Using artificial intelligence to chart the universe
Scientists routinely use large telescopes to scan the sky, mapping the coordinates and estimating the distances of hundreds of thousands of galaxies and so enabling scientists to map the large-scale structure of the Universe. But the distribution they see is intriguing and hard to explain, with galaxies forming a complex ‘cosmic web’ showing clusters, filaments connecting them, and large empty regions in between.
The driving force for such a rich structure is gravitation. Around 5 percent of the cosmos appears to be made of ‘normal’ matter that makes up the stars, planets, dust and gas we can see and around 23 percent is made up of invisible ‘dark’ matter. The largest component, some 72 percent of the cosmos, is made up of a mysterious ‘dark energy’ thought to be responsible for accelerating the expansion of the Universe. This Lambda Cold Dark Matter (LCDM) model for the universe was the starting point for the work of the Potsdam team.
Measurements of the residual heat from the Big Bang – the so-called Cosmic Microwave Background Radiation or CMBR – allow astronomers to determine the motion of the Local Group, the cluster of galaxies that includes the Milky Way, the galaxy we live in. Astronomers try to reconcile this motion with that predicted by the distribution of matter around us, but this is compromised by the difficulty of mapping the dark matter in the same region.
“Finding the dark matter distribution corresponding to a galaxy catalogue is like trying to make a geographical map of Europe from a satellite image during the night which only shows the light coming from dense populated areas”, says Dr Kitaura.
His new algorithm is based on artificial intelligence (AI). It starts with the fluctuations in the density of the universe seen in the CMBR, then models the way that matter collapses into today’s galaxies over the subsequent 13700 million years. The results of the AI algorithm are a close fit to the observed distribution and motion of galaxies.
Dr Kitaura comments, “Our precise calculations show that the direction of motion and 80 percent of the speed of the galaxies that make up the Local Group can be explained by the gravitational forces that arise from matter up to 370 million light years away. In comparison the Andromeda Galaxy, the largest member of the Local Group, is a mere 2.5 million light years distant so we are seeing how the distribution of matter at great distances affects galaxies much closer to home.
Our results are also in close agreement with the predictions of the LCDM model. To explain the rest of the 20 percent of the speed, we need to consider the influence of matter up to about 460 million light years away, but at the moment the data are less reliable at such a large distance.
Despite this caveat, our model is a big step forward. With the help of AI, we can now model the universe around us with unprecedented accuracy and study how the largest structures in the cosmos came into being.”
Since 2011 Francisco Kitaura has been working at the AIP. His publication is available online on http://arxiv.org/abs/1205.5560 and will soon be published in Monthly Notices of the Royal Astronomical Society (MNRAS).
Image #1 (above): Supergalactic plot of the Cosmic Web Structure
A slice through the three dimensional Local Universe with side 370 Million light years is shown. The red circles represent observed galaxies from the 2MRS survey. The blue circles are random galaxies filled in the so-called zone of avoidance, where the stars of our Milky Way do not permit us to observe extragalactic sources. The light and dark colour code stands for the density field reconstruction using the KIGEN artificial intelligence code showing the cosmic web matching the distribution of galaxies.
Image #2 (right side): Sky plot of the Comic Web Structure
The projected density field on the sky up to distances of about 185 Million light years distance obtained by the KIGEN code from the 2MRS data is shown.
Dr. Francisco-Shu Kitaura, +49 331-7499 447, firstname.lastname@example.org
Research, Images, Movies: http://www.aip.de/Members/fkitaura
Dr. Gabriele Schönherr / Kerstin Mork, +49 331-7499 469, email@example.com
The key topics of the Leibniz Institute for Astrophysics are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. Since 1992 the AIP is a member of the Leibniz Association.