Posted by
chrisd
on from the infinite-radius-finite-diameter dept.
paradox writes "Reuters is reporting that scientists have found a massive black hole 40,000 light-years away that could change the way scientists think about black holes. The mass of this particular black hole is 14 times the mass of the sun, compared to the typical mass of 3 to 7 suns."
Re:Size IS important.
by
zCyl
·
· Score: 5, Informative
But what about its physical size? I mean, when you are dealing with monstrous astro-physical phenoms beyond human comprehension, isn't it important to be boggled by the density?
Because there IS no size. A black hole by definition is a singularity, and has no conceivable dimensions. The closest thing a black hole has to a size is what's called the Schwarzschild radius, or the event horizon. This radius is the distance from the center at which light can no longer escape (ignoring Hawking radiation, another topic entirely). The Schwarzschild radius is equal to 2GM/c^2, where G is the gravitational constant, c is the speed of light, and M is the mass of the black hole. So the radius is really nothing more than a constant times the mass.
If you know the mass, and you don't have rotation, you know everything that can be known about it.
The event horizon of a 14 solar mass black hole would be about 84 kilometers in diameter. A planet could certainly orbit a black hole, and the orbit would be no different than that about a non-black hole of the same mass. (Though to be picky, neutron stars can't be as massive as 14 solar masses.)
Re:Size IS important.
by
cascino
·
· Score: 5, Informative
Technically the singularity itself possesses infinte density, and thus it's size cannot be resolved (i.e.: it's a single point, no matter how close you magnify it).
The Schwarzschild radius of such an object, however (better known as the "event horizon"), can be calculated fairly simply using a variation of the escape velocity formula
Rs = 2*G*M / c^2
Where G is the gravitational constant, M is the mass of the object, and c is the speed of light.
Plugging the numbers into the equation yields a radius of 2.95 * 10^6 km. Therefore this black hole has a radius just over four times the size of the sun, and an area 16 times as large. Compared to black holes usually on scales relative to that of the Earth, that's REAL big.
non-watered down story
by
ChazeFroy
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· Score: 5, Informative
Here's a link to the European Southern Observatory story that's not watered down (gotta love Reuters and AP like that!).
Re:Size IS important.
by
the_2nd_coming
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· Score: 5, Informative
no a sigularity is the center of a black hole, it is where space time becomes undefind. a black hole is the defined by the eventhorizon. so it does have a size. if it is just a sigularity it is not a black hole, it is a naked sigularity.
--
I am the Alpha and the Omega-3
Stellar, middle-weight, supermassive
by
michaeldouma
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· Score: 5, Informative
There are three main classes of black hole. This article relates to the "stellar" type...
Astronomers suspect that most black holes are produced when massive stars (at least 8-10 times the Sun's mass) reach the end of their lifecycle. This is a so-called "stellar black hole." Stellar black holes are the remains of dead stars several times heavier than the Sun, compressed to a diameter of a few miles or less. Supermassive black holes have masses comparable to those of a typical galaxy. These masses range anywhere from a million to 100 billion of our Suns. Supermassive black holes tend to be in the centers of galaxies, creating what are called Active Galactic Nuclei (AGNs). They may have formed in the early universe from giant gas clouds or from the collapse of clusters of immense numbers of stars. Lastly, the field of black holes, formerly dominated by heavyweights packing the gravitational punch of a billion Suns and lightweights just a few times heavier than our Sun, has another contender, the middleweight black holes, weighing in at 100 to 10,000 Suns.
Re:Size IS important.
by
Anonymous Coward
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· Score: 1, Informative
When an object collapses to a black hole, all the matter crunches down to a singularity of zero size. But the singularity is not the black hole. The black hole is a region of space outside (and including) the singularity, from which light cannot escape. That region has a finite size.
P.S. If the Earth turned into a black hole, it would be about a centimeter across.
Re:Size IS important.
by
Anonymous Coward
·
· Score: 1, Informative
In other words, the matter that was formally the Earth woould not take up any space at all (it would crush down to zero size) but its horizon (the area of space that it caused all light/matter/etc to be pulled in) would be about the diameter of a basketball. Or a marble. Depending on whom you ask.
A nice little presentation on black holes can be found here.
http://archive.ncsa.uiuc.edu/Cyberia/NumRel/Blac kH oleFormation.html if you are paranoid.
14x is a big deal. The 100-100000 solar mass black holes at the center of galaxies (which still isn't proven, but has a lot of data pointing towards it) are not stellar black holes. They would be called galactic black holes. Stellar black holes are byproducts of dead stars. The Chandra limit, 1.4 solar masses, is the minimum mass that is needed to make stellar remnants collapse. If it is over 2 or 3 solar masses, then it collapses all the way into a black hole. Now, that was figured out several decades ago, so of course that number might be slightly "off," but I seriously doubt that Chandra was off by a factor of 10. I'm curious where you get 10-100 solar masses from...
