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Black Hole Search Begins In Australian Outback
Sandeater writes: "BBC news is reporting that an new telescope has just been completed to search out black holes from the Australian outback. The astronomers using the telescope will be looking for huge black holes at the centres of galaxies, as well as seeing how they evolve.
The Cangaroo II will be offically opened tomorrow.
The BBC link can be found here."
Once you get past the event horizon, it *does* look suspiciously like Australia. I got there through L-space once, purely by accident. There I was, in the back of a Barnes & Noble, browsing the Terry Pratchett section, and before I knew it, BLAM! There I was in a rather demented futuristic Australian Outback. I know it was a black hole because they worshipped people from the movie. Needless to say, I found the nearest local bookseller, and got back home before dinner got cold.
It's probably the space time flux caused by that wandering entity who likes to add on bits to worlds that look like Australia retroactively that causes the black holes in the first place. Just another case of Science imitating Science Fiction...
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IMHO, Australia is a brilliant place for such observations. The sky is crystal-clear (relative to anywhere in the northern hemisphere) and there is a lot of empty space to build a telescope without burger bars, shopping malls and strip joints surrounding it within a week.
I've often wondered if Australia might be a good place for SETI, for the same reason. Sod the 1Km array! It would be practical to build a 5 mile array Down Under. (A 5 mile array would give you an image 18 pixels x 18 pixels of an Earth-sized planet, 1 Astronomical Unit from a Sol-like star, up to 100 light-years away. That would be enough resolution to check the atmosphere, determine the climate and look for radio leakage rather than deliberate signals.)
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
Good reply, you obviously know what you're talking about. However the main reason you use a ground based telescope is that you require a detector the size of a football pitch to see enough gamma rays of this energy to say anything useful. Thus it's impractical to launch one into space. Instead you use the atmosphere as your detector. Space based telescopes exist already which see lower energy gamma radiation from blazars, such as CGRO . I should also mention the experiment which discovered very high energy gamma rays from blazars, using the Cerenkov technique: The Whipple experiment (a blatant plug for my own PhD experiment!).
The purpose of orbiting telescopes is to avoid atmospheric absorption/distortion of the signal. Earth's atmosphere is opaque to many bands of IR and UV lights corresponding to atomic and molecular transition lines. Of course, atmospheric turbulence can wreak havoc with visible light. However, at the high X-ray energies they are looking at, the atmosphere is practiaclly transparent.
Also, the cost of an orbiting satellite is significantly higher than that of a ground based instrument, and with the booming Australian and Japanese space programs, they would have had to shell out more bucks to NASA or ESA to launch the thing.
Eric
The interesting thing I found about this is that unlike the reasoning behind Hubble (the atmosphere distorts light so get outside it) the Cangaroo II telescopes will use that very distortion to view the black holes.
I'd assume that the Southern Skies are a lot less mapped than their Northern cousins given the dearth of countries south of the equator.
But if they'd really wanted to go to a place where the atmosphere distorts the view then a Cafe Bar in Amsterdam would be their best bet
An Eye for an Eye will make the whole world blind - Gandhi
Umm so modern Astro-physics is all bollocks then.
Astro physics is one area where they just love to throw away theories and start with new ones. Black Holes have been postulated and the postulations found to be correct. The problem is viewing something that by definition doesn't emit light because its as dense as a Christian Coalition convention.
A lot of Astro-physicists would just love to be the one who writes the seminal paper
"The big bang is bollocks, the Universe is created from paper clips and buttons that disappear down the backs of sofas"
The aim of scientists is to be respected, and respect is earnt by proving others right beyond any doubt or best of all proving as many people wrong as possible.
An Eye for an Eye will make the whole world blind - Gandhi
Since electromagnetism is some 10^40 times stronger than gravity you wouldnt need such an incredible charge (well, relatively speaking) to influence the rotation curve of a galaxy as much as a huge amount of matter would by gravity. Also, EM diminishes by the distance squared too, so the curve would look identical.
Well, the potential energy of the EM force would then be added to the gravitational PE, making the required rotational kinetic energy less so the galaxy wouldn't rotate so fast.
Or alternatively for the same rotational velocity and kinetic energy the gravitational contribution to the potential energy would be lowered by the EM contribution, hence less mass is required.
So sure in theory that could be an explanaition, but how on Earth would a star be negatively charged? That would imply it had an excess of electrons over protons, and since both come almost exclusively from the ionization of hydrogen where would this massive excess (and it would have to be pretty big to have a noticeable effect) come from?
And again, since black holes form from stars where would their supposed positive charge come from? I personally can't think of any mechanism that would cause this sort of distinct charge difference between stellar objects. And while I'm not up on all the details, I'm pretty sure that you could tell whether a star was negatively charged through spectroscopy or some other technique.
It should be noted that this telescope will actually search for Active Galactic Nuclei (AGN), of which supermassive black holes play a small, but important role. There is alot of other really interesting physics here though! For a cool picture of an AGN, click here. For more info, click here.
Do you think they'll find the black hole that sucked away all the talent of Australian soap stars?
Why dose this dark matter exist ? Because without it the Big Bang is called into question. Of course the BB can't be wrong. We have built whole curriculums around this. It MUST be true.
You forget a possibly more important reason for dark matter to exist - in order to explain why galaxies are stable. In order for a stable, rotating galaxy to exist it must satisfy the Virial Theorem which is 2V+T=0 (I think), where V is the gravitational potential energy and T the rotational kinetic energy.
Given what we know from observations of both our own and other galaxies we can make reasonable estimates of both of these figures, using average stellar masses, the no. of stars/galaxy, the radius of a galaxy and its rotational period. What we get from these numbers is that there is only 10% of the necessary mass in the galaxies we see for them to be stable.
If there was no dark matter then the stars within galaxies wouldn't be gravitationally bound and would be flung out by the galaxy's rotation. But since we can look out to the Universe and see stable galaxies of many different ages we have to conclude that there is extra mass present in galaxies that we simply can't see. Each galaxy is embedded in a huge disc of dark matter, and without it there would be no galaxy.
Well, for one, the cost of a ground based installation is much less than a satellite, but that's the obvious answer :)
What they're doing is looking for the Cerenkov radiation produced when a high energy gamma ray from the "blazar" produced by a black hole hits the upper atmosphere. Cerenkov radiation is the product of electron/positron pair creation and bremmstrahlung and consists of relativistic particles which travel at velocities faster than the local speed of light. This results in the production of Cerenkov radiation in the blue part of the visible spectrum, which is what the telescopes actually detect.
However there is a far greater amount of Cerenkov radiation from normal cosmic ray incidents than there is from gamma rays produced in blazars. Since the cosmic ray particles are charged (they are usually protons) whereas the gamma rays aren't, they can be distinguished by whether they curve in the galactic magnetic field.
Anyway, since this is a proven technique, there's really no need for a space-based detector as of yet.