Galaxies the way they were

Apr 03, 2013
A Hubble image of a field of distant galaxies. The CANDELS project has analyzed these and other data to study how galaxies form and evolve in the early universe. Credit: NASA/Hubble

(Phys.org) —Galaxies today come very roughly in two types: reddish, elliptically shaped collections of older stars, and bluer, spiral shaped objects dominated by young stars. The conventional wisdom is that the two types are related to one another, ellipticals representing an older, more evolved stage of galaxies. Astronomers have discovered during the past decade that these two categories seem also to apply to galaxies in the early universe. In particular, galaxies so distant from us that their light has been traveling for about eleven and one-half billion years, 84% of the age of the universe, also generally fall into these two groups.

A major puzzle about these early galaxy types involves their specific properties: Red today are generally large in diameter, but in the distant cosmos the corresponding galaxies are much smaller - perhaps five times smaller than local ones of the same mass and much smaller than their blue, star-forming colleagues. If galaxies gain in mass with time, through collisions or other processes, they would be expected also to increase in size with time. Therefore, if the early red galaxies really do represent older stages of bluer objects, then as a class they should be more massive and larger, not smaller.

The CANDELS project (Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey) has acquired a very large database of optical and of distant galaxies. Writing in one of their new papers this month, CfA astronomer Matt Ashby and the CANDELS team propose a solution to the dilemma. They studied a set of galaxies whose light has been en route for between about nine and twelve billion years. Based on the measured rates of star formation in blue galaxies inferred from the radiation, they conclude that they have undergone collisions that induce star formation. That's what makes them shine exceptionally brightly. After a billion years or so, however, these starbursts leave many of them depleted in fuel, and as a result the galaxies shrink in size to become the compact red galaxies that are so puzzling. In the later universe star-forming galaxies have grown to considerably larger sizes, and their star formation is consequently spread across much larger volumes, so that the same quenching mechanism does not take place, leaving them to retain their sizes as ellipticals.

Explore further: NASA missions monitor a waking black hole

Related Stories

Hubble catches the moment the lights went out

Feb 06, 2013

(Phys.org)—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 ...

Radio galaxies in the distant universe

Jun 26, 2012

(Phys.org) -- For over a decade astronomers have been probing a region of the northern sky, not far from the handle of the Big Dipper, that is relatively free of bright stars and the diffuse glow of the Milky ...

Mysterious red galaxies

Dec 12, 2011

(PhysOrg.com) -- Perhaps the most astonishing and revolutionary discovery in cosmology was Edwin Hubble's observation that galaxies are moving away from us with velocities that are proportional to their distances. ...

Galaxies in the young cosmos

May 21, 2012

(Phys.org) -- The universe was born about 13.7 billion years ago in the big bang. The Sun and its system of planets formed about five billion years ago. What happened, then, during that long, intervening stretch ...

Making stars in early galaxies

Dec 10, 2012

(Phys.org)—Ten billion years ago or so, at least according to the current picture, the youthful universe began to produce an abundance of new stars. The very first ones appeared in the young cosmos after ...

How can growing galaxies stay silent?

Dec 19, 2011

Beginning around 2005, astronomers began discovering the presence of very large galaxies at a distance of around 10 billion lightyears. But while these galaxies were large, they didn’t appear to have ...

Recommended for you

NASA missions monitor a waking black hole

7 hours ago

NASA's Swift satellite detected a rising tide of high-energy X-rays from the constellation Cygnus on June 15, just before 2:32 p.m. EDT. About 10 minutes later, the Japanese experiment on the International ...

What is the habitable zone?

17 hours ago

The weather in your hometown is downright uninhabitable. There's scorching heatwaves, annual tyhpoonic deluges, and snow deep enough to bury a corn silo.

Galaxy survey to probe why the universe is accelerating

18 hours ago

We know that our universe is expanding at an accelerating rate, but what causes this growth remains a mystery. The most likely explanation is that a strange force dubbed "dark energy" is driving it. Now a ...

High resolution far-infrared all-sky image data release

19 hours ago

A research group led by a University of Tokyo researcher, using the AKARI satellite's Far-Infrared All-Sky data, have created all-sky image maps and released the full database to researchers around the world ...

User comments : 0

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.