Sunday, November 11, 2007

Mysteries: Stars at Galactic Core

Once the centre of our Milky Way was a mystery. In the constellation Sagittarius, the core is permanently hidden by clouds of gas. Only very recently have radio astronomers penetrated to the core. After decades of observations they are certain that the centre is a massive Black Hole.

Equally surprising, astronomers have found thousands of stars orbiting in the core. More than 100 OB and Wolf-Rayet stars have been found that appear to have formed just a few milion years ago. Old theories of star formation can not explain how these stars exist. The immense tidal forces and radiation of the core should have torn them apart.

The Arches Cluster is in the left photo and the Quintuplet cluster to the right. The Hubble Space Telescope has found star clusters weighing 10,000 solar masses less than 100 light years from the galactic centre. These are 10 times bigger than typical star clusters in the Milky Way, exactly the reverse of what astronomers suspected. By old theories of cosmology the huge clusters should have been ripped apart.

If primordial Black Holes are involved, stars could form around them even near the galactic core. Presence of singularities would prevent the stars from breaking up. Hidden central Black Holes could also explain the massive star clusters near the core. If one Black Hole can exist in the core, why not many?



Blogger EricBourland said...

The center of the galaxy fascinates me. Thanks for this post.

4:13 AM  
Blogger nige said...

"If one Black Hole can exist in the core, why not many?"

Extending your argument further, every fundamental particle can be considered to be a black hole.

The types of Hawking radiation you get given off by charged microscopic black holes are exactly the gauge boson radiations that best describe the standard model interactions.

Here's a bit I wrote on Kea's blog about this (Kea may delete my comment for other reasons, since I'm annoying to many people like Lubos):

"The mechanism for Hawking radiation emission from a black hole is that you must have pair production near the event horizon, and one charged particle falls into the black hole (at random) while the other escapes from the event horizon. The random collection of escaping charges outside the event horizon mean that you get annihilations which create gamma rays. These gamma rays will suffer severe gravitational redshift as they escape.

"What worries me about this "physics" is that for pair production to occur near the event horizon, there must be an electromagnetic field in excess of the Schwinger threshold for pair production, some 1.3*10^18 v/m, which is a very strong field.

"Hence, it seems as if black holes must carry a large net electric charge if they are to emit any Hawking radiation at all.

"But if you have a highly charged object, then the Hawking radiation will be modified, because you will no longer have merely random particles in every pair falling into the black hole. E.g., if the black hole is positively charged, then the particles falling into it may be mainly negative, so you get mainly positive charges escaping from the event horizon.

"This actually explains the mechanism for electromagnetism by exchange radiation quite nicely: see figs. 4 and 5 of

"You just need a SU(2) group where the 3 vector bosons are not always massive, but also exist in massless forms. This works, with the massive forms of the 3 vector bosons giving the weak interaction, while the massless forms give EM and gravity. See fig. 2 of to see how charged massless radiation can propagate if it is being exchanged between charges continuously (the infinite self-inductance problem for one-way motion of massless charge doesn't exist for the same charged massless radiation going in opposite directions, because each vector cancels the B-field of the other!).

"Of course, to a mathematician who doesn't care about physical mechanisms, my concern here (and particularly, my constructive demonstration of how to solve these problems) is a load of embarrassing, loony, crackpotism.

"It's possible that Lubos's paper is relevant to physics. The gauge boson exchange radiation of quantum electromagnetic forces and quantum gravity need to be considered as special kinds of Hawking radiation, and all fundamental particle cores need to be considered to be special (charged) types of black hole.

"In my opinion it is loony, etc., not to investigate this carefully. However, the Middle Age attitude of worshipping published long-standing experts like Aristotle over newfangled ideas based on facts, is with us. Truth isn't always quite as popular as the hyped up stringy stuff."

2:22 PM  
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