is a product of angular momentum conservation and the natural tendency of stuff to tend towards a lower energy state.  Inside the black hole matter is crushed to infinite density...a singularity...no volume.  

 
Galileo said:
The accretion disk you guys are thinking of isn't really "in" the black hole.  The stuff we would see is still outside the event horizon...like water going down a drain isn't in the drain yet.  That shape you are envisioning is a product of angular momentum conservation and the natural tendency of stuff to tend towards a lower energy state.  Inside the black hole matter is crushed to infinite density...a singularity...no volume.  
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Right, but it is going in a particular direction, like a funnel. Not in all directions at the same time.

 
I should add...matter can absolutely fall into a black hole from all directions.  But there has to be matter there to fall in.  The accretion disk like the one shown in Greg's picture is from an abundance of matter coming towards the black hole from a particular direction (companion star) in the same rotational plane as the black hole.  Imagine you are on a play ground with a spinning merry go round.  If a whole bunch of kids ran up to the outer edge of that merry go round and grabbed on to an outer bar/handle, they would go flying around with the spinning merry go round in the same plane forming an accretion disk of kids!  But someone could still jump on the merry go round from a tree branch above.  There just aren't many kids coming from that direction.

 
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Galileo said:
The distortion of space would be from all directions towards the singularity  
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But wouldn't there be an added force (centrifugal?) due to the spin that would be stronger along the accretion disk plane than say, looking down at it from above? Obviously an outward force, so maybe weaker?

 
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Galileo said:
I should add...matter can absolutely fall into a black hole from all directions.  But there has to be matter there to fall in.  The accretion disk like the one shown in Greg's picture is from an abundance of matter coming towards the black hole from a particular direction (companion star).  Imagine you are on a play ground with a spinning merry go round.  If a whole bunch of kids ran up to the outer edge of that merry go round and grabbed on to an out bar/handle, they would go flying around with the spinning merry go round in the same plane forming an accretion disk of kids!  But someone could still jump on the merry go round from a tree branch above.  There just aren't many kids coming from that direction.
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Yes, similar example. :thumbup:

So, which is more accurate?

jamny said:
Basically, instead of this, it should be represented more like this.
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jamny said:
But wouldn't there be an added force (centrifugal?) due to the spin that would be stronger along the accretion disk plane than say, looking down at it from above?
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There would be a centripetal force...which is actually the gravitational force...which would be towards the center of the circular path where the singularity would be.  This does not mean that a gravitational force could not exist elsewhere.  There just would not be circular motion.  Someone at the North pole is still experiencing a force toward the center of the earth, but they are not traveling in a circle like a person would be at the equator.  The guy at the equator is pulled towards the center of the earth also, but because he has some tangential velocity as well he follows a circular path and we describe the inward force as centripetal (center seeking).  Both guys still experience gravity.

 
Galileo said:
 a sphere of debris in addition to any accretion disk. 
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That's exactly what I think it should be and questioned why it was portrayed as it is, with a directional flow towards an imaginary funnel. I guess it's an easier way to depict it but it's very misleading and confusing, imo.

 
jamny said:
That's exactly what I think it should be and questioned why it was portrayed as it is, with a directional flow towards an imaginary funnel. I guess it's an easier way to depict it but it's very misleading and confusing, imo.
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But if you show a sphere of debris, you can't see the "hole"!!!

 
The dimensions always get me. We can fit a million earth's inside the Sun. And they have found a black hole that is 30 billion times the mass of the Sun. What does that look like in an actual calculation? I think they said the black hole would encompass our entire galaxy.

 
jamny said:
The dimensions always get me. We can fit a million earth's inside the Sun. And they have found a black hole that is 30 billion times the mass of the Sun. What does that look like in an actual calculation? I think they said the black hole would encompass our entire galaxy.
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Mass of earth ~ 6 x 10^24 kg 

Mass of sun ~ 2 x 10^30 kg  (10^6 x more massive than earth)

30 billion x mass of sun would be (30 x 10^9) x (2 x 10^30) = 6 x 10^40 kg = 60,000,000,000,000,000,000,000,000,000,000,000,000,000 kg

ETA...the most recent published estimate for the mass of the Milky Way that I have seen is about 700 billion solar masses.

 
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I didn't realize James Webb launch was pushed back to Spring 2019. I thought it was late this year. :kicksrock:  

I also didn't realize it is expected to only be a 5 year mission, with hope of possibly 10. I'll be more nervous about that launch than any in a long time. It would be such a horrible loss if it fails.

 
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