How University of Cambridge astronomers looked back 12.9 billion years - and detected motion in newborn galaxies
Dr Renske Smit of the Kavli Institute of Cosmology explains how they used ALMA, the world's most expensive land-based telescope
They have peered back in time… and they were amazed at what they found.
University of Cambridge astronomers used the most expensive ground-based telescope in the world to probe some of the earliest galaxies in the universe.
Looking back nearly 13 billion years to a time soon after the Big Bang, they were able to detect swirling gas in two ‘newborn’ galaxies.
It is the first time that movement has been detected at a point so early in the history of the universe – a time of great turbulence.
Despite that, the international team of researchers led by Dr Renske Smit, from the Kavli Institute for Cosmology at Cambridge, found something familiar and even orderly – whirlpool motion like our own Milky Way.
Speaking to the Cambridge Independent shortly after presenting her findings to the 231st meeting of the American Astronomical Society in Washington, Dr Smit said: “We originally started with images from the Hubble Space Telescope and the Spitzer Space Telescope and we identified really interesting candidate galaxies.
“We wanted to measure how early in time we were seeing these galaxies. That’s why we asked for data from ALMA.”
Comprised of 66 radio telescopes, 12 metres (39ft) and seven metres (23ft) in diameter, the Atacama Large Millimeter/submillimeter Array, or ALMA, was built at an altitude of 5,000 metres (16,000ft) on the Chajnantor Plateau in northern Chile at a cost of $1.4billion to partners around the world.
The research team used ALMA to observe the small newborn galaxies as they existed 800 million years after the Big Bang.
This is possible because light from distant objects takes time to reach Earth, meaning that we effectively look back into the past when observing objects in space.
But the early universe was filled with a haze of neutral hydrogen gas that makes it hard to see with optical telescopes.
ALMA, however, can probe the dark universe in a way that other telescopes cannot.
Its 66 antennas work together as if they were a single giant telescope using a technique called interferometry. Together, the antennas pick up signals and join forces to uncover the source of emission, whether it is a star, planet or galaxy.
While optical telescopes pick up visible light, ALMA analyses radio waves to examine the weakest signals in space – those with the lowest energy.
Combining these radio waves, ALMA can deliver very high-precision images. To achieve the same with one telescope, its diameter would need to be equivalent to the furthest distance between the antennas – 16 kilometres in ALMA’s case.
“You need to design exactly what frequency, what resolution and how long you want to look,” said Dr Smit. “There are a lot of parameters and you need to get them all right. There have been less successful observations because it’s a really complicated instrument but at least they were published, so we knew what not to do!”
Analysing the spectral ‘fingerprint’ of the far-infrared light collected by ALMA, the research team was able to establish the distance to the galaxies and witness the internal motion of the gas that fuelled their growth.
“The measurements we were hoping to make was the look-back time – it gave us 12.9 billion years. That told us this was 800 million years after the Big Bang.
“That’s already a really difficult measurement to make,” said Dr Smit.
“We didn’t know that the data would be good enough to give us what was the most exciting part of this discovery – that we were able to look at the motion of the gas.
“ALMA gave us higher resolution images than we asked for. We were able to resolve it and see the details inside the galaxy. That was exciting – we didn’t expect that.”
The galaxies were found to spin like a whirlpool, similar to our own Milky Way and other more mature galaxies – a big surprise for the researchers.
“We expected the gas to be very chaotic. In the early universe, gravity caused gas to flow rapidly into the galaxies, stirring them up and forming lots of new stars – violent supernova explosions from these stars also made the gas turbulent,” explained Dr Smit, a Rubicon fellow at Cambridge, sponsored by the Netherlands Organisation for Scientific Research.
“We expected that young galaxies would be dynamically ‘messy’, due to the havoc caused by exploding young stars, but these mini-galaxies show the ability to retain order and appear well regulated. Despite their small size, they are already rapidly growing to become one of the ‘adult’ galaxies like we live in today.
“We don’t yet know what it means but we’ve asked for more data from ALMA based on these observations. One thing we need to do is look for more galaxies – are these two exceptional?”
Despite being about five times smaller than the Milky Way, these two formed stars at a higher rate than other young galaxies.
“Young galaxies are like young children… they grow as you look at them!” said Dr Smit. “These ones in particular are forming a lot of new stars so essentially these are very rapid growers – that may be why we’re seeing the disc-like structure.
“We’ve seen this three billion years after the Big Bang. But those galaxies have had a few billion years to evolve – so maybe these evolved very rapidly.
“A lot of things in the universe are disc shaped because of the conservation of angular momentum – the physical laws – so as long as a galaxy is not disrupted too much it will form a disc.”
The researchers know that carbon is present along with hydrogen and helium – the gases produced by the Big Bang – but the precise composition of these galaxies is not yet clear.
The study, reported in the journal Nature, paves the way for larger studies on galaxies in the first billion years of cosmic time.
The work was funded in part by the European Research Council and the UK Science and Technology Facilities Council (STFC).
Dr Renske Smit will give a free public talk about her work at 7.15pm on Wednesday, February 21 in the lecture theatre in the Hoyle Building at the Institute of Astronomy, off Madingley Rise in Cambridge. Public open evenings are held at the insitute throughout the year. Groups of more than 15 should pre-book. Visit the Institute of Astronomy website for more.