Astronomers peer into the dark

Apr 21, 2011
An image of a galaxy cluster discovered in the GAMA group catalogue. This is a inverse colour composite of ultraviolet, visible light and infrared images so redder galaxies appear blue and vice-versa. Galaxies in the cluster are highlighted with circles, with the size of the circle proportional to the mass of the galaxy. The colour of the circle indicates the true colour of the galaxy. In this image a mixture of galaxy types are visible, but very few blue (star-forming) galaxies. The brightest galaxy is located at the centre. Credit: GAMA / Aaron Robotham.

(PhysOrg.com) -- Astronomers from the Scottish Universities Physics Alliance (SUPA) have produced a completely new catalogue of ~15,000 groups of galaxies that gives a new insight into dark matter, the material of unknown composition that makes up a fifth of the mass of the Universe. Dr. Aaron Robotham of the University of St Andrews will present the work of the Galaxy and Mass Assembly (GAMA) team in his talk on Thursday 21 April at the Royal Astronomical Society's National Astronomy Meeting in Llandudno, Wales.

Current models of the Universe predict that reside in large clumps of , commonly referred to as dark matter halos. Unlike individual galaxies, galaxy groups provide a unique environment in which to study the properties of this elusive material. Understanding the 20% of the cosmos comprised of dark matter is important – in comparison only 3% of the mass of Universe consists of 'ordinary' matter.

"The motions of the galaxies inside the groups provide a direct method for studying the properties of dark matter", says Dr Aaron Robotham who leads the group catalogue project. "Studying dark matter in galaxies is confused by normal processes such as star formation, while this unseen material dominates the motions of galaxies in groups."

Dr. Robotham describes the construction of the group catalogue, which is a significant improvement on previous similar attempts with much shallower surveys. "The sample has some of the most massive bound structures ever measured. These range from the equivalent of a million billion times the mass of the Sun down to a mere few thousand billion solar masses. To have this range of dark matter halo masses within a single study is unprecedented."

The segments show 12-degree wide maps of the positions of the galaxies in the GAMA catalogue. The Earth is at the bottom of each wedge, with the most distant galaxies at the top (at a distance of 6000 lightyears). Circles indicate groups included in the catalogue, where larger circles show groups with more members. Credit GAMA / Aaron Robotham.

"Some of our groups contain hundreds of galaxies while others only a handful", says Dr. Peder Norberg, a co-investigator based at the Royal Observatory Edinburgh, "the ratio of the number of very high mass to very low mass groups is a direct indicator of the type of dark matter that the Universe contains. Hot or warm dark matter (meaning light particles) suppresses the formation of low mass halos while cold dark matter (heavy particles) encourages their formation."

It will take a further few years of detailed studies, with a large range of models, before a definite conclusion can be reached on whether the new GAMA data and supercomputer predictions (based on the popular Cold Dark Matter model of the ) are in good agreement or not.

"Currently the differences seen between the model and the data can be understood as limitations in the galaxy formation model used, explaining why intense modelling and further studies are required, and hopefully leading to some exciting new findings in the years ahead with possibly the first new insight into the properties of dark matter particles," adds Dr. Norberg.

GAMA team leader Professor Simon Driver of the University of St Andrews and the International Centre for Radio Astronomy Research at the University of Western Australia, says this group catalogue is the first big step of 4 years of data gathering by the GAMA Team at the Anglo-Australian Telescope. "The catalogue will provide the opportunity to study how gravity works over an unprecedented mass range and using data from other telescopes around the world we will shed fresh light on how dark mater helps to turn gas into stars".

Explore further: Gas cloud in the galactic centre is part of a larger gas streamer

Related Stories

Cosmologists 'see' the cosmic dawn

Feb 11, 2009

(PhysOrg.com) -- The images, produced by scientists at Durham University's Institute for Computational Cosmology, show the "Cosmic Dawn" - the formation of the first big galaxies in the Universe.

Does the sun hold a dark secret?

Jul 21, 2010

(PhysOrg.com) -- A scientist at Royal Holloway, University of London believes dark matter is lurking at the centre of the sun and cooling down its core temperature.

Recommended for you

Image: Hubble captures the Egg Nebula

3 hours ago

This colourful image shows a cosmic lighthouse known as the Egg Nebula, which lies around 3000 light-years from Earth. The image, taken with the NASA/ESA Hubble Space Telescope, has captured a brief but dramatic ...

'Blockbuster' science images

Nov 21, 2014

At this point, the blockbuster movie Interstellar has created such a stir that one would almost have to be inside a black hole not to know about it. And while the science fiction thriller may have taken some ...

Estimating the magnetic field of an exoplanet

Nov 20, 2014

Scientists developed a new method which allows to estimate the magnetic field of a distant exoplanet, i.e., a planet, which is located outside the Solar system and orbits a different star. Moreover, they ...

It's filamentary: How galaxies evolve in the cosmic web

Nov 20, 2014

How do galaxies like our Milky Way form, and just how do they evolve? Are galaxies affected by their surrounding environment? An international team of researchers, led by astronomers at the University of ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

eachus
5 / 5 (1) Apr 21, 2011
Distance in millions of lightyears, putting six billion light years at the top of the charts...
Moebius
2.5 / 5 (2) Apr 21, 2011
Flashback newsreel headline AD1543:
New research into the antigravity antimatter (AA matter) that surrounds the solar system and keeps the planets and sun circling our earth reveals that it must permeate the entire universe. Not only is the earth the center of our solar system but it must also be the center of the universe too. The only solution to this is the so far undetected AA matter. There are several new theories as to what this mysterious substance must be and scientists the world over are devising experiments to determine exactly what it is.

On a side note scientist Nicolaus 'the mad' Copernicus published his discredited theory that the sun is actually the center of the solar system, neither it or the earth are the center of universe and AA matter isn't required and doesn't exist. This book is not expected to make the best seller list or go into a second printing.
El_Nose
not rated yet Apr 22, 2011
a fifth of the mass ???

how does that compare with 90%+ of all baryoinic matter??

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.