British astronomers have finished building a cosmic time machine to discover how the earliest galaxies formed and developed at the dawn of the universe. KMOS, the most complex instrument of its kind ever assembled, at a cost of £15 million, will peer back more than 13 billion years to see the first stars switch on in the darkness that followed the Big Bang.
Weighing eight and a half tons, it will be shipped out from Edinburgh to be bolted to the side of a giant telescope in the VLT array at Paranal in Chile and be able to pick out and study dozens of remote galaxies at a time.
They will be so far away that their light is too faint to see visually. But by staring at one patch of sky at a time for hours or even nights on end, KMOS – the K-band Multi-Object Spectrometer – will collect enough photons to learn all about them.
Previously, astronomers have had to pick out an individual faint fuzzy blob in photos from the Hubble space telescope and then determine its distance by checking the red shift of lines in a spectrum of its light.
KMOS has 24 supercold robotic arms that will observe 24 galaxies at once in a live view of the heavens seven arc-minutes wide – around a quarter the diameter of the moon in the sky. Clever software will help pick each target and stop the arms colliding with each other.
An image of each galaxy will be sliced and diced and fed through one of three spectrometers to give a 3D picture. Feeble photons of light that have spent 13 billion years racing across the void of space will reveal what each galaxy is made of and how it is spinning.
The revolutionary technique will help lift the veil from a mysterious time just a few million years after the Big Bang called the reionization epoch. That will help astronomers discover how galaxies evolved to become the cosmic islands we see today.
Skymania News was invited to Edinburgh to see KMOS before it departs for Chile. Systems engineer Phil Rees, who led the team building KMOS at the Astronomy Technology Centre in Edinburgh, told us: “For every pixel in the image, you’re getting the composition of the galaxy, the chemical elements in it, and also its velocity, so you can see how it is moving, how it is spinning, if bits are flying out of it and what they’re made out of.
“So it is giving you an incredible amount of information. It’s not just a picture of a galaxy, it is giving you a really detailed analysis of what’s happening there and then the clever guys try to work out what it actually means.”
KMOS contains more than 1,500 tiny, diamond-cut, gold-plated mirrors and will be chilled to a temperature of 100 degrees Kelvin (-170 C) to work at infrared wavelengths of light, using 56 separate cryogenic mechanisms. The intense cold, produced using liquid nitrogen then helium, is necessary to prevent the warmth of the apparatus from interfering with the faint signals from space. It will take a week to cool down to the required temperature.
The UK and Germany have each put £7.5 million into building KMOS for the European Southern Observatory. Six institutions were involved in its construction including the universities of Durham, Oxford and Bristol in the UK. It was assembled and tested at the ATC, which is part of the Science and Technology Facilities Council and based at the Royal Observatory Edinburgh.
The detectors, originally developed by the US military, pick almost single photons. Mr Rees said: “We get sent the best because the military don’t need such high spec. But we pay a premium. They are very expensive.”
He added: “Everything is cut to extremely high tolerances. We actually use sub contractors who are used to working with Formula One engines. It is very high-precision engineering. Because you can’t lubricate any of the mechanisms – their operating temperature is too cold – you have to ensure that the tolerances, the separation between all the components is extremely accurate so that you don’t get excessive wear when the things are moving.”
The biggest part of KMOS is a giant ring that surrounds the detectors. That will prevent the myriad of cables from getting tangled when the telescope turns to follow the stars as the Earth rotates. That “cable tidy” will take six weeks to travel by ship to Chile while the rest goes by air before both are carried across the Atacama Desert to the Very Large Telescope at Cerres Paranal. There KMOS will be fitted to VLT-1, named Antu after the native indian name for the Sun, with its huge 8.2-metre wide light-gathering mirror.
Astronomer Michele Cirasuolo, instrument scientist for KMOS in Edinburgh, said: “Until now you could only observe one object at a time. It was really time consuming. If you wanted to observe a large number of galaxies it would take years. That’s why KMOS is really needed.
“If you look at the local Universe, you see a lot of dark galaxies, some of them are round elliptical galaxies, some of them are spirals, some of them are still forming and some of them are dead. So we see them but we don’t know why they are like that. But if we go back in time you can trace them as they start forming, merging and assembling their stars.
“The second half of the Universe has been well studied by examining spectra of the nearer galaxies. But we are missing the first half and we need to look at the near-infrared light to see what the most distant galaxies are made of. To observe one galaxy at a time would be very time-consuming. By studying several at a time we can make a survey and have a proper statistical study.”
“A previous first-generation instrument, SINFONI, has been observing one galaxy at a time and in five or six years has observed 150-200 objects. KMOS will do that in a couple of months.”
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