When a star with a mass of ~30 solar masses or higher dies, it supernovas, blowing off most of its mass. IF WHAT'S LEFT is greater than a couple of solar masses (and within the Schwarzschild radius), then it collapses into a black hole. I repeat: it MUST ONLY be more massive than a few (2 or 3 - it's under debate) solar masses! True, the original star must be greater than ~30 solar masses; but the mass of the black hole is far less than the mass of the original star. THIS is why a 14 solar mass black hole is so strange!
By the way, NO information regarding black holes is the subject of "worldwide consensus".
-- The best way to predict the future is to invent it.
Re:Size IS important.
by
Anonymous Coward
·
· Score: 2, Informative
Actually, speaking as someone studying in the field of quantum gravity, the question of whether singularities exist is still very much up in the air, though many people hope that Planckian physics will remove them. There are even some tentative results in that direction. On the other hand, it has been suggested that quantum gravity must contain at least "mild" singularities. So it is rather premature to claim that "most scientists" (or even most quantum gravity theorists) have abandoned the idea of a singularity.
I just ran across this that would certainly explain a couple things:
The Question We are deeply indebted to you if you can help us in obtaining two representative images about: 1)the real image (picture) of a "black hole" (photographed) 2)the most distant part of the Universe ever photographed.
The Answer 1) There are no "real" pictures of a black hole. This is because black holes themselves do not emit of reflect any light (that's why they are called black holes), and they are too small and too far away to be imaged. There are images of binary star systems consisting of one normal star and one black hole, and of the central regions of Galaxies that are believed to contain black holes. There are some examples of the latter, taken with the Hubble Space Telescope, at: http://imagine.gsfc.nasa.gov/docs/ask_astro/answer s/970318d.html
But these pictures don't actually show a black hole, you need to study the motion of stars to infer that there must be a black hole.
These are some of the most distant galaxies ever photographed; although some quasars are believed to be more distant, they make boring photographs (they just look like a point of light).
Best wishes,
Koji Mukai
(no, this isn't my work, I just found it on a Google Search)
-- I'm not a prophet or a stone-age man,
I'm just a mortal with potential of a super man.
article on the science journal nature,
by
vikool
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· Score: 5, Informative
here is the article on the science journal nature, it is slightly more detailed than the one on reuters
Re:Size IS important.
by
sigwinch
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· Score: 5, Informative
A black hole is a singularity.
It's important to remember that a singularity is a mathematical artifact where a physical property has no meaningful definition when measured by a particular metric. For instance, the north pole of the Earth is a longitude singularity, a point where the very concept of longitude ceases to have physical meaning.
It has no size, and therefore its density is infinite.
Actually, that turns out not to be the case, at least not relative to our reference frame. Imagine you're a distant (and indestructible!) observer watching a star collapse into a black hole. The more it collapses, the more it is affected by gravitational time dilation: time appears to run slower for the matter in the star than for the observer. Clocks in the star slow down. Light travelling away from the star is shifted towards the red end of the spectrum.
The more the star shrinks, the more it is affected by gravitational time dilation, and thus the more slowly it collapses as measured by the outside observer. The collapse thus asymptotically approaches infinite time dilation, and appears to freeze in time to the distant observer. Its physical size at the asymptote is the size of the event horizon, a.k.a. the Schwarzchild radius.
One way of measuring the star is to ask how long it would take light to travel from its outside edge to its center, as measured by a distant observer. (Theoretically, of course, as the star would absorb any light.) Think of it as the radius measured in units of literal light years. As the collapse approaches infinite time dilation, the 'light radius' approaches infinity. This is the singularity at the center of the black hole, and is a mathematical construct arising from the distant observer's point of view. It does not mean that density or any local physical parameter is infinite
I'm deliberately ignoring what the collapse looks like to an observer inside the star. Known physics simply cannot make any meaningful predictions, except that it will never be observable from the outside (because it literally takes an eternity to occur).
--
-- Kuro5hin.org: where the good times never end.;-)
Re:Size IS important.
by
Anonymous Coward
·
· Score: 1, Informative
It's important to remember that a singularity is a mathematical artifact where a physical property has no meaningful definition when measured by a particular metric . For instance, the north pole of the Earth is a longitude singularity, a point where the very concept of longitude ceases to have physical meaning.
