Comments on: Glob smacked

By: Bookmarks about Anthropology

Bookmarks about Anthropology — Wed, 17 Dec 2008 02:31:17 +0000

[...] – bookmarked by 5 members originally found by meneldis on 2008-11-07 Glob smacked http://blogs.discovermagazine.com/badastronomy/2008/08/05/glob-smacked/ – bookmarked by 2 members [...]

By: Eric

Eric — Wed, 27 Aug 2008 09:51:37 +0000

Phil – nice summary of the science! I know this is a bit late, but I just found this thread. Regarding the question of why the survey found 11,000 globular clusters in the entire galaxy cluster whereas M87 alone has 13,000, the answer has to do with the number of galaxies in the survey and the field of view of Hubble.

We actually only looked at 100 of the over 2,000 galaxies in Virgo. Also, the field of view of the camera we were using (the Advanced Camera for Surveys) is sufficiently small that for large galaxies like M87, we only measure a fraction of the total population of globulars. We know from other observations and that M87 has ~13,000, but we only directly observed around 1,000 with HST.

Keep up the good work!

By: Torbjörn Larsson, OM

Torbjörn Larsson, OM — Thu, 07 Aug 2008 02:24:04 +0000

I always thought we (the Milky Way) were part of the Local cluster, or the Local group, wich in turn was part of the local supercluster, or the Virgo supercluster.

Me too.

So, to the experts – what is wrong with that picture?

Im sorry…black holes evaporate? does anyone have proof to substantiate this?

Um, we had that question a few threads back. It comes out of GR research in the 70’s.

I’m not conversant with GR. But AFAIU there are two ways that black holes may loose energy on, and so evaporate.

The first way is to extract mass-energy from excited black holes. (Black holes are dynamic objects with mass, momentum, angular momentum and charge.) Let me cite the old GR bible (”Gravitation”, Misner, Thorne, Wheeler; also called “MTW” for short):

“A Kerr-Newman black hole – which is rotating or charged or both – is not dead. The rotational and electromagnetic contributions to the mass-energy can be extracted.”

So first you have the gravitational radiative dynamics of a freshly collapsing black hole. Then it starts to stabilize it can continue to leak off energy as a Kerr-Newman black hole by being perturbed by the environment, say an accretion disc, until it is a “dead” Schwarzschild (non-rotating, non-charged) black hole.

The second way is through Hawking radiation, which Hawking established as a possibility by physics, not by “say so” obviously. I assume string (brane) models can give the same results. And finally I assume that the final evaporation of black holes are not well understood. (That, I believe, is one of the uncertainties of LHC detection of the same.)

I believe none of these ways are experimentally proven by direct observation. But there are ongoing attempts to use optical systems to simulate the event horizon of black holes to possibly observe analogue processes.

By: Daniel

Daniel — Wed, 06 Aug 2008 23:28:24 +0000

Wait. Im sorry…black holes evaporate? does anyone have proof to substantiate this? (and just because Steven Hawking says doesnt count) talk about woo.

By: DrFlimmer

DrFlimmer — Wed, 06 Aug 2008 17:52:04 +0000

Pouria,
Hawking radiation is when a pair of “virtual particles” are created very close to the event horizon. What are “virtual particles”? The vacuum of space is not “empty” or a place of “no” energy. There is a vacuum-energy. And due to “E=mc^2″ a particle and it’s anti-particle can be created “out of nothing”. They annihilate each other again, so nothing has really happened. That’s why they are called “virtual”.
If they are created very close to the event horizon of a black hole one of the particles can fall in before they annihilate and the other is left behind and becomes real. But, the two particles have “stolen” their energy from the vacuum-energy of space which would be against the law of energy-conservation. So the energy is taken from the black hole which ate one particle but it must give back the “mass-energy” of TWO particles, so it looses ernergy and so mass.

But: The particles in the jet are not massless. You can have electrons, protons, positrons, etc in such a jet with incredibly high speeds – as I said before, they are very closed to the speed of light. The particles do NOT come OUT of the black hole but from it’s accreation disk. But how they are accelerated to such speeds is still a mystery, as I also said before.

By: SteveG

SteveG — Wed, 06 Aug 2008 17:04:17 +0000

So globular clusters of stars are like little tiny galaxies, which are part of other galaxies, which are part of galaxy groups, which are part of galaxy clusters.

My head hurts.

By: DrFlimmer

DrFlimmer — Wed, 06 Aug 2008 14:51:39 +0000

Edward,
the stream is called a “jet”. It’s a thin tube of a magnetic filed. Through this tube rush charged particles (electrons, positrons, protons, etc) at nearly the speed of light. How this particles are accelerated is still a mystery. It’s likely that magnetic field lines of the accreation disk (the disk of particels surrounding the black hole before they fall in) are connected in some way with the jet-field lines and stripe away some particels. But they get that fast remains unknwon.