Wednesday, December 7, 2016

Young galaxies "born" at least 50 stars annually

photo: nasa.gov



Young galaxies in the universe appear to be very fertile and, with an annual average of 50 new stars on the size of the sun.

The recent discovery shows as "incubators" within young galaxies annually produce more stars than was originally estimated. Astronomers have "traveled" back 12.5 billion years to study one of the most remote galaxies known MS1358arc. Light began its journey in the universe just one billion years after the creation of the cosmos, from the Big Bang.

The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby galaxies.


Galaxy formation is hypothesized to occur, from structure formation theories, as a result of tiny quantum fluctuations in the aftermath of the Big Bang. The simplest model for this that is in general agreement with observed phenomena is the Λ-Cold Dark Matter cosmology; that is to say that clustering and merging is how galaxies gain in mass, and can also determine their shape and structure.

Commonly observed properties of galaxies


Because of the inability to conduct experiments in outer space, the only way to “test” theories and models of galaxy evolution is to compare them with observations. Explanations for how galaxies formed and evolved must be able to predict the observed properties and types of galaxies.

Edwin Hubble created the first galaxy classification scheme known as the Hubble tuning-fork diagram. It partitioned galaxies into ellipticals, normal spirals, barred spirals (such as the Milky Way), and irregulars. These galaxy types exhibit the following properties which can be explained by current galaxy evolution theories:
Hubble tuning fork diagram of galaxy morphology photo: wikipedia.org

Many of the properties of galaxies (including the galaxy color–magnitude diagram) indicate that there are fundamentally two types of galaxies. These groups divide into blue star-forming galaxies that are more like spiral types, and red non-star forming galaxies that are more like elliptical galaxies.

Spiral galaxies are quite thin, dense, and rotate relatively fast, while the stars in elliptical galaxies have randomly-oriented orbits.
The majority of mass in galaxies is made up of dark matter, a substance which is not directly observable, and might not interact through any means except gravity.

The majority of giant galaxies contain a supermassive black hole in their centers, ranging in mass from millions to billions of times the mass of our Sun. The black hole mass is tied to the host galaxy bulge or spheroid mass.

Metallicity has a positive correlation with the absolute magnitude (luminosity) of a galaxy.


Hubble thought incorrectly that the tuning fork diagram described an evolutionary sequence for galaxies, from elliptical galaxies through lenticulars to spiral galaxies. However, astronomers now believe that disk galaxies likely formed first, then evolved into elliptical galaxies through galaxy mergers.

So-called "gravitational lenses" were used to enlarge the galaxy using light how "fits" on a nearby star cluster. With this technique, the researchers could observe rapid ascent generated by the formation of new stars. Thus, they could conclude that new stars are created in the galaxy at a speed 100 times higher than the average forecast initially.

With a diameter of 6000 light-years, "collection" of stars will most likely evolve into a new spiral galaxy similar to the Milky Way.
Artist image of a firestorm of star birth deep inside core of young, growing elliptical galaxy. photo: wikipedia.org
Galaxy mergers and the formation of elliptical galaxies 

Elliptical galaxies (such as IC 1101) are among some of the largest known thus far. Their stars are on orbits that are randomly oriented within the galaxy (i.e. they are not rotating like disk galaxies). A distinguishing feature of elliptical galaxies is that the velocity of the stars does not necessarily contribute to flattening of the galaxy, such as in spiral galaxies. Elliptical galaxies have supermassive black holes at their center, and the mass of these black holes correlates with the galaxy’s mass.
NGC 4676 (Mice Galaxies) is an example of a present merger. photo: wikipedia.org

Elliptical galaxies have two main stages of evolution. The first is due to the supermassive black hole increasing in size from accreting cooling gas. The second stage is marked by the black hole stabilizing by suppressing gas cooling, thus leaving the elliptical galaxy in a stable state.The mass of the black hole is also correlated to a property called sigma which is the dispersion of the velocities of stars in the elliptical galaxies. 

This relationship, known as the M-sigma relation, was discovered in 2000. Elliptical galaxies do not have disks around them, although some bulges of disk galaxies look similar to elliptical galaxies. It is more likely to find elliptical galaxies in more crowded regions of the universe (such as galaxy clusters).
Antennae Galaxies are a pair of colliding galaxies - the bright, blue knots are young stars that have recently ignited as a result of the merger. photo: wikipedia.org


Astronomers now see elliptical galaxies as some of the most evolved systems in the universe. It is widely accepted that the main driving force for the evolution of elliptical galaxies is mergers of smaller galaxies. Many galaxies in the universe are gravitationally bound to other galaxies, which means that they will never escape the pull of the other galaxy. 
ESO 325-G004, a typical elliptical galaxy. photo: wikipedia.org

If the galaxies are of similar size, the resultant galaxy will appear similar to neither of the two galaxies merging,but will instead be an elliptical galaxy. There are many types of galaxy mergers, which do not necessarily result in elliptical galaxies, but result in a change in the structure of the mergers. For example, a minor merger event is thought to be occurring between the Milky Way and the Magellanic Clouds.



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The above post is reprinted from materials provided by The Telegraph and Wikipedia . Note: Materials may be edited for content and length.

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