The origin of the X-rays are not well understood, but are thought primarily to come from upscattering of thermal photons in a very hot atmosphere above the accretion disk. All the light basically comes from the stuff right around the black holes moving at relativistic speeds, not the black holes themselves.
The high supernova rate resulting from the burst of star formation is likely more of a problem than a central quasar, especially since the star formation can take place outside of the Galactic center. I give my intro astronomy students a problem to computer what the Galactic core would look like if it was a quasar and there was no intervening gas/dust (a really big if, since there is a lot of obscuration now).
Quasars can be 1000 times more luminous than an entire galaxy. The absolute magnitude of such a luminous quasar would be about M = -28.5. If the black hole in the center of our galaxy became a quasar, and obscuring gas and dust did not dim it, what would the apparent magnitude of the galactic core be? Think about the answer and what that would look like in the sky.
The answer is a magnitude of -13.9, about the same as the full moon. It would be more concentrated that the light of the moon, and you'd be able to see it in the day time. But, as I said, intervening gas/dust would diminish it's light, and the Milky Way and Andromeda do not have black holes massive enough to shine as brightly as my example. Our atmosphere would also be there to protect us from X-rays and UV, much as it does now.
I'll add that if you go to www.mikebrotherton.com, the cover art to my first novel Star Dragon shows an accretion disk around a white dwarf star. It isn't quite the same thing as a quasar, but it is similar and it's nice artwork (by Stephan Martinere, who deserves his name mentioned).
No, the black holes CAN'T splatter into pieces. They're too massive, their gravity too strong. All the "crap" around them -- gas, dust -- that is the fuel of the quasar -- that stuff surely does spew all over. The basic accretion process, when things settle down and merg, is for that material to form a flattened disk. When you see a quasar, it is the intense radiation from this hot disk that does all the shining. The black hole just provides the gravity. There may also be relativistic jets shooting out the spin axis, but their formation is not well understood. Neither are the less collimated outflows from around quasars (one of the reasons I'm suspicious about their results -- they're dealing with a broad brush and could be right on that level but we surely don't understand a lot of the details even on an empirical, observational level).
I've got some lecture slides on active galaxies (powerpoint) up at my astronomy website. Look at:
This link.
There are some some real images, and some artists renditions, you might like. I've just used the powerpoint web format, so it looks crappy in anything but explorer. Sorry.
Astronomy does pretty well with women, at least compared to other hard sciences. At the undergraduate level, it looks to be close to 50/50. Last year I think we had more female applicants for our summer REU program than males. We're going to admit more women than men into our graduate program this year, too. At the more senior levels, there are fewer women, but the numbers more or less match the historical demographics. My PhD advisor was female, and I have lots of female collaborators and a female grad student. Di Matteo isn't too old -- my generation, 30s. Physics, on the other hand, is still having its problems...
There are limits to quasar ages based on demographic arguments (the relic holes we see today compared to historical quasar activity and assumptions about the efficiency of the matter to energy conversion). The upper limit is on order of 100 million years or so. I know the timescale for "blowing out" gas/dust on Galactic scales from a powerful quasar is much shorter than that, more like 100,000 years, so I'm going to have to see the jounral article and see what they're saying in this paper. Big difference between those two numbers. Keep in mind that even 100 million years is relatively short compared to a unverse age of 13.7 billion years and may be the "short" timescale discussed.
This is my area of expertise, from the observational side. I've just finished writing a proposal (due today!) to observe "post-starburst quasars" in the infrared with the Spitzer Space Telescope. These are quasars that still show clear signs of massive starbursts, observations that can in principle test simulations like the ones discussed in the article. I've seen Di Matteo give a talk on this topic a year or two ago, and she strikes me as very good. I'm going to have to check out the new work closely -- I have suspicions that their explanation will fail in some details. But that's what makes science fun, finding the problems with ideas and fixing them, or forcing everyone to move on.
