Growing galaxies gently

Oct 13, 2010
This artist's impression shows a young galaxy, about two billion years after the Big Bang, accreting material from the surrounding hydrogen and helium gas and forming many young stars. New results from ESO's Very Large Telescope have provided the first direct evidence that the accretion of pristine gas alone, without the need for violent major mergers, can fuel vigorous star formation and the growth of massive galaxies in the young universe. Credit: ESO/L. Calçada

The first galaxies formed before the Universe was less than one billion years old and were much smaller than the giant systems -- including the Milky Way -- that we see today. So somehow the average galaxy size has increased as the Universe has evolved. Galaxies often collide and then merge to form larger systems and this process is certainly an important growth mechanism. However, an additional, gentler way has been proposed.

A European team of astronomers has used ESO's Very Large to test this very different idea — that young can also grow by sucking in cool streams of the hydrogen and helium gas that filled the early Universe and forming new stars from this primitive material. Just as a commercial company can expand either by merging with other companies, or by hiring more staff, young galaxies could perhaps also grow in two different ways — by merging with other galaxies or by accreting material.

The team leader, Giovanni Cresci (Osservatorio Astrofisico di Arcetri) says: "The new results from the VLT are the first direct evidence that the accretion of pristine gas really happened and was enough to fuel vigorous star formation and the growth of massive galaxies in the young Universe." The discovery will have a major impact on our understanding of the evolution of the Universe from the Big Bang to the present day. Theories of galaxy formation and evolution may have to be re-written.

The group began by selecting three very distant galaxies to see if they could find evidence of the flow of pristine gas from the surrounding space and the associated formation of new stars. They were very careful to make sure that their specimen galaxies had not been disturbed by interactions with other galaxies. The selected galaxies were very regular, smoothly rotating discs, similar to the , and they were seen about two billion years after the Big Bang (at a redshift of around three).

In galaxies in the modern Universe the heavy elements [1] are more abundant close to the centre. But when Cresci's team mapped their selected distant galaxies with the SINFONI spectrograph on the VLT [2] they were excited to see that in all three cases there was a patch of the galaxy, close to the centre, with fewer heavy elements, but hosting vigorously forming stars, suggesting that the material to fuel the star formation was coming from the surrounding pristine gas that is low in heavy elements. This was the smoking gun that provided the best evidence yet of young galaxies accreting primitive gas and using it to form new generations of stars.

As Cresci concludes: "This study has only been possible because of the outstanding performance of the SINFONI instrument on the VLT. It has opened a new window for studying the chemical properties of very distant galaxies. SINFONI provides information not only in two spatial dimensions, but also in a third, spectral dimension, which allows us to see the internal motions inside galaxies and study the chemical composition of the interstellar gas."

Notes:

[1] The gas filling the early was almost all hydrogen and helium. The first generations of stars processed this primitive material to create heavier elements such as oxygen, nitrogen and carbon by nuclear fusion. When this material was subsequently spewed back into space by intense particle winds from massive young stars and supernova explosions the amounts of heavy elements in the galaxy gradually increased. Astronomers refer to elements other than hydrogen and helium as "heavy elements".

[2] By carefully splitting up the faint light coming from a galaxy into its component colours using powerful telescopes and spectrographs, astronomers can identify the fingerprints of different chemicals in remote galaxies, and measure the amounts of heavy elements present. With the SINFONI instrument on the VLT astronomers can go one better and get a separate spectrum for each part of an object. This allows them to make a map that shows the quantity of heavy elements present in different parts of a galaxy and also determine where in the galaxy is occurring most vigorously.

Explore further: Astronomer confirms a new "Super-Earth" planet

More information: This research was presented in a paper, Gas accretion in distant galaxies as the origin of chemical abundance gradients, by Cresci et al., to appear in Nature on 14 October 2010.

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User comments : 10

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omatumr
1.8 / 5 (10) Oct 13, 2010
Yes, galaxies grew from the compact object that is still visible at the galactic center.

Why? Because the cosmos is fragmenting and expanding.

Why? Because nuclear matter is fragmenting and expanding.

