Black Holes, Galaxies & Stars

Now that much of the inferred population of the universe's black holes has been found the overall picture seems to be like this.

In their youth, galaxies form stars and black holes together as the primordial gas and subsequently added dust (you don't get dust until the first generation of supernovae have gone pop and spilled their heavier elements - "metals" in astronomical terminology). The black holes at the centres of galaxies grow until they become quasars and the intensity of their own radiation holds back the very material they need to grow further, which leads to the general observation that central black holes are typically about 0.2% of galaxy mass (I think that's the right figure).

[Side note - now we have found the hidden population of black holes, we can infer something about quasar structure by comparing the numbers we can see directly with those we see indirectly through the infra-red etc. from surrounding dust.]

If this picture is broadly correct, then there should be a typical upper mass-limit for organically grown black holes.

My conclusion from all this: central black holes of greater mass should be indicative of galactic mergers and the mass of such holes might even be a proxy for the number of mergers that have occurred in the course of a particular galaxy;s history (complicated of course by the original size of the galaxy cluster etc.). It is interesting to consider that, whilst the specifics would always remain vague (barring identification of specific sub-populations of stars by e.g. velocity, age, etc. - we can do this for the Milky Way, and have found the remnants of several mergers this way, but it becomes increasingly difficult the further away a target galaxy is), one might be able to infer something about the original sizes of clusters, super-clusters etc. in the early universe from present day observations; or, running the logic in reverse, the more we learn about early cosmological structure, the more we may be able to infer about the dynamics of galactic mergers.

Just a thought. Just more Stuff.

The Dogon of Mali, Sirius and Stuff

Here is a Dogon joke:

Q: How many people are there in a Dogon family?
A: Five - two parents, two children and a French anthropologist.

Anthropologists just love the Dogon - and why not, they are a fascinating people - Mali is on my list of Must-See places as soon as IT is finished and I reap the reward of some hard earned globe-trotting (No, you may not go first Dean - I mentioned Namibia once and the next thing I know he's swooping over the desert at head height in a light aircraft!).

Anyway, the Wikipedia article is rather long on the whole "Sirius Mystery" angle: how come the Dogon know so much about Sirius - and even the existence of Sirius B which you need a pretty large telescope to see, etc. etc. eh?

Unfortunately, no one is without a reasonable argument: they learned all about Sirius from aliens (who, after all, should be expected to know) or they learned about it from missionaries - the god-bothering brigade of olden days, being gentlemanly in their pursuits, being rather keen on the whole astronomy thing don't you know?

However, I digress... but before returning to the topic, where did I hear that the Dogon also talk of Sirius C - whose existence wasn't detected until a very few years ago? Hmmm? Are missionaries now providing real-time hookups to Hubble as they go? [Found it: le Renard Pâle, p475... "The star emme ya” emme ya tolo is more voluminous than po tolo and four times lighter. It also orbits around Sirius...]

Anyway, what the Wikipedia article doesn't mention are some other, y'know, like "wow!" things the Dogon believe in... if you put the right spin on them.

This came home to me as I was reading Essai sur las Cosmogonie des Dogon a book by a French anthropologist (see?) called Eric Geurrier, which also references the seminal work mentioned above, "Le Renard Pâle" by Marcel Griaule and Germaine Dieterlen, 1965 (guess their nationality and occupation!).

According to this, the Dogon speak of le "monde d’étoiles en spirale" - the spiral word of stars - which sounds remarkably like a galaxy to me... furthermore, they don't just speak of Le Monde, they speak of Les Mondes, a veritable plethora of galaxies.

But, they are not merely masters of the macrocosm, they are pretty good on the microcosm too... this is the (heavily edited and badly translated by me) story of creation:

In the beginning, before all things, was the god Amma, who rested on nothing. The rolled-up ("en boule") egg of Amma was closed [in upon itself], but divided into four pieces called “clavicles”

The four clavicles are equally prefigurations of the four elements the “four things” water, air, earth and fire; similarly the bisections which separated them, marked the four collateral directions the “four angles”, which is to say, space

But Amma was not very pleased with the result, so he started again...

‘Oeuf D’Amma” Second Genesis (again my translation from the French)

He opened his eyes. This act caused the emergence of the yala from the spiral which, turning in the egg prefigured - in the interior of the egg - the future expansion of the universe.

Thus Amma had pierced the envelope of his breast, and his “eye”, appearing as if from a hole, had become a light, which lit up the universe and revealed the existence of all things in creation.

The universe in the breast of Amma was timeless and without extent, space and time merged by mutual agreement.

When I read this, I was astonished to find myself contemplating the very creation of space and time, their intrinsic inter-connectedness, the Big Bang, etc. etc. described in mythic terms by the Dogon. [If only I could track down the article I read once in which somebody brilliantly re-wrote modern particle physics as a piece of wizardry on a par with Lord of The Rings]

But, enough about Sirius already- lets big-up the Dogon for their whole intuitive appreciation of Special Relativity, General Relativity, cosmology, the Big Bang, etc. etc. and come to think of it, the whole en-boule thing which is really about Grand Unification of the four forces, possibly even, via the "chevron dance", anticipating String Theory.

Can I make this an urban myth? Nope - that's up to you!

PS French anthropology is great! You should read "The Raw and the Cooked" (Le Cru et le Cuit) by Levi Strauss - he has a wonderful transformational theory that can explain everything.