More on reionisation

Tomas Martin @ 14-12-2007

The universe has been expanding for 13 billion years

On Wednesday I talked about reionisation and how many of the new telescopes being designed are to study this side of astronomy. But what exactly does this mean? Well, ionisation just means that the electrons of an atom are separated from the protons and neutrons. This usually requires a lot of energy, especially if it occurs over a large area. When the universe began after the big bang (the far left of the picture), everything was close together and extremely hot. For a while even the quarks that make up protons and neutrons were independent of each other. Over time the universe grew and the temperature decreased. Quarks recombined into particles, electrons recombined with protons, leaving us with mostly neutral hydrogen, all across the universe.

Now, astronomers can’t see much from neutral hydrogen. It’s too cool to emit much EM-radiation as light, infra red or radio waves that telescopes can pick up. Today, however, we see lots of radiation – from stars, galaxies, black holes, quasars and ionised gas. If the universe was neutral 12 billion years ago, what caused it to reionise? Probably, the first stars caused this change. Over huge periods of time tiny variations in the density of the universe caused the hydrogen to collapse into stars, whose light then ionised the regions around them. By studying the ‘bubbles’ of ionisation so long ago we can work out why the universe has the structure we see today.

Astronomers have never seen that far back before in the key Radio and Infrared regions. The telescopes of the last fifty years just don’t have the power, as Scotty might say. The further back through time you want to look, the further the light has to travel and the fainter the signal. With the advances in computer technology over the last twenty years, we can finally start building equipment capable of seeing those first stars and galaxies. If people are interested, I’ll post the occasional update on how telescopes like JWST and SKA are progressing.

[photo by Nasa’s WMAP team via JSWT Science Case]


Reionisation and the future of telescopes

Tomas Martin @ 12-12-2007

The 42m European Extremely Large Telescope will be a feat of engineering ingenuityAs astronomers look further back in time, they need more powerful, higher resolution instruments. As well as the search for extrasolar planets, one of the key areas the new technology will be looking at is the epoch of reionisation, some one billion years after the big bang. 400,000 years after the big bang, the universe cooled enough to become opaque, so that very little light was being emitted for us to observe. Later the universe began to change and objects like stars and galaxies formed. The heat from these first objects began ionising the neutral gas of the universe, creating more stars and galaxies in bubbles of hotter regions that eventually spread to form the reionised universe we see today.

Some of the designs for new telescopes are incredible. The picture shows the E-ELT, one of the new designs of Extremely Large Telescopes (anything over 20m in diameter). The small white shape in the bottom left is a car! The awesome James Webb Space Telescope will launch in 2013 to replace the Hubble Telescope. Its mirror and tennis court-sized sunshield unfold in space once it reaches its home orbiting L2, some 1.5 Million km from Earth. ALMA, LOFAR and SKA will links tens or even thousands of smaller radio telescopes together as one massive array, stretching out across continents. The next decade will truly be a revolution in the devices astronomers use to study the sky.

[This is a version of a talk I gave as part of my masters course at Bristol University last week]