My whole field, astronomy, only has knowledge, data sets, and astronomical software as "products." I'm lucky, I guess, that way. We have politics in astronomy, but not so much and not so much bullshit. It also lets me play a pretty forceful science advocate. Understanding quasars doesn't require you to be liberal or conservative, just a good scientist. Science isn't the be all and end all of the world, but it is one of the most powerful tools mankind has at its disposable and potentially the most powerful force for good...if not abused.
I thought the parent post was funny moreso than trolling, especially given the other recent news of the day. There are parallels to be drawn between government attempting to subvert science and government attempting to subvert media. Both activities try to control public perception of facts by circumventing the people who have historically provided them.
Wow, what a partisan, science-hating post to make right out of the box! This doesn't address the issue of scientists expected to change their conclusions on the basis of politics, or the substance of the claims. Like scientists or not, but you can't in good faith ignore them just because you don't like their politics.
Science is the most powerful way of developing new and accurate information about the world we live in. By all means, make policy on the basis of more than science, but don't subvert science to advance wishful thinking. Everyone loses that way.
I double majored with electrical engineering and space physics, so I feel for you. The upper-level physics stuff IS just plain harder than many things you find elsewhere in school. If I wind up being forced to teach it (a possibility) I really need to work back up to it first, with some serious time set aside!
A more realistic factor is probably 4 or 5. If I can do an exam in 10-15 minutes, that's probably an ok hour exam. If it takes me longer than that, an hour is not enough time. I agree with you, that if it takes your prof an hour to do his own exam, that two hours is not enough for students.
Some of the energy is in the form of synchrotron, but this is more important in so-called radio-loud objects with jets, and is beamed along the jets. The vast majority of the radiation is thermal, either from the hot accretion disk or reprocessed radiotion from surround dust heated to a few hundred degrees kelvin. Quasars are my specialty.
That's kind of fun. Gregory Benford had a story reiniscent of that sort of thing, too, a few years ago. I've read Alistair Reynold's first novel Revelation Space but not the one you mention. I like his work pretty well, and he's the other new novelist with a PhD in astronomy like myself in the field, so I pay attention to him.
But the money it would take to repair Hubble is NOT going toward other telescopes, ground-based or not. It's just going...to where all the rest of that money goes, interest on the debt. Or foreign wars. One of those two for sure.
There were problems at NASA under Dan Goldin (e.g., the realization that onlt 2 out of 3 was possible with "better, faster, cheaper"), but I miss his vision. He gave talks at astronomy meetings (and other places, too) that were cutting edge, looking forward to great things. Inspiring. His strengths are all the more apparent in comparison to current NASA leadership.
O'Keefe is apparently on his way out, but I haven't heard any specific rumors about his replacement.
There are programs to do this. You can propose to Hubble for new observations, or you can propose to Hubble for money to analyze old observations. NASA has an entire pot of money set aside just to analyze archival space-based data (my post-doc and I just got about $200k to do some of this).
If you had a mobile system, you could keep a telescope in the dark constantly going a mere 10 mph or less (10 mph would be needed to circumnavigate the moon at its equator in a month). Also, there are craters near the poles that are in perpetual shadow. But, since there isn't an atmosphere to scatter light like there is on Earth, you could observe most of the sky in lunar daytime without very high backgrounds, so there isn't a need for being in the dark.
I really thought we could keep Hubble going until the James Webb Telescope goes up. Guess not. The proposal I just put in last month might be my last chance to do a new Hubble project (failure is expected for 2007, but could be sooner, or a little later). I've got some grant money to hire a postdoc, and one of my friends who currently works at Space Telescope is going to call me about it tomorrow. He says morale there is awful, and many are looking for outs. They'll be running James Webb, too, so there will be things to do, but still...
Using the moon as a shield from EM interference is a good reason. I have one target I've tried to observe at the VLA three times and interference messed it up each time. I eventually lost interest and gave up. Even though the FCC is supposed to protect many radio frequencies for astronomical use, the infringements have continued to creep in.
