Galaxy collisions

Apr 09, 2013
A false-color, multi-wavelength image of the interacting galaxies M51A and M51B (The Whirlpool system). Blue corresponds to ultraviolet light from hot young stars, green to light from evolved stars, and red from warm dust heated by all stars. A new study of interacting galaxies analyzes their colors across this very broad spectral range. Credit: NASA/L.Lanz

Collisions between galaxies are common. Indeed, most galaxies have probably been involved in one or more encounters during their lifetimes. One example is our own Milky Way, which is bound by gravity to the Andromeda galaxy, our neighbor, and towards which we are approaching at a speed of about 50 kilometers per second, perhaps to meet in another billion years or so. Galaxy-galaxy interactions are thought to stimulate vigorous star formation because the encounters somehow induce the interstellar gas to condense into stars. These stimulated starbursts in turn light up the galaxies, especially at infrared wavelengths, making some systems hundreds or even thousands of times brighter than the Milky Way while they are active. Many of the massive stars that are produced become supernovae whose explosive deaths enrich the environment with carbon, oxygen, and all the other elements that are essential for life. Interacting galaxies are important not only in shedding light on how galaxies evolve, form stars, and seed the interstellar medium, but because they can be very bright and seen across cosmological distances.

The details of are only approximately understood, in part because most observed interactions involve galaxies of unequal sizes, morphologies, and stages of the interaction. Since an interaction takes billions of years to run its course, it is not possible to watch an entire sequence of events. Scientists trying to figure out the evolution of a collision can only observe many different systems at different stages, and then try to correct for all the other factors (like mass or shape) that might influence the analysis. New space-based telescopes offer some help because they can collectively observe at all wavelengths from the ultraviolet to far . These wavelengths capture most of the global activity present in galaxies from star formation: The UV detects the hottest and youngest , the far infrared senses dust warmed by otherwise obscured stellar radiation, while the intermediate wavelengths sample a range of other contributing phenomena.

CfA astronomers Lauranne Lanz, Andreas Zezas, Howard Smith, Matt Ashby, Giovanni Fazio, Lars Hernquist, and Patrik Jonsson have used new observations of thirty-one in fourteen systems to publish the first systematic analysis of the energy distribution of interacting galaxies across this key, broad spectral range. The galaxies are from a sample that includes all stages of interaction, from early stages when disruption has only just began to near final stages when the effects of the collision are prominent; the published set contain every interacting galaxy in the sample for which the full dataset was available.

The team measured - and then modeled - these objects at twenty-five different wavelength bands in an effort to test how star formation and related galaxy properties are influenced in an interaction. They report that the radiative output of the dust, and its temperature, increase as the interaction progresses, and provide evidence that the star formation rate does increase as the interaction progresses. But somewhat surprisingly, they find after taking into account the different galaxy masses that the rate enhancements are not as dramatic as had been expected. This perhaps reflects the limited size of the current sample and/or the fact that because induced bursts of star formation are confined to short time intervals, they just happen to be under-represented in the current sample. The astronomers conclude by outlining future analyses that incorporate the results of simulations of interacting galaxies in order to fill in some of the missing details.

Explore further: Astronomers see pebbles poised to make planets

Related Stories

Twists and turns in interacting galaxies

Oct 08, 2012

(—Almost thirty years ago the Infrared Astronomy Satellite, IRAS, discovered that the universe contained many fabulously luminous galaxies, some of them more than a thousand times brighter than ...

Spitzer photo atlas of galaxy 'train wrecks'

May 25, 2011

( -- Five billion years from now, our Milky Way Galaxy will collide with the Andromeda Galaxy. This will mark a moment of both destruction and creation. The galaxies will lose their separate identities ...

Hubble catches the moment the lights went out

Feb 06, 2013

(—The further away you look, the further back in time you see. Astronomers use this fact to study the evolution of the Universe by looking at nearby and more distant galaxies and comparing their ...

Black holes and star formation

Feb 09, 2012

( -- It has long been recognized that galaxy mergers or even close interactions can play a vital role in shaping the morphology of galaxies. One way they can do so, it is thought, is by triggering ...

Antennae Galaxies

May 19, 2008

This image of the Antennae galaxies is the sharpest yet of this merging pair of galaxies. During the course of the collision, billions of stars will be formed. The brightest and most compact of these star ...

Building galaxies

Jul 11, 2011

( -- Galaxies frequently collide with one another. Our own Milky Way galaxy, for example, and its nearest giant neighbor, the Andromeda galaxy, are heading towards each other at a rate of about ...

Recommended for you

Astronomers see pebbles poised to make planets

5 hours ago

A team of astronomers led from St Andrews and Manchester universities today (6 July) announced the discovery of a ring of rocks circling a very young star. This is the first time these 'pebbles', thought ...

Small cosmic 'fish' points to big haul for SKA Pathfinder

6 hours ago

A wisp of cosmic radio waves, emitted before our solar system was born, shows that a new radio telescope will be able to detect galaxies other telescopes can't. The work, led by Dr James Allison of the Commonwealth ...

Gaia produces stellar density map of the Milky Way

6 hours ago

This image, based on housekeeping data from ESA's Gaia satellite, is no ordinary depiction of the heavens. While the image portrays the outline of our Galaxy, the Milky Way, and of its neighbouring Magellanic ...

Hubble view: Wolf-Rayet stars, intense and short-lived

Jul 03, 2015

This NASA/European Space Agency (ESA) Hubble Space Telescope picture shows a galaxy named SBS 1415+437 (also called SDSS CGB 12067.1), located about 45 million light-years from Earth. SBS 1415+437 is a Wolf-Rayet ...

NASA image: Stellar sparklers that last

Jul 03, 2015

While fireworks only last a short time here on Earth, a bundle of cosmic sparklers in a nearby cluster of stars will be going off for a very long time. NGC 1333 is a star cluster populated with many young ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (1) Apr 10, 2013
The galaxies collisions, is theoretically impossible if there it isn't happened something unexpectedly. The galaxies create they own fields through inter-movement between them, see USM So the galaxies draw near and remove, but never collided!

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.