Plan for instruments to create 3D map of galaxy gets funds

Plans to design instruments that will help create a 3D map of the galaxy have received £500,000 of UK funding.

The Science and Technology Facilities Council (STFC) has agreed to support the next design phase of equipment that can map the movements of one billion stars and help scientists learn more about the phenomenon of dark energy.

To do this, several international teams will attempt to develop a way of using tiny robots to rapidly position thousands of fibre-optic cables within a telescope.

The fibre optics are needed to capture sufficient light from distant stars and galaxies and feed it into a spectrometer. This will reveal how fast the waves are moving towards or away from the Earth and enable researchers to plot the movement of the source.

It will also allow them to recover patterns of sound waves from the early universe that affected the initial distribution of galaxies, in order to see how the expansion rate of the universe has changed over time.

Because the increasing speed at which galaxies are moving away from each other is thought to be driven by dark energy, this data will help scientists learn about the nature of the hypothetical phenomenon.

To gather enough data, the instruments will have to collect thousands of stars’ spectra at any one time and astronomers will need equipment that can easily rearrange thousands of optical fibres to study each area of the sky.

One of the teams is led by STFC research group RAL Space with principal investigator Dr Gavin Dalton, professor of astrophysics at Oxford University.

‘If you put a fibre down to target each one of those stars across the field of view and you feed that whole bundle of fibres back together and line it up at the entrance to the spectrograph, you can now take all of those spectra simultaneously,’ he told The Engineer. ‘So the trick is to have a nice way of moving the fibres around.’

There are several methods for positioning the fibres already in use so the researchers need to determine which would be best to scale up to deal with the thousands of cables needed.

One idea is to use thousands of tiny robots to control each fibre. A similar instrument in Hawaii that can position 400 cables in the form of ’carbon pencils’ but the new equipment would need 5,000 robots within a half-metre diameter cylinder.

‘It’s all about miniaturisation, to make them very small and compact,’ said Dalton. ‘You actually have to worry that you’ve now got 15,000 motors of some description very close to each other so they could electromagnetically interfere with each other.’

Canary Islands
One team in the STFC-funded programme is hoping to build the sky-mapping fibre-optic equipment at the William Herschel telescope in the Canary Islands

The programme will complement a European Space Agency (ESA) project to map the galaxy using an imaging satellite named Gaia, due for launch in 2013, that will track the precise position and velocity of the stars in two dimensions (up and down, left and right).

With the new equipment, scientists on Earth will be able to measure velocity in the third dimension (forward and back) by measuring the Doppler shift of the light waves — how the waves change relative to the movement of their source.

They will also be able to study the chemical make-up of stars in more detail, revealing information about how stars were originally formed in groups with similar chemistry and gradually spread out after these groups merged to form the Milky Way.

‘[The new project] can get that extra bit of information that Gaia itself can’t get, and that makes the whole data set much more useful,’ said Dalton. ‘This will be a legacy data set — people will be mining it for 20 years.’

Even with thousands of fibre optics operating over five years, the equipment will only be able to gather data on a few million stars. But this sample can then be used to build a picture of the velocity of the one billion stars Gaia is mapping.

The programme involves academics from a number of European and US universities and research institutes working in teams to develop instruments at five observatories in the Canary Islands, Chile and Arizona — although only a couple are likely to be built.