Astronomy Now Home
Home Magazine Resources Store

On Sale Now!

The October 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). Astronomy Now is the only astronomy magazine specially designed to be read on tablets and phones. Download the app from Google Play Store or the Apple 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...

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...

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...

New stellar streams discovered in Andromeda
Posted: 28 January 2010

Bookmark and Share

New stellar streams observed in the halo of nearby galaxy Andromeda that show an intensification of the density of stars represent the tell tale signs of past galactic collisions.

Stars spread around the halo of large galaxies (like our own Milky Way and Andromeda) typically display old age, few elements other than hydrogen and helium, and move about the halo at high speeds. Their characteristics record the early dynamics and chemical evolution of the galaxy, including evidence of past collisions between two or more galaxies in the form of stellar streams – local enhancements in the density of stars that move as a coherent group through a galaxy.

Illustration of a galactic structure in the edge-on view. A stellar halo has a huge size with a diameter of over 500,000 light years and contains old halo stars and globular clusters.

Using data from Subaru’s Suprime Cam for photometry and Keck II’s Deep Extragalactic Imaging Multi-Object Spectrograph (DEIMOS) for spectroscopy to study the large spiral galaxy Andromeda, an international team of astronomers discovered two previously unseen streams by making detailed measurements of the halo stars' spatial and velocity distributions. The observations revealed the presence of red giant stars moving with a common velocity in distinct bands.

The team discovered the two new bands in the previously uncharted northern side of the galaxy's halo, located 200,000 and 300,000 light years away from the galactic centre, respectively. The study also confirmed previous observations of other streams, including a little-studied and very diffuse stream to the southwest.

False-colour map of the density of red giant stars in Andromeda, including the new streams E and F and a previously seen stream in the south west of the galaxy (SW), constructed from Subaru/Suprime-Cam images. The map extends out to a projected distance of 300,000 light years from Andromeda’s centre. Image: Mikito Tanaka (Tohoku University).

These streams are a result of mergers of dwarf galaxies associated with the formation of the stellar halo, and further study of the stars' chemical properties will provide more detailed information about their formation history. “Further observational surveys of an entire halo region in Andromeda will provide very useful information on galaxy formation, including how many and how massive individual dwarf galaxies as building blocks are and how star formation and chemical evolution proceeded in each dwarf galaxy,” says Mikito Tanaka of Tohoku University in Japan.

Since Andromeda shares similar characteristics with our own Milky Way Galaxy, understanding its evolutionary history will enable astronomers to learn more about the processes that defined the formation of our own Galaxy.

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.

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.

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!


© 2014 Pole Star Publications Ltd.