Astronomy Now Home
Home Magazine Sky Chart Resources Store

On Sale Now!



The September 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). The Astronomy Now iPad/iPhone editions are now available worldwide on the App Store.



Top Stories



Earthshine used to test life detection method
...By imagining the Earth as an exoplanet, scientists observing our planet's reflected light on the Moon with ESO's Very Large Telescope have demonstrated a way to detect life on other worlds...
  READ MORE

Solid buckyballs discovered in space
...Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time...
  READ MORE

Steamy water-world gets the Hubble treatment
...Hubble Space Telescope observations of a 7 Earth-mass planet find an unusual water-rich world swathed in a thick, steamy atmosphere...
  READ MORE








First simulation of a
Milky Way-like galaxy

by Phil Unsworth
for ASTRONOMY NOW
Posted: 31 August 2011


Bookmark and Share

A team’s efforts to create a computer simulation of a Milky Way-like galaxy is reported as successful, and helps to solve a recurring problem of galaxy formation.

Over the past twenty years various attempts have been made to recreate our own Galaxy in computer simulations, but have failed due to the complexity of the Milky Way’s composition, including the central bulge of stars, and the surrounding characteristic spiral arms. A new simulation named “Eris”, conducted using NASA’s state-of-the-art Pleiades supercomputer (along with supporting simulations from University of California Santa Cruz, and the Institute For Theoretical Physics, Zurich) has changed that, by modeling characteristics including brightness, stellar content, and the bulge-to-disc ratio.


On the left is Eris, as shown after 13 billion years. On the right is M74; a spiral galaxy similar to the Milky Way. Both are coloured to show gas clouds in red and stars in blue. Image: University of Zurich & NASA.

“Previous efforts to form a massive disc galaxy like the Milky Way have failed because the simulated galaxies ended up with huge central bulges compared to the size of the disc,” says Javiera Guedes, lead author of the paper describing the new simulation, which took nine months to process. “The simulation follows the interactions of more than 60 million particles of dark matter and gas. A lot of physics goes into the code, and this is the highest resolution cosmological simulation ever done this way.”


The top images shows the simulated galaxy Eris, as seen in the galactic plane. The lower image shows a similar view for the Milky Way, as taken in the infra-red by 2MASS. Both show the smaller bulge in comparison to the extending spiral arms. Image: 2MASS, Callegari & Guedes.

Dark matter, so called because it is so-far unseen in observations, and thought to comprise at least 80 percent of the matter in the Universe, is the main drive behind the prevailing theory of how structure in the Universe arose. Fluctuations in the dark matter density shortly after the big bang resulted in small clumps being pulled together by gravity. These small clumps then merged into larger and larger clumps with ‘normal’ matter falling into the gravitational wells created by the dark matter, resulting in galaxies sat within dark matter haloes. Given that the dark matter is thought to outnumber the normal matter, this has led to the “cold dark matter theory”, where structure in the Universe is driven by dark matter’s gravitational interactions.

“The simulation shows that the cold dark matter scenario, where dark matter provides the scaffolding for galaxy formation, is able to generate realistic disc-dominated galaxies,” says co-author Piero Madau, also of UCSC.

Along with the high density regions distributing star formations more accurately, the simulations also better reflect the behaviour of supernovae. In the high density regions, the exploding supernovae energy blows gas out of the galaxy, where it would otherwise accumulate and add to the central bulge. “Clustered star formation and energy injection from supernovae are making the difference in this simulation,” says Madau.

The team’s paper has been accepted for publication in The Astrophysical Journal.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.
 GET YOUR COPY

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
 GET YOUR COPY

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
 GET YOUR COPY


HOME | NEWS ARCHIVE | MAGAZINE | SOLAR SYSTEM | SKY CHART | RESOURCES | STORE | SPACEFLIGHT NOW

© 2014 Pole Star Publications Ltd.