In several clips available on youtube (including the one below from the American Museum of Natural History) people have brought together the vast distances routinely seen in astronomy in order to give an idea of how one scale relates to the next. The result in each case is a glimpse of the enormity of the observable universe.
In that clip, just before the cosmic microwave background, loads of dots representing quasars are seen. Quasars, or quasi-stellar objects, are active galactic nuclei – enormous black holes gobbling the matter around them as fast as they can. The huge energies involved in putting together such a meal as would overwhelm even the greedy gaping maw of a black hole results in incredible amounts of radiation being emitted. This leaves quasars as the brightest things we can see. So bright that they can be seen over distances greater than any other object, providing a probe into the early universe that existed as they were being formed.
The reason why the universe had such nasty star eaters back then, but not so much as a dim glow in the centre of most galaxies where the same monsters still roam now is that back then, there was so much more gas about everywhere. A smorgasbord for the black holes to feed on. Now everything’s expanded out a bit, some parts have clumped into stars and there isn’t much left. Where once matter lived its life out as atomic hydrogen, one proton, one electron, now massive dust molecules hold in dozens of baryons and electrons in one point. And as the number of particles generally available fell, the black holes took those around them, with nothing replenishing them.
This hypothesis leads us to the idea that in the far distant past, there was a time when the black holes were free from dust around them. I reported yesterday on the Planck telescope mapping the sky in terms of the amount of dust within 500 light years, using its spectrum to identify it. In the same way, the Spitzer space telescope studied 21 distant quasars and found two of them had seemingly had a spring clean – they were totally dust free. J0005-0006 and J0303-0019 and the furthest away of the quasars spotted by the Sloan Digital Sky Survey (which provides the galaxies in Galaxy Zoo). The follow up observations using Spitzer showed that unlike more massive, older quasars, these ones didn’t have a ring of dust around them that creates an increase in infrared radiation at some wavelengths (see graphic below). However, like the massive black holes, Spitzer is now past its best, running without coolant and so unable to operate in the wavelengths this work needs. To find other dust free quasars, the astronomers will have to wait for the James Webb Space Telescope to come into operation.
But that isn’t all that’s been making the news today. The Dark Flow is an interesting mystery. A massive region of space in which all objects appear to be moving to a certain area. The data has been checked and rechecked many times over, but it appears that this is a real thing, not an observational artifact. A recent paper has analysed how light from the cosmic microwave background is scatter by galaxy clusters, a little like seeing how starlight is scattered by the bubble of atmosphere round the Earth. The result isn’t a nice clean round bubble, but a flow headed towards the constellations of Centaurus and Hydra.
There are a number of theories abounding about the Dark Flow – could it be an inhomogeneity in the big bang or inflation that is simply collapsing? Could the universe be a shape other than that we assume? – one interesting one is that the Universe is a part of a larger structure and we’re either expanding into something that then exerts gravitational forces on us or there’s another sibling universe doing the same. This wouldn’t bode well for one of the tenants of General Relativity – that gravity is the result of the curvature of space-time induced by objects lying within it – as space-time shouldn’t extend beyond the universe itself. String theory relies on a particle solution to gravitation, but the predicted behaviour of gravity is at odds with observations. Instead it is hypothesised that gravity acts through several dimensions as well as space-time and this lessens the effect we feel – ie it loses most of its particles so acts like a weaker force. String theorists would therefore hope that this is the action of another universe, possibly through these other dimensions, alerting us to the presence of structure beyond that we can otherwise see.
My view? We’re a little out of my area, so I’ll just nod sagely and hope it all goes away.