Shedding light on galaxy rotation secrets

July 14, 2017
Spiral galaxies are found to be strongly rotating, with an angular momentum higher by a factor of about 5 than ellipticals. What is the origin of such a difference? Credit: Wikimedia Common

The dichotomy concerns the so-called angular momentum (per unit mass) that in physics is a measure of size and rotation velocity. Spiral galaxies are found to be strongly rotating, with an angular momentum higher by a factor of about five than ellipticals. What is the origin of such a difference? An international research team investigated the issue in a study just published in the Astrophysical Journal. The team was led by SISSA Ph.D. student JingJing Shi under the supervision of Prof. Andrea Lapi and Luigi Danese, and in collaboration with Prof. Huiyuan Wang from USTC (Hefei) and Dr. Claudia Mancuso from IRA-INAF (Bologna). The researchers inferred from observations the amount of gas fallen into the central region of a developing galaxy, where most of the star formation takes places.

The outcome is that in elliptical galaxies, only about 40 percent of the available gas fell into that central region. More relevantly, this gas fueling star formation was characterized by a rather low . This is in stark contrast with the conditions found in spirals, where most of the gas that ends up in stars has an appreciably higher angular momentum. The researchers have traced the dichotomy in the angular momentum of spiral and elliptical galaxies to their different formation histories. Elliptical galaxies form most of their stars in a fast collapse in which angular momentum is dissipated. This process is likely stopped early on by powerful gas outflows from supernova explosions, stellar winds and possibly even from the central supermassive black hole. For spirals, on the other hand, the gas fell slowly, conserving its angular momentum, and stars formed steadily along a timescale comparable to the age of the universe.

"Until recent years, in the paradigm of and evolution, were thought to have formed by the merging of stellar disks in the distant universe. Along this line, their angular momentum was thought to be the result of dissipative processes during such merging events," the researchers write. Recently, this paradigm had been challenged by far-infrared/sub-millimeter observations brought about by the advent of space observatories like Herschel and ground-based interferometers like the Atacama Large Millimeter Array (ALMA).

These observations have the power of penetrating through interstellar dust thus unveiling the star formation processes in the very distant, dusty galaxies that constituted the progenitors of local ellipticals. "The net outcome from these observations is that the populating present-day ellipticals are mainly formed in a fast dissipative collapse in the central regions of dusty star-forming . After a short timescale of less than 1 billion years, the has been quenched by powerful gas outflows." Despite this change of perspective, the origin of the low angular momentum observed in local ellipticals remained unclear.

"This study reconciles the low angular momentum observed in present-day ellipticals with the new paradigm emerging from Herschel and ALMA observations of their progenitors," conclude the scientists. "We demonstrated that the low angular of ellipticals is mainly originated by nature in the central regions during the early galaxy formation process, and not nurtured substantially by the environment via merging events, as envisaged in previous theories."

Explore further: The shapes of galaxies

More information: J. Shi et al. Angular Momentum of Early- and Late-type Galaxies: Nature or Nurture?, The Astrophysical Journal (2017). DOI: 10.3847/1538-4357/aa7893

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5 / 5 (4) Jul 14, 2017
An open access copy of the paper can be found here;
5 / 5 (2) Jul 14, 2017
@RNP: Question on angular momentum:
Since this is a conserved quality do you have an idea how much the central black hole skews the *observed* angular momentum of a galaxy? Particularly with the first galaxies the angular momentum of its mass should be a wide distribution around x (where x is the average, local angular momentum for a relevant region for the formation of this galaxy). The stuff with near zero angular momentum should eventually sink to the center ofthe galaxy and be captured by the black hole. I.e. while not removed from the angular momentum sum it is removed from observation, so that we only continue to see stuff that is skewed towards higher angular momentum?
Jul 14, 2017
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1 / 5 (1) Jul 14, 2017
A well-known basic process in the universe. Rotation + gravity.

For galaxies it is the same as for planets and stars, always (99.9%) the faster rotation of the central body than the body in orbit. The speed of rotation, the center of the galaxy, determines the appearance of the galaxy. speed cyclone, from the north pole to the south pole center of the galaxy, given the speed of the central body of the galaxy. Speed cyclone from pole to pole center of the galaxy, given the speed of the central body of the galaxy.
"The number of satellites orbiting around a planet is directly related to the mass of a planet and its rotation around its axis."
not rated yet Jul 14, 2017
Does this add another twist to the puzzle of spiral galaxies' rotation rate ? Does it mean an elliptical's hypothesised primordial 'Dark Matter' has mostly fallen into core to feed the mega-BH ?? Compared to a spiral's distribution, that is ?
1 / 5 (2) Jul 14, 2017
If you close your eyes you will find you are in a black hole.
Da Schneib
3 / 5 (4) Jul 14, 2017
Very interesting. There should be a lot of simulations altered by this finding, and galaxy mergers may have to be at least partially re-thought in light of this new information. We're already seeing the effects of infrared and lower frequency observations in this and other areas; I can't wait to see what we find out when the JWST is up and online.
3 / 5 (4) Jul 14, 2017
Most importantly of all, this will require @Bunni to reformulate all his claims with regard to the theorized influence of DM on the rotational velocities of spiral vs elliptical galaxies.

It will be interesting to see the contortions necessary to adapt these new findings to his idee fixe.
Jul 15, 2017
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Jul 15, 2017
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Jul 16, 2017
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Jul 16, 2017
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Jul 16, 2017
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not rated yet Jul 17, 2017
DB, I find your perception of the Galaxies as 'Hyper-dimensional' as an interesting speculation.

I just wonder how long it will take to accumulate observable and repeatable evidence to support or contradict that hypothesis, in part or whole.

Relying on computer simulations as 'proof' always leaves me wondering... If those simulations are an expression of reality or human imagination?
Jul 17, 2017
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Jul 17, 2017
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