Why? Neutron repulsion.

This is explained here:

www.youtube.com/w...e_Qk-q7M

With kind regards,
Oliver K. Manuel
Former NASA Principal
Investigator for Apollo
kevinrtrs
1 / 5 (8) Oct 14, 2010
accreting material from the surrounding hydrogen and helium gas and forming many young stars


Ahhhh....our dear friend the accreting wunder-thing.

Unfortunately not enough time has passed for galaxies to have formed by this method. There are not enough type III supernovas recorded for this to have occurred by this particular method.
Please let me know just how many and where type III supernovas have been sighted.
Even in our own solar system, the gas giants couldn't have formed by this method according to this accreting-dust-eating-wonder recipe of planet formation, at least not in the universe's lifetime.

_ilbud
4.2 / 5 (5) Oct 14, 2010
Kevin you believe in magic tricks like jebus and magic floods so maybe your magic voodoo god did it. Please provide signed photographic evidence.
Skeptic_Heretic
3.7 / 5 (7) Oct 14, 2010
Unfortunately not enough time has passed for galaxies to have formed by this method. There are not enough type III supernovas recorded for this to have occurred by this particular method.
Produce your calculations. In the early Universe stars would have been far more massive on average than they are today. A star like our sun would be an unheard of rarity. Type 3 supernovae would be the norm, not the exception.
Even in our own solar system, the gas giants couldn't have formed by this method according to this accreting-dust-eating-wonder recipe of planet formation, at least not in the universe's lifetime.
Well this is demonstrably false as predicted utilizing the simple math provided by Newton. Are you really that far out of date?

Oh yes, I forgot, you're still working your way through the knowledge of the first century. Derivative calculus is another 1500 years in the making for you. Let us know when you catch up.
Donutz
4.5 / 5 (8) Oct 14, 2010
This is great! Omatumr and kevinrts duking it out in the same thread for the looney tune title! Go for it, boys. See who can out-psycho the other without either one ever presenting a shred of evidence.

Oh, the entertainment value!
yyz
5 / 5 (7) Oct 14, 2010
"There are not enough type III supernovas recorded for this to have occurred by this particular method."

"Please let me know just how many and where type III supernovas have been sighted"

Kev, you're making stuff up again. What is a type III SN? Did you read about them in your Big Science Book? I can't find anything about type III SN in contemporary astronomy texts. Were you referring to Population III stars?

Read carefully and you will see they are talking about accretion of pristine, low-z(metallicity) gas onto pre-existing galaxies. This is just another process (like galaxy collisions) that can come in to play in the growth of galaxies. No one is claiming (besides you) that whole galaxies form by accretion alone (you need something for the gas to accrete onto, no?).

@Donutz, LOL. Agreed, a little crank on crank action would liven things up a bit. :^)
Skeptic_Heretic
5 / 5 (1) Oct 14, 2010
@yyz, I was surprised that Kev knew what a tpye 3 was.
http://www.site.u...upernova
It's a theoretical construct now called by another name. It's a core collapse typified by the explosive shedding of all hydrogen and helium layers.
It shows how old the textbooks he references are.
yyz
5 / 5 (2) Oct 14, 2010
@SH,

"I was surprised that Kev knew what a tpye 3 was. "

I don't think he did...that's why I asked. Given his poor knowledge of most of science, I'd like to hear his explanation. Given that this is an obscure, obsolete term mentioned rarely in the literature(likely used by godless, athiestic astronomers in the 60's and 70's), I highly doubt kev was referring to supernovae.

So, what is it, kev?

[BTW, if you google Type III supernovae, a highly ranked 1991 paper by Langer on SN 1987A is mistakenly listed. There is no mention of this term in the paper: http://articles.a...ype=.pdf ]
yyz
not rated yet Oct 14, 2010
Meant to add: I don't see any direct connection between supernovae and this discovery to begin with.
Tuxford
1 / 5 (3) Nov 15, 2010
This is direct evidence that explosive outbursts from the galactic center injected new material for star formation, not for solely accreting material from pre-existing gas clouds. See LaViolette.

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