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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."
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.