Ancient stars 1 – Simulation showing a Milky Way-like galaxy around five billion years ago when most satellite galaxy collisions were happening. Credit: Andrew Cooper / John Helly / Durham University
Ancient stars 2 – Simulation showing the stellar halo around the Milky Way in the present day. Credit: Andrew Cooper / Durham University
Many of the Milky Way’s ancient stars are remnants of other smaller galaxies torn apart by violent galactic collisions around five billion years ago, according to researchers at Durham University, who publish their results in a new paper in the journal Monthly Notices of the Royal Astronomical Society.
Scientists at Durham’s Institute for Computational Cosmology and their collaborators at the Max Planck Institute for Astrophysics, in Germany, and Groningen University, in Holland, ran huge computer simulations to recreate the beginnings of our Galaxy.
The simulations revealed that the ancient stars, found in a stellar halo of debris surrounding the Milky Way, had been ripped from smaller galaxies by the gravitational forces generated by colliding galaxies.
Cosmologists predict that the early Universe was full of small galaxies which led short and violent lives. These galaxies collided with each other leaving behind debris which eventually settled into more familiar looking galaxies like the Milky Way.
The researchers say their finding supports the theory that many of the Milky Way’s ancient stars had once belonged to other galaxies instead of being the earliest stars born inside the Galaxy when it began to form about 10 billion years ago.
Lead author Andrew Cooper, from Durham University’s Institute for Computational Cosmology, said: “Effectively we became galactic archaeologists, hunting out the likely sites where ancient stars could be scattered around the galaxy.
“Our simulations show how different relics in the Galaxy today, like these ancient stars, are related to events in the distant past.
“Like ancient rock strata that reveal the history of Earth, the stellar halo preserves a record of a dramatic primeval period in the life of the Milky Way which ended long before the Sun was born.”
The computer simulations started from shortly after the Big Bang, around 13 billion years ago, and used the universal laws of physics to simulate the evolution of dark matter and the stars.
These simulations are the most realistic to date, capable of zooming into the very fine detail of the stellar halo structure, including star “streams” – which are stars being pulled from the smaller galaxies by the gravity of the dark matter.
One in one hundred stars in the Milky Way belong to the stellar halo, which is much larger than the Galaxy’s familiar spiral disk. These stars are almost as old as the Universe.
Professor Carlos Frenk, Director of Durham University’s Institute for Computational Cosmology, said: “The simulations are a blueprint for galaxy formation.
“They show that vital clues to the early, violent history of the Milky Way lie on our galactic doorstep.
“Our data will help observers decode the trials and tribulations of our Galaxy in a similar way to how archaeologists work out how ancient Romans lived from the artefacts they left behind.”
The research is part of the Aquarius Project, which uses the largest supercomputer simulations to study the formation of galaxies like the Milky Way and was partly funded by the UK’s Science and Technology Facilities Council (STFC).
Aquarius was carried out by the Virgo Consortium, involving scientists from the Max Planck Institute for Astrophysics in Germany, the Institute for Computational Cosmology at Durham University, UK, the University of Victoria in Canada, the University of Groningen in the Netherlands, Caltech in the USA and Trieste in Italy.
Durham’s cosmologists will present their work to the public as part of the Royal Society's 350th anniversary 'See Further' exhibition, held at London's Southbank Centre until July 4th.
The highlight of their 'Cosmic Origins' exhibit is an award winning 3-D movie describing how the Milky Way formed. Visitors to the exhibit can also create their own star streams by colliding galaxies with an interactive 3-D simulation.
Andrew Cooper
[Available for interview on Tuesday 29 June and Wednesday 30 June]
Institute for Computational Cosmology
Durham University
Tel: +44 (0)191 334 3768
Email: a.p.cooper@durham.ac.uk
Professor Carlos Frenk
Director, Institute for Computational Cosmology
[Available for interview on Tuesday 29 June and Wednesday 30 June]
Durham University
Tel: +44 (0)191 334 3461
Email: c.s.frenk@durham.ac.uk
Media Relations Office
Durham University
Tel: +44 (0)191 334 6075
Email: media.relations@durham.ac.uk
Dr Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7734 3307 x 214
Mob: +44 (0)794 124 8035
Email: rm@ras.org.uk
IMAGES AND CAPTIONS
Images are available from http://www.virgo.dur.ac.uk/aquarius/ancient_stars/index.html
Images are also available on request from Durham University Media Relations Office on +44 (0)191 334 6075 or email media.relations@durham.ac.uk .
A copy of The International Virgo Consortium/Durham University Institute for Computational Cosmology “Cosmic Origins” movie is available as a MVA file via the following web link http://www.dur.ac.uk/n.s.holliman/CosmicOrigins.html
To download the file right click on the link Cosmic Origins - QHD 2D version of the 2D movie and select “save target as”. Please note this file is 257MB in size.
FURTHER INFORMATION
The work appears in the paper “Galactic Stellar Haloes in the CDM Model”, Cooper AP, et al, Monthly Notices of the Royal Astronomical Society. Doi:10.1111/j.1365-2966.2010.16740.x.
A copy of the paper is available from Durham University Media Relations Office on +44 (0)191 334 6075 or media.relations@durham.ac.uk
Institute for Computational Cosmology: www.icc.dur.ac.uk/
Durham University: www.dur.ac.uk/
Monthly Notices of the Royal Astronomical Society:
Science and Technologies Facilities Council (STFC): www.stfc.ac.uk/
Durham University – a member of the 1994 Group
Durham University is a member of the 1994 Group of 19 leading research-intensive universities. The Group was established in 1994 to promote excellence in university research and teaching. Each member undertakes diverse and high-quality research, while ensuring excellent levels of teaching and student experience. www.1994group.ac.uk
The Royal Astronomical Society
The Royal Astronomical Society (RAS: www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
