JAXA: Chemical Composition of Universe Is Similar on Large & Small Scales

[bystander]

Suzaku satellite reveals the average chemical composition of our
Universe on the largest scales to be the same as that of our Sun
Japan Aerospace Exploration Agency (JAXA) | 2015 Oct 20

All of the chemical elements that are heavier than carbon, the oxygen we breathe, the silicon that makes up the sand on the beach, were produced inside stars through nuclear fusion and released by stellar explosions called supernovae. By measuring the chemical composition of the Universe, scientists are trying to reconstruct the history of how, when, and where each of the chemical elements so necessary for the evolution of life were produced.

Very generally speaking, there are two ways that a supernova explosion can take place, and the proportion of chemical elements that are produced depend on the supernova type. Lighter elements, like oxygen and magnesium, originate mainly from the explosions of very massive stars, more than 10 times the size of our Sun, at the end of their lifetimes. These are known as “core-collapse supernovae”. Smaller stars instead usually end their life cycles as “white dwarves”, a small fraction of which can explode as a “thermonuclear” or “type Ia” supernova if they later accrete matter from a companion star, causing the white dwarf to become unstable to the pull of its own gravity. Heavier atoms like iron and nickel mostly come from this latter type of supernovae. To make up the chemical composition of our Solar System, for instance, we require a mixture of roughly one thermonuclear for every five core-collapse supernova explosions. JAXA research fellow Aurora Simionescu wanted to find out whether the average chemical composition of the Universe was similar to that of our Solar System, or whether our local neighborhood was, after all, a special place.

Actually, perhaps counterintuitively, the answer to this question is best found not by looking at the stars themselves, but rather looking at the intergalactic space. That is because most of the normal matter in the universe, and thus also most of the metals, are presently not contained in stars, but rather in a very hot, diffuse gas that fills the space between galaxies, and is so hot that it shines in X-ray light. The brightest X-rays come from so-called clusters of galaxies, the places in the Universe where the galaxies are packed closest together. ...

A Uniform Contribution of Core-Collapse and Type Ia Supernovae to the
Chemical Enrichment Pattern in the Outskirts of the Virgo Cluster - A. Simionescu et al

• Astrophysical Journal Letters 811(2):L25 (2015 Oct 01) DOI: 10.1088/2041-8205/811/2/L25
  arXiv.org > astro-ph > arXiv:1506.06164 > 19 Jun 2015 (v1), 07 Sep 2015 (v2)

[bystander]

Suzaku Finds Common Chemical Makeup at Largest Cosmic Scales
NASA Goddard Space Flight Center | 2015 Oct 26

[c][attachment=0]Suzaku_probes_Virgo_Cluster_labeled_print[1].jpg[/attachment][/c][hr][/hr]

A new survey of hot, X-ray-emitting gas in the Virgo galaxy cluster shows that the elements needed to make stars, planets and people were evenly distributed across millions of light-years early in cosmic history, more than 10 billion years ago.

The Virgo cluster, located about 54 million light-years away, is the nearest galaxy cluster and the second brightest in X-rays. The cluster is home to more than 2,000 galaxies, and the space between them is filled with a diffuse gas so hot it glows in X-rays.

Using Japan's Suzaku X-ray satellite, a team led by Aurora Simionescu, an astrophysicist at the Japan Aerospace Exploration Agency (JAXA) in Sagamihara, acquired observations of the cluster along four arms extending up to 5 million light-years from its center.

"Heavier chemical elements from carbon on up are produced and distributed into interstellar space by stars that explode as supernovae at the ends of their lifetimes," Simionescu said. This chemical dispersal continues at progressively larger scales through other mechanisms, such as galactic outflows, interactions and mergers with neighboring galaxies, and stripping caused by a galaxy's motion through the hot gas filling galaxy clusters.

Supernovae fall into two broad classes. Stars born with more than about eight times the sun's mass collapse under their own weight and explode as core-collapse supernovae. White dwarf stars may become unstable due to interactions with a nearby star and explode as so-called Type Ia supernovae.

These different classes of supernovae produce different chemical compositions. Core-collapse supernovae mostly scatter elements ranging from oxygen to silicon, while white dwarf explosions release predominantly heavier elements, such as iron and nickel. Surveying the distribution of these elements over a vast volume of space, such as a galaxy cluster, helps astronomers reconstruct how, when, and where they were produced. Once the chemical elements made by supernovae are scattered and mixed into interstellar space, they become incorporated into later generations of stars. ...