You are confusing coordinate singularities (such as the longitude singularity you describe, or the event horizon singularity in Schwarzschild coordinates) with a true curvature singularity (such as at the center of a black hole). The former is a mathematical artifact of your choice of coordinate system in describing the metric; the latter is physical.
It has no size, and therefore its density is infinite.
Actually, that turns out not to be the case, at least not relative to our reference frame.
An external observer can't assign a size, zero or nonzero, to something within the horizon. It's true that an external observer will measure the size of the collapsing object to asymptotically approach the Schwarzschild radius, but that has nothing to do with the size of the singularity itself.
This is the singularity at the center of the black hole, and is a mathematical construct arising from the distant observer's point of view. It does not mean that density or any local physical parameter is infinite
Not true. The presence of the singularity is local and has nothing to do with any external observer's perception. For instance, if you compute the curvature scalar (contraction of the Ricci tensor), which is a local physical observable, it will blow up at the singularity.
Re:Where the hell did those figures come from?
by
Rasta+Prefect
·
· Score: 2, Informative
Actuallly no, the majority of black holes are stellar black holes. These are created by the collapse of giant stars and are generally a few suns in mass. 1.4 being about the lower end for collapse, I believe. Take an astronomy course.
-- Why?
initial report
by
vikool
·
· Score: 2, Informative
this page gives the first report of an anomaly that came about on the GRS1915+105
Slashdot Mirror
But what about its physical size? I mean, when you are dealing with monstrous astro-physical phenoms beyond human comprehension, isn't it important to be boggled by the density?
Because there IS no size. A black hole by definition is a singularity, and has no conceivable dimensions. The closest thing a black hole has to a size is what's called the Schwarzschild radius, or the event horizon. This radius is the distance from the center at which light can no longer escape (ignoring Hawking radiation, another topic entirely). The Schwarzschild radius is equal to 2GM/c^2, where G is the gravitational constant, c is the speed of light, and M is the mass of the black hole. So the radius is really nothing more than a constant times the mass.
If you know the mass, and you don't have rotation, you know everything that can be known about it.
The event horizon of a 14 solar mass black hole would be about 84 kilometers in diameter. A planet could certainly orbit a black hole, and the orbit would be no different than that about a non-black hole of the same mass. (Though to be picky, neutron stars can't be as massive as 14 solar masses.)
Technically the singularity itself possesses infinte density, and thus it's size cannot be resolved (i.e.: it's a single point, no matter how close you magnify it).
The Schwarzschild radius of such an object, however (better known as the "event horizon"), can be calculated fairly simply using a variation of the escape velocity formula
Rs = 2*G*M / c^2
Where G is the gravitational constant, M is the mass of the object, and c is the speed of light.
Plugging the numbers into the equation yields a radius of 2.95 * 10^6 km. Therefore this black hole has a radius just over four times the size of the sun, and an area 16 times as large. Compared to black holes usually on scales relative to that of the Earth, that's REAL big.
Here's a link to the European Southern Observatory story that's not watered down (gotta love Reuters and AP like that!).
no a sigularity is the center of a black hole, it is where space time becomes undefind. a black hole is the defined by the eventhorizon. so it does have a size. if it is just a sigularity it is not a black hole, it is a naked sigularity.
I am the Alpha and the Omega-3
Astronomers suspect that most black holes are produced when massive stars (at least 8-10 times the Sun's mass) reach the end of their lifecycle. This is a so-called "stellar black hole." Stellar black holes are the remains of dead stars several times heavier than the Sun, compressed to a diameter of a few miles or less. Supermassive black holes have masses comparable to those of a typical galaxy. These masses range anywhere from a million to 100 billion of our Suns. Supermassive black holes tend to be in the centers of galaxies, creating what are called Active Galactic Nuclei (AGNs). They may have formed in the early universe from giant gas clouds or from the collapse of clusters of immense numbers of stars. Lastly, the field of black holes, formerly dominated by heavyweights packing the gravitational punch of a billion Suns and lightweights just a few times heavier than our Sun, has another contender, the middleweight black holes, weighing in at 100 to 10,000 Suns.
P.S. If the Earth turned into a black hole, it would be about a centimeter across.
In other words, the matter that was formally the Earth woould not take up any space at all (it would crush down to zero size) but its horizon (the area of space that it caused all light/matter/etc to be pulled in) would be about the diameter of a basketball. Or a marble. Depending on whom you ask.
c kH oleFormation.html if you are paranoid.