Both applied and basic research are valuable pursuits that have paid off in many ways. Basic research, like astronomy, often pays off much better in cultural value than economic, and that's okay by me. I'm not here on Earth just to make money to leave my family and government.
It certainly is! For a full-fledged professor, you're not doing so well.
I'm doing very well. Evolution, with a capital "E", that was the original point of this assinine creationist aside in an astronomy thread, as proposed initially by Dawrin, and the thing in the school textbooks mentioned above, is ONLY about speciation.
You've just proven my point, that you don't know what the "Theory of Evolution" is. There is no accepted scientific theory for the origin of life. There is a very well-accepted scientific theory for how life, once it existed, evolves. Call it a castle in the sky, or whatever you want, but please educate yourself on what you're talking about it.
And in general, take your religious pseudo-science and keep it out of astronomy threads in the future, please. You posted a lot in this thread, and essentially all off-topic. You're a waste of space here, and a waste of my time.
We always used to make these sort of estimates. In terms of actual cost Hubble is something like $10 a second, order of magnitude. Keck is $1 a second. Most research-capable telescopes charge at least a few hundred dollars a night, minimum, when actually selling time.
The economics doesn't really work, though. There would have to be grant money to pay for the telescope time, and someone (NASA, NSF) would have to hand it out. I'm funded at more than $100k a year, but a most of that goes directly to university overhead (40%), my summer salary, my postdoc's salary, travel, page charges (astronomers must pay to publish in the major US journals), etc. If I had to pay for telescope time, like Hubble, I'd have to put it in a budget and we'd likely be talking at most tens of thousands per year. Maybe the scheme could work out in the end, but you'd have to spend your billion dollars up front first, then hope everything works well and that there are enough astronomers with enough money to make it back over the useful lifetime of the telescope.
The current method, as awkward and uneconomic as it is, works better than most obvious, current alternatives. Perhaps cheap, private access to space would change this, but not in the immediate future.
Slashdot Mirror
The origin of the X-rays are not well understood, but are thought primarily to come from upscattering of thermal photons in a very hot atmosphere above the accretion disk. All the light basically comes from the stuff right around the black holes moving at relativistic speeds, not the black holes themselves.
The high supernova rate resulting from the burst of star formation is likely more of a problem than a central quasar, especially since the star formation can take place outside of the Galactic center. I give my intro astronomy students a problem to computer what the Galactic core would look like if it was a quasar and there was no intervening gas/dust (a really big if, since there is a lot of obscuration now).
Quasars can be 1000 times more luminous than an entire galaxy. The absolute magnitude of such a luminous quasar would be about M = -28.5. If the black hole in the center of our galaxy became a quasar, and obscuring gas and dust did not dim it, what would the apparent magnitude of the galactic core be? Think about the answer and what that would look like in the sky.
The answer is a magnitude of -13.9, about the same as the full moon. It would be more concentrated that the light of the moon, and you'd be able to see it in the day time. But, as I said, intervening gas/dust would diminish it's light, and the Milky Way and Andromeda do not have black holes massive enough to shine as brightly as my example. Our atmosphere would also be there to protect us from X-rays and UV, much as it does now.
I'll add that if you go to www.mikebrotherton.com, the cover art to my first novel Star Dragon shows an accretion disk around a white dwarf star. It isn't quite the same thing as a quasar, but it is similar and it's nice artwork (by Stephan Martinere, who deserves his name mentioned).
No, the black holes CAN'T splatter into pieces. They're too massive, their gravity too strong. All the "crap" around them -- gas, dust -- that is the fuel of the quasar -- that stuff surely does spew all over. The basic accretion process, when things settle down and merg, is for that material to form a flattened disk. When you see a quasar, it is the intense radiation from this hot disk that does all the shining. The black hole just provides the gravity. There may also be relativistic jets shooting out the spin axis, but their formation is not well understood. Neither are the less collimated outflows from around quasars (one of the reasons I'm suspicious about their results -- they're dealing with a broad brush and could be right on that level but we surely don't understand a lot of the details even on an empirical, observational level).
