The evolution of galaxies is one of the the great outstanding mysteries of astrophysics. And in recent years, astronomers have taken great strides in tackling the problem.
The latest generation of telescopes peer back in time to within a few hundred million years of creation. They clearly show the first galaxies shining brightly only 600 million years after the Big Bang. These galaxies form clusters which themselves stretch out across the cosmos in a vast filamentary-type structure known as the cosmic web.
This structure corresponds more or less exactly to the differences in the density of matter that must have arisen in the instants after creation. Cosmologists think they understand this structure well and have accurately simulated how it came into being.
The only wrinkle in their models is the stars from which galaxies are made, which must obviously have formed earlier.
Astronomers think that earliest stars must have switched on about 30 million years after the Big Bang. And that raises an interesting question: how were these stars distributed through the universe at that time?
This problem is not as straightforward as it sounds. It’s easy to imagine that since the galaxies formed from the coalescence of stars, their distributions must be similar.
But astronomers have recently discovered a problem with this line of thinking. Galaxies appear to have formed around massive haloes of dark matter.
But that can’t be the case for stars. In the early universe, visible matter would have been accelerated by radiation pressure while dark matter was not. So the earliest stars must have formed from stuff that was moving too quickly relative to the dark matter background to be captured by it. And that means the distribution of the first stars would have been significantly different from the later distribution of galaxies.
Now Eli Visbal at Harvard University and a few pals have performed the first detailed simulation of this effect to create map of the earliest stars. This map of the universe when it was just 30 million years old shows that the universe’s earliest occupants must also have formed a cosmic web of their own, albeit different in structure from the one we see today.
Although this is only a simulation, we’re likely to find out soon how good it is. The first stars produced light that we ought to be able to see today and a global effort to spot it is currently underway.
Astronomers have built a number of telescopes capable of seeing this light, which is now redshifted into low-frequency radio waves. Observatories such as the Murchison Widefield Array, the Low Frequency Array for radio astronomy (LOFAR) and the Giant Metrewave Radio Telescope will look for light from the oldest stars and eventually show us how accurate this type of simulation can be. We’ll see the results in the next few years.
Ref: arxiv.org/abs/1201.1005: The Grand Cosmic Web of the First Stars