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Russ
2004-Feb-18, 07:52 PM
I found this item http://channels.attbusiness.net/index.cfm?fuseAction=viewNewsArticle&nav_id=33&cat egory_name=Science&article_id=2c5d9202fb2d22075b81 3e6150e28e9b
about a black hole that is ripping a star apart. One would think that they would include Pics from Chandra but they don't. Has anyone seen this elsewhere, where they had a picture?

I'd really like to see what the astronomers are looking at, to see a jpg movie or some kind of data. Anybody got anything? :o

Kebsis
2004-Feb-18, 08:29 PM
I feel bad for anyone living on a planet that orbited that star.

Russ
2004-Feb-18, 09:11 PM
I feel bad for anyone living on a planet that orbited that star.
This is just a SWAG mind you, but I think that given the radiation level of a galatic center, if there was a planet capable of orbiting that star, nothing would be living on it. :wink:

sarongsong
2004-Feb-18, 09:35 PM
anyone seen this elsewhere, where they had a picture?---Russ
Artist rendition:
http://apnews.myway.com/article/20040218/D80PREA80.html
http://ak.imgfarm.com/images/ap/thumbnails//DOOMED_STAR.sff_LA500_20040218001906.jpg

George
2004-Feb-18, 10:54 PM
Reuter's version...>>> here (http://www.reuters.co.uk/newsPackageArticle.jhtml?type=topNews&storyID=4609 32&section=news) <<<

BBC ver....>>> here (http://news.bbc.co.uk/2/hi/science/nature/3501313.stm) <<<

USA Today...>>> here (http://www.usatoday.com/tech/news/2004-02-18-blackhole-sun_x.htm) <<<

http://images.usatoday.com/tech/_photos/2004/02-18-blackhole-main.jpg

George
2004-Feb-18, 11:02 PM
This is likely too simple a question but I am curious....

Is the high energy radiation the result of gas compression prior to crossing the EH [edit] or is there a thermo equation I'm forgetting regarding acceleration and heat?

George
2004-Feb-18, 11:06 PM
This is likely too simple a question but I am curious....

Is the high energy radiation the result of gas compression prior to crossing the EH or is there a thermo equation I'm forgetting regarding acceleration and heat?

[sorry, obviously I hit "quote" instead of "edit"]

AGN Fuel
2004-Feb-18, 11:12 PM
This is likely too simple a question but I am curious....

Is the high energy radiation the result of gas compression prior to crossing the EV or is there a thermo equation I'm forgetting regarding acceleration and heat?

The X-Ray emissions are typically the result of friction in the accretion disc material feeding the BH.

George
2004-Feb-18, 11:49 PM
This is likely too simple a question but I am curious....

Is the high energy radiation the result of gas compression prior to crossing the EV or is there a thermo equation I'm forgetting regarding acceleration and heat?

The X-Ray emissions are typically the result of friction in the accretion disc material feeding the BH.

Thanks. Very logical. The first artist rendition implied a somewhat direct feed into the BH. I should have known this was erroneous (bad astronomy :) ). :)

AGN Fuel
2004-Feb-19, 01:26 AM
This is likely too simple a question but I am curious....

Is the high energy radiation the result of gas compression prior to crossing the EV or is there a thermo equation I'm forgetting regarding acceleration and heat?

The X-Ray emissions are typically the result of friction in the accretion disc material feeding the BH.

Thanks. Very logical. The first artist rendition implied a somewhat direct feed into the BH. I should have known this was erroneous (bad astronomy :) ). :)

Interestingly, if the SMBH gets too massive, it can reach a point called the Hills Limit. This is where the Event Horizon extends to a radius further than that where the gravitational tidal forces 'shred' the star. Effectively, the star is destroyed inside the EV and no indication of it's destruction is received by a distant observer.

As a result, it is possible that SMBH's may become quiescent with evolution, even though they are still 'feeding'.

Edymnion
2004-Feb-19, 04:17 AM
Interestingly, if the SMBH gets too massive, it can reach a point called the Hills Limit. This is where the Event Horizon extends to a radius further than that where the gravitational tidal forces 'shred' the star. Effectively, the star is destroyed inside the EV and no indication of it's destruction is received by a distant observer.Okay, you're going to have to explain this one to me, as it doesn't jive with what I've been taught about black holes.