I've got some lecture slides on active galaxies (powerpoint) up at my astronomy website. Look at: This link. There are some some real images, and some artists renditions, you might like. I've just used the powerpoint web format, so it looks crappy in anything but explorer. Sorry.
Astronomy does pretty well with women, at least compared to other hard sciences. At the undergraduate level, it looks to be close to 50/50. Last year I think we had more female applicants for our summer REU program than males. We're going to admit more women than men into our graduate program this year, too. At the more senior levels, there are fewer women, but the numbers more or less match the historical demographics. My PhD advisor was female, and I have lots of female collaborators and a female grad student. Di Matteo isn't too old -- my generation, 30s. Physics, on the other hand, is still having its problems...
There are limits to quasar ages based on demographic arguments (the relic holes we see today compared to historical quasar activity and assumptions about the efficiency of the matter to energy conversion). The upper limit is on order of 100 million years or so. I know the timescale for "blowing out" gas/dust on Galactic scales from a powerful quasar is much shorter than that, more like 100,000 years, so I'm going to have to see the jounral article and see what they're saying in this paper. Big difference between those two numbers. Keep in mind that even 100 million years is relatively short compared to a unverse age of 13.7 billion years and may be the "short" timescale discussed.
This is my area of expertise, from the observational side. I've just finished writing a proposal (due today!) to observe "post-starburst quasars" in the infrared with the Spitzer Space Telescope. These are quasars that still show clear signs of massive starbursts, observations that can in principle test simulations like the ones discussed in the article. I've seen Di Matteo give a talk on this topic a year or two ago, and she strikes me as very good. I'm going to have to check out the new work closely -- I have suspicions that their explanation will fail in some details. But that's what makes science fun, finding the problems with ideas and fixing them, or forcing everyone to move on.
My whole field, astronomy, only has knowledge, data sets, and astronomical software as "products." I'm lucky, I guess, that way. We have politics in astronomy, but not so much and not so much bullshit. It also lets me play a pretty forceful science advocate. Understanding quasars doesn't require you to be liberal or conservative, just a good scientist. Science isn't the be all and end all of the world, but it is one of the most powerful tools mankind has at its disposable and potentially the most powerful force for good...if not abused.
I thought the parent post was funny moreso than trolling, especially given the other recent news of the day. There are parallels to be drawn between government attempting to subvert science and government attempting to subvert media. Both activities try to control public perception of facts by circumventing the people who have historically provided them.
Wow, what a partisan, science-hating post to make right out of the box! This doesn't address the issue of scientists expected to change their conclusions on the basis of politics, or the substance of the claims. Like scientists or not, but you can't in good faith ignore them just because you don't like their politics.
Science is the most powerful way of developing new and accurate information about the world we live in. By all means, make policy on the basis of more than science, but don't subvert science to advance wishful thinking. Everyone loses that way.
I double majored with electrical engineering and space physics, so I feel for you. The upper-level physics stuff IS just plain harder than many things you find elsewhere in school. If I wind up being forced to teach it (a possibility) I really need to work back up to it first, with some serious time set aside!
A more realistic factor is probably 4 or 5. If I can do an exam in 10-15 minutes, that's probably an ok hour exam. If it takes me longer than that, an hour is not enough time. I agree with you, that if it takes your prof an hour to do his own exam, that two hours is not enough for students.
Some of the energy is in the form of synchrotron, but this is more important in so-called radio-loud objects with jets, and is beamed along the jets. The vast majority of the radiation is thermal, either from the hot accretion disk or reprocessed radiotion from surround dust heated to a few hundred degrees kelvin. Quasars are my specialty.
That's kind of fun. Gregory Benford had a story reiniscent of that sort of thing, too, a few years ago. I've read Alistair Reynold's first novel Revelation Space but not the one you mention. I like his work pretty well, and he's the other new novelist with a PhD in astronomy like myself in the field, so I pay attention to him.