A nice little presentation on black holes can be found here.
http://archive.ncsa.uiuc.edu/Cyberia/NumRel/Bla
14x is a big deal. The 100-100000 solar mass black holes at the center of galaxies (which still isn't proven, but has a lot of data pointing towards it) are not stellar black holes. They would be called galactic black holes. Stellar black holes are byproducts of dead stars. The Chandra limit, 1.4 solar masses, is the minimum mass that is needed to make stellar remnants collapse. If it is over 2 or 3 solar masses, then it collapses all the way into a black hole. Now, that was figured out several decades ago, so of course that number might be slightly "off," but I seriously doubt that Chandra was off by a factor of 10. I'm curious where you get 10-100 solar masses from...
When a star with a mass of ~30 solar masses or higher dies, it supernovas, blowing off most of its mass. IF WHAT'S LEFT is greater than a couple of solar masses (and within the Schwarzschild radius), then it collapses into a black hole. I repeat: it MUST ONLY be more massive than a few (2 or 3 - it's under debate) solar masses! True, the original star must be greater than ~30 solar masses; but the mass of the black hole is far less than the mass of the original star. THIS is why a 14 solar mass black hole is so strange!
By the way, NO information regarding black holes is the subject of "worldwide consensus".
The best way to predict the future is to invent it.
Actually, speaking as someone studying in the field of quantum gravity, the question of whether singularities exist is still very much up in the air, though many people hope that Planckian physics will remove them. There are even some tentative results in that direction. On the other hand, it has been suggested that quantum gravity must contain at least "mild" singularities. So it is rather premature to claim that "most scientists" (or even most quantum gravity theorists) have abandoned the idea of a singularity.
I just ran across this that would certainly explain a couple things:
r s/970318d.html
r s/970318d.html
The Question We are deeply indebted to you if you can help us in obtaining two representative images about: 1)the real image (picture) of a "black hole" (photographed) 2)the most distant part of the Universe ever photographed.
The Answer 1) There are no "real" pictures of a black hole. This is because black holes themselves do not emit of reflect any light (that's why they are called black holes), and they are too small and too far away to be imaged. There are images of binary star systems consisting of one normal star and one black hole, and of the central regions of Galaxies that are believed to contain black holes. There are some examples of the latter, taken with the Hubble Space Telescope, at: http://imagine.gsfc.nasa.gov/docs/ask_astro/answe
But these pictures don't actually show a black hole, you need to study the motion of stars to infer that there must be a black hole.
2) Again, you may want to look at some Hubble pictures (with explanations): http://imagine.gsfc.nasa.gov/docs/ask_astro/answe
These are some of the most distant galaxies ever photographed; although some quasars are believed to be more distant, they make boring photographs (they just look like a point of light).
Best wishes,
Koji Mukai
(no, this isn't my work, I just found it on a Google Search)
I'm not a prophet or a stone-age man,
I'm just a mortal with potential of a super man.
http://www.nature.com/nsu/011129/011129-13.html
vikas
The more the star shrinks, the more it is affected by gravitational time dilation, and thus the more slowly it collapses as measured by the outside observer. The collapse thus asymptotically approaches infinite time dilation, and appears to freeze in time to the distant observer. Its physical size at the asymptote is the size of the event horizon, a.k.a. the Schwarzchild radius.
One way of measuring the star is to ask how long it would take light to travel from its outside edge to its center, as measured by a distant observer. (Theoretically, of course, as the star would absorb any light.) Think of it as the radius measured in units of literal light years. As the collapse approaches infinite time dilation, the 'light radius' approaches infinity. This is the singularity at the center of the black hole, and is a mathematical construct arising from the distant observer's point of view. It does not mean that density or any local physical parameter is infinite
I'm deliberately ignoring what the collapse looks like to an observer inside the star. Known physics simply cannot make any meaningful predictions, except that it will never be observable from the outside (because it literally takes an eternity to occur).
-- ;-)
Kuro5hin.org: where the good times never end.
You are confusing coordinate singularities (such as the longitude singularity you describe, or the event horizon singularity in Schwarzschild coordinates) with a true curvature singularity (such as at the center of a black hole). The former is a mathematical artifact of your choice of coordinate system in describing the metric; the latter is physical.
An external observer can't assign a size, zero or nonzero, to something within the horizon. It's true that an external observer will measure the size of the collapsing object to asymptotically approach the Schwarzschild radius, but that has nothing to do with the size of the singularity itself.
Not true. The presence of the singularity is local and has nothing to do with any external observer's perception. For instance, if you compute the curvature scalar (contraction of the Ricci tensor), which is a local physical observable, it will blow up at the singularity.
Actuallly no, the majority of black holes are stellar black holes. These are created by the collapse of giant stars and are generally a few suns in mass. 1.4 being about the lower end for collapse, I believe. Take an astronomy course.
Why?
http://www.nature.com/doifinder/10.1038/35107019
vikas