The first building blocks of the universe

May 13, 2014

The first galaxies evolved only a few hundred million years after the Big Bang. But why do they have such a great variety of shapes and structures? How did the universe evolve as a whole? Two German-Chinese Partner Groups at the Max Planck Institute for Astrophysics in Garching are using observations and simulations to investigate how the early universe evolved: Cheng Li and Guinevere Kauffmann, as well as Liang Gao and Simon White.

This changed only when the researchers also looked at data from the Wide-Field Infrared Survey Explorer (WISE), an American infrared telescope. “Significant differences were evident when the visible and the infrared images were compared,” says Li. It appears that galactic collisions create large numbers of new stars, whose dust hides the active galactic nuclei in the visible light – and this had initially led to incorrect conclusions being drawn.

The group around Liang Gao studies the dark matter, which makes up for 24 percent of space.

Li and Kauffmann have also turned their attention to even longer wavelengths: radio emission. With a diameter of 30 meters, the telescope of the Institute for Radio Astronomy in the Millimeter Range (IRAM) in South Spain is able to analyze not only atoms, but also molecular gas in distant galaxies. Likewise, the Arecibo telescope in Puerto Rico has remained the largest radio telescope in the word for more than three decades capable of surveying atomic gas with a temperature of 10,000 K.

“Radio telescope technology lags far behind that of optical telescopes, so this gas is difficult to observe. But it is also more closely connected to accretion from the external birth of new stars,” explains Li. He and his colleagues observed around 800 galaxies and the results have been published in a series of joint papers.

Around 1000 kilometers further north, at the National Astronomical Observatories near the Beijing National Stadium, Liang Gao is working on a cosmic phenomenon which is even more difficult to make out: dark matter. Gao and Simon White, his colleague from Garching, head the second Chinese Partner Group of the Max Planck Institute; instead of observations, they rely on computer simulations.

Simulation on the computer: The image is from the Phoenix project and shows a rich cluster dark matter halo which is simulated with 1.3 billion particles. The length across is 23 million light years on a side.

Dark matter is a good candidate for this: According to the current standard model of cosmology, it accounts for 24 percent of the universe; normal matter accounts for just below 5 percent, the rest is what astronomers call dark energy. Dark matter is invisible; however, it betrays itself only indirectly – for example by slightly deflecting the light from distant stars. “This is how we know that dark matter interacts with other matter only via gravity,” says Gao. “This makes it relatively easy to simulate, even if we don’t yet know its true nature.”

Gao uses his computations to investigate how matter could be distributed in galaxy clusters, among other things. Moreover, he wants to assist other astronomers to check their theories on the strange substance – and thereby finally come closer to the exact nature of dark matter. One of these theories predicts, for example, that the building blocks of the unknown matter destroy each other under certain conditions. Gamma radiation should be released in this process, and particularly large amounts in the centre of galaxies such as the Milky Way. Observers have still been unable, however, to observe anything.

Using a simulation which ran for four months on a supercomputer at the Chinese Academy of Sciences, Gao and his colleagues searched for regions in the universe where the reception of this signal should be better. Their result: Galaxy clusters in the close vicinity of the Milky Way could be a good place to find traces of dark matter – if the giveaway gamma radiation exists at all.

As the next step, Gao and White want to expand their computer simulations even further. The astronomers want to get a step closer to the mystery of dark energy on the Chinese supercomputer Tianhe-2, currently the fastest in the world. It will be, says Gao, the largest cosmological simulation the world has ever seen. First results are expected in summer 2014.

The Partner Group also has big plans in Shanghai. FAST, the Five Hundred Meter Aperture Spherical Telescope, is currently being built in Guizhou Province in South China. With a dish diameter of 500 meters, it will be the largest radio telescope in the world - perfect for an unobstructed view into distant galaxies. And in southern Africa and Australia preparations are underway for the Square Kilometre Array (SKA), a link-up of radio telescopes which together will have a combined dish area of one square kilometer.

The German and Chinese cosmologists are involved in both projects. “These telescopes,” says Cheng Li, “will finally make it possible for us to investigate the gas in near and more distant galaxies in more detail.”



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