Absolutely! It is more of a fun idea than a serious suggestion.
But the money it would take to repair Hubble is NOT going toward other telescopes, ground-based or not. It's just going...to where all the rest of that money goes, interest on the debt. Or foreign wars. One of those two for sure.
There were problems at NASA under Dan Goldin (e.g., the realization that onlt 2 out of 3 was possible with "better, faster, cheaper"), but I miss his vision. He gave talks at astronomy meetings (and other places, too) that were cutting edge, looking forward to great things. Inspiring. His strengths are all the more apparent in comparison to current NASA leadership.
O'Keefe is apparently on his way out, but I haven't heard any specific rumors about his replacement.
There are programs to do this. You can propose to Hubble for new observations, or you can propose to Hubble for money to analyze old observations. NASA has an entire pot of money set aside just to analyze archival space-based data (my post-doc and I just got about $200k to do some of this).
If you had a mobile system, you could keep a telescope in the dark constantly going a mere 10 mph or less (10 mph would be needed to circumnavigate the moon at its equator in a month). Also, there are craters near the poles that are in perpetual shadow. But, since there isn't an atmosphere to scatter light like there is on Earth, you could observe most of the sky in lunar daytime without very high backgrounds, so there isn't a need for being in the dark.
I really thought we could keep Hubble going until the James Webb Telescope goes up. Guess not. The proposal I just put in last month might be my last chance to do a new Hubble project (failure is expected for 2007, but could be sooner, or a little later). I've got some grant money to hire a postdoc, and one of my friends who currently works at Space Telescope is going to call me about it tomorrow. He says morale there is awful, and many are looking for outs. They'll be running James Webb, too, so there will be things to do, but still...
Using the moon as a shield from EM interference is a good reason. I have one target I've tried to observe at the VLA three times and interference messed it up each time. I eventually lost interest and gave up. Even though the FCC is supposed to protect many radio frequencies for astronomical use, the infringements have continued to creep in.
Your high school physics didn't stick too well. The mass of the radio telescopes doesn't come into play in the way you think it does.
Both applied and basic research are valuable pursuits that have paid off in many ways. Basic research, like astronomy, often pays off much better in cultural value than economic, and that's okay by me. I'm not here on Earth just to make money to leave my family and government.
It certainly is! For a full-fledged professor, you're not doing so well.
I'm doing very well. Evolution, with a capital "E", that was the original point of this assinine creationist aside in an astronomy thread, as proposed initially by Dawrin, and the thing in the school textbooks mentioned above, is ONLY about speciation.
You've just proven my point, that you don't know what the "Theory of Evolution" is. There is no accepted scientific theory for the origin of life. There is a very well-accepted scientific theory for how life, once it existed, evolves. Call it a castle in the sky, or whatever you want, but please educate yourself on what you're talking about it.
And in general, take your religious pseudo-science and keep it out of astronomy threads in the future, please. You posted a lot in this thread, and essentially all off-topic. You're a waste of space here, and a waste of my time.
We always used to make these sort of estimates. In terms of actual cost Hubble is something like $10 a second, order of magnitude. Keck is $1 a second. Most research-capable telescopes charge at least a few hundred dollars a night, minimum, when actually selling time.
The economics doesn't really work, though. There would have to be grant money to pay for the telescope time, and someone (NASA, NSF) would have to hand it out. I'm funded at more than $100k a year, but a most of that goes directly to university overhead (40%), my summer salary, my postdoc's salary, travel, page charges (astronomers must pay to publish in the major US journals), etc. If I had to pay for telescope time, like Hubble, I'd have to put it in a budget and we'd likely be talking at most tens of thousands per year. Maybe the scheme could work out in the end, but you'd have to spend your billion dollars up front first, then hope everything works well and that there are enough astronomers with enough money to make it back over the useful lifetime of the telescope.
The current method, as awkward and uneconomic as it is, works better than most obvious, current alternatives. Perhaps cheap, private access to space would change this, but not in the immediate future.