To my knowledge, the Event Horizen is the point in space where the gravity becomes so intense that nothing can escape it, not even light. There is still gravity from the black hole outside of the Event Horizen. The larger the hole, the larger the radius of the event horizen, but also the farther out that the normal gravity reaches as well.

How can the EH ever come close to equalling the radius of it's conventional gravitation field?

harlequin
2004-Feb-19, 05:43 AM
Interestingly, if the SMBH gets too massive, it can reach a point called the Hills Limit. This is where the Event Horizon extends to a radius further than that where the gravitational tidal forces 'shred' the star. Effectively, the star is destroyed inside the EV and no indication of it's destruction is received by a distant observer.Okay, you're going to have to explain this one to me, as it doesn't jive with what I've been taught about black holes.

To my knowledge, the Event Horizen is the point in space where the gravity becomes so intense that nothing can escape it, not even light. There is still gravity from the black hole outside of the Event Horizen. The larger the hole, the larger the radius of the event horizen, but also the farther out that the normal gravity reaches as well.

How can the EH ever come close to equalling the radius of it's conventional gravitation field?

It does not and AGN fuel did not say it. Indeed what in the world do you even mean by "radius of it's conventional gravitation field"? We are in the gravitational field of every object in the universe which we can observe.

Basically what is being said is that the Roche limit is inside the event horizon. So gravity will rip the star apart after it is inside the Event Horizon and not after. Tidal forces are caused by part of a body closest to the black hole (or whatever) experiencing a greater gravity than the part of it that is farthest away. If the difference in graviational forces the two sides of a body is great enough the body is ripped appart. Notice it is that difference and not the absolute strength of the gravity that does the ripping appart. It is the strength of the gravity that determines whether or not anything can get out. If the black hole is big enough that one can get to the event horizon without being ripped up.

AGN Fuel
2004-Feb-19, 06:14 AM
Interestingly, if the SMBH gets too massive, it can reach a point called the Hills Limit. This is where the Event Horizon extends to a radius further than that where the gravitational tidal forces 'shred' the star. Effectively, the star is destroyed inside the EV and no indication of it's destruction is received by a distant observer.Okay, you're going to have to explain this one to me, as it doesn't jive with what I've been taught about black holes.

To my knowledge, the Event Horizen is the point in space where the gravity becomes so intense that nothing can escape it, not even light. There is still gravity from the black hole outside of the Event Horizen. The larger the hole, the larger the radius of the event horizen, but also the farther out that the normal gravity reaches as well.

How can the EH ever come close to equalling the radius of it's conventional gravitation field?

It does not and AGN fuel did not say it. Indeed what in the world do you even mean by "radius of it's conventional gravitation field"? We are in the gravitational field of every object in the universe which we can observe.

Basically what is being said is that the Roche limit is inside the event horizon. So gravity will rip the star apart after it is inside the Event Horizon and not after. Tidal forces are caused by part of a body closest to the black hole (or whatever) experiencing a greater gravity than the part of it that is farthest away. If the difference in graviational forces the two sides of a body is great enough the body is ripped appart. Notice it is that difference and not the absolute strength of the gravity that does the ripping appart. It is the strength of the gravity that determines whether or not anything can get out. If the black hole is big enough that one can get to the event horizon without being ripped up.

Exactly.

The Event Horizon (more properly the 'Schwarzchild Radius') is not a point in space, but a region of space. How big that region is depends on how massive the singularity in the middle of it is!

A useful way to think about it is that you have a huge amount of mass at a point, which mass (of course) has a gravitational attraction. As you move further & further away, the calculated escape velocity from that mass reduces - at the point where the escape velocity is equivalent to the speed of light represents the Schwartzchild Radius.

Now, for a Supermassive Black Hole, the Schwartzchild Radius can be really big - Solar System sized or more. But as Harlequin pointed out, the disruption (isn't that a great euphemism?) to the star occurs due to the differential in gravitational attraction to the SMBH across the diameter of the star. So even though the gravitational attraction as a whole may still be immense, at a distance of (say) 40AU, the differential of the gravitational attraction from one side to the other is not so large as to tear the star apart. The the star can find itself inside the Event Horizon, but not 'disrupted'.

To an outside observer therefore, the star goes in whole and is never heard from again, because the shredding doesn't occur until after it is inside the EH.

This doesn't happen with stellar remnant BH's, because the Schwartzchild Radius is so much closer to the BH itself, that the tidal effects come into play before anything reaches the EH.

