A massive galaxy long ago and far away

A massive galaxy long ago and far away
An extremely massive elliptical galaxy at about three billion years after the big bang, as seen in an optical/near-infrared image. The galaxy is about ten times more massive than the Milky Way. Today the galaxy is not actively producing new stars, but its population of old, red stars appears to be the result of earlier episodes during which the galaxy was one of the most active star-forming examples known. Credit: NASA/Hubble

Galaxies today fall roughly into two categories: elliptically-shaped collections of reddish, old stars that formed predominantly during a period early in the history of the universe, and spiral shaped objects dominated by blue, young stars. The Milky Way is an example of the latter, a spiral galaxy actively making new stars. In order to understand the growth of galaxies over cosmic time and the past star formation history of the universe, astronomers study the population of old stars in distant ellipticals from earlier epochs, stars which in turn formed at an even early time. Star formation produces supernovae which enrich their environments with elements, including the diagnostic element magnesium. Measuring the amount of magnesium (relative to iron) in a galaxy thus helps to fix the strength and duration of prior episodes of star formation.

CfA astronomers Charlie Conroy and Jieun Choi and eight colleagues used the spectrometer on the Keck telescope (along with some secondary datasets) to obtain very sensitive magnesium measurements in one of the most massive and luminous elliptical known. The galaxy, seen at an epoch only three billion years after the big bang, has a stellar mass of about three hundred billion solar-masses (the Milky Way's stellar mass is about ten times less) but is currently making at a rate only about half that of the Milky Way. However, it's magnesium-to-iron ratio indicates that earlier in its life it was making stars at a phenomenally high rate, perhaps as many as several thousand solar-masses each year, making it one of the most vigorous examples of star-formation known.

The scientists conclude that the bursts of in this galaxy must have been due to mergers with other galaxies. In fact, they estimate that the object probably doubled in sized as a consequence of accreting smaller galaxies. Unfortunately this particular elliptical is so unusual that it cannot be considered a typical progenitor for any local elliptical galaxy. The team argues that additional observations of more, less extreme ellipticals in the early universe are now needed to fill in the rest of the story. The instruments on the James Webb Space Telescope, to be launched next year, should be capable of doing so.


Explore further

Image: Hubble's compact blue dwarf galaxy UGC 11411

More information: Mariska Kriek et al. A massive, quiescent, population II galaxy at a redshift of 2.1, Nature (2016). DOI: 10.1038/nature20570
Journal information: Nature

Citation: A massive galaxy long ago and far away (2017, February 6) retrieved 21 May 2019 from https://phys.org/news/2017-02-massive-galaxy.html
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RNP
Feb 06, 2017
Open access copy of the Nature article here: https://arxiv.org...2001.pdf

Feb 06, 2017
but is currently making stars at a rate only about half that of the Milky Way

based on certain unverifiable assumptions since no one has so far witnessed and recorded ANY star birth. This therefore makes this statement and in fact the rest of the conclusions based on it a whole lot of non-science.

Feb 06, 2017
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Feb 06, 2017
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Feb 06, 2017
The red color (the red shift) is directly related to the distance traveled of the waves.
 
"Greater distance weakens the intensity (force) of waves (radiation). Lesser intensity of waves is registered as a greater shift into order." from http://www.svemir...f-colors
"Observing the Universe through colors"

Feb 06, 2017
"The galaxy, seen at an epoch only three billion years after the big bang, has a stellar mass of about three hundred billion solar-masses (the Milky Way's stellar mass is about ten times less) ..."

Current estimates place the Milky Way's stellar mass at anywhere from 700 billion solar masses (http://www.scienc...-answer) to 1.5 trillion solar masses (https://en.wikipe...ky_Way), not 30 billion.

Shabby.


Feb 08, 2017
I am wondering how they know that the galaxy is "today" producing fewer stars? Considering at 3 B years after the BB, it would be now some 11 B Light Years away from us, and more with expansion, so we would have to wait taht long for the light from whatever the galaxy has turned into in that 11 B years of it's formation, til now, that we have not yet seen.

Yes, it is a niggling point, but needs to be made. I understand taht the galaxy is producing fewer stars as we SEE it Now, but that is not the same as what the galaxy is Actually Doing right now.

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