AKONI
2004-Feb-19, 12:10 PM
This story reminded me of something that happened to me when I was a kid. I had just seen the Disney movie The Black Hole a few days before my class went to the planetarium at a local high school. At the end the teacher in charge at the high school took questions. I asked him something about black holes and he rolled his eyes at me and told me they didn't exist. Well, right after that the next few questions were about black holes (I guess no one believed him), and he got angry with me for bringing it up in the first place.

I think it's funny that I got more accurate astronomy from a Disney movie that day than I did a high school science teacher


Anyway, I do have a question... Is there a chance the material being flung into space will coalesce into something or will it definitely continue to disperse?

George
2004-Feb-19, 02:15 PM
The Event Horizon (more properly the 'Schwarzchild Radius') is not a point in space, but a region of space. How big that region is depends on how massive the singularity in the middle of it is!

A useful way to think about it is that you have a huge amount of mass at a point, which mass (of course) has a gravitational attraction. As you move further & further away, the calculated escape velocity from that mass reduces - at the point where the escape velocity is equivalent to the speed of light represents the Schwartzchild Radius.

Now, for a Supermassive Black Hole, the Schwartzchild Radius can be really big - Solar System sized or more. But as Harlequin pointed out, the disruption (isn't that a great euphemism?) to the star occurs due to the differential in gravitational attraction to the SMBH across the diameter of the star. So even though the gravitational attraction as a whole may still be immense, at a distance of (say) 40AU, the differential of the gravitational attraction from one side to the other is not so large as to tear the star apart. The the star can find itself inside the Event Horizon, but not 'disrupted'.

To an outside observer therefore, the star goes in whole and is never heard from again, because the shredding doesn't occur until after it is inside the EH.

This doesn't happen with stellar remnant BH's, because the Schwartzchild Radius is so much closer to the BH itself, that the tidal effects come into play before anything reaches the EH.

Interesting but not inuitive. If the gravity just inside the Schwartzchild Radius is so intense as to not allow even light to escape, I would have guessed the tidal stresses outside the SR would be adequate to shred it's meal.

In a whole "gobble" action from a SMBH, is there no gravitational "ripple" or something caused by the "gulpee" whose highly accelerating mass is now disturbing the gravitational field? (I keep thinking about that "Bb" wave found in a galaxy that was mentioned a few months ago supposedly caused by some sort of SMBH.)

JohnOwens
2004-Feb-19, 05:55 PM
Interesting but not inuitive. If the gravity just inside the Schwartzchild Radius is so intense as to not allow even light to escape, I would have guessed the tidal stresses outside the SR would be adequate to shred it's meal.

Thing is, the force of gravity is an inverse square relation to the distance, while the tidal force (which does the shredding) is an inverse cube relation. (Schwarzschild radius is a direct relation.) So, when you get to where the SR is distant enough, even though the gravity is still terribly strong, the difference between how hard the near side is being sucked in, and how hard the far side is being sucked in, isn't great enough to shred it.
Just to give an abstract example, if you have a BH that has a mass 10 times greater than another, it will have a SR 10 times greater, and the gravitational pull at the SR will be 10 times less (10 times more mass, but radius is squared, so 100 times weaker), and the tidal forces at the SR will be 100 times less (10 times mass, divide by radius cubed now, 1000). That's why a SMBH (I assume we're using that as abbreviation for "super massive..."?) is relatively safe to approach.

George
2004-Feb-19, 06:06 PM
Thing is, the force of gravity is an inverse square relation to the distance, while the tidal force (which does the shredding) is an inverse cube relation. (Schwarzschild radius is a direct relation.) So, when you get to where the SR is distant enough, even though the gravity is still terribly strong, the difference between how hard the near side is being sucked in, and how hard the far side is being sucked in, isn't great enough to shred it.
Just to give an abstract example, if you have a BH that has a mass 10 times greater than another, it will have a SR 10 times greater, and the gravitational pull at the SR will be 10 times less (10 times more mass, but radius is squared, so 100 times weaker), and the tidal forces at the SR will be 100 times less (10 times mass, divide by radius cubed now, 1000). That's why a SMBH (I assume we're using that as abbreviation for "super massive..."?) is relatively safe to approach.

Thanks. I think I see now. If a star is approaching the SR of a SMBH, then the tidal stress is minimized due to the distance away from the center (the inverse cube of a much larger distance). The gravity gradient, although enormous, is more gentle due to its vastness.