Researchers use network theory to solve the mystery of stellar initial mass function

June 7, 2016, Lomonosov Moscow State University
A model of the interstellar medium having a fractal density distribution. Dense cores where proto-stars are forming are marked and gravitational forces generated by them are shown. Credit: Igor Chilingarian, Andrei Klishin

For the first time, scientists have used methods of network science to solve a fundamental astrophysical problem—explaining the so-called "stellar initial mass function," a distribution of stars by mass in galaxies and star clusters. The study has been published in the recent issue of The Astrophysical Journal.

University of Michigan graduate student Andrei Klishin, under the supervision of Igor Chilingarian of the Sternberg Astronomical Institute, Moscow State University and Smithsonian Astrophysical Observatory, applied methods of network science to solve the 60-year-old astronomical problem. "Such methods have been used across different research fields, from sociology and information science to molecular biology, but never before in astrophysics," Igor Chilingarian says.

The stellar describes the relative fractions of stars with different masses in a stellar system or a ratio of big and small stars in galaxies. In 1955, the theoretical physicist and astrophysicist Edwin Salpeter was the first to derive this distribution law empirically in the stellar neighborhood using star counts (presently known as the "Salpeterinitial mass function"). He demonstrated that the distribution of stars by mass has the shape of a power law with exponent of -2.35, i.e. the stars 10 times more massive than our sun are 102.35 = 220 times less numerous than solar-type stars.

How, exactly, stars in a galaxy or a star cluster are distributed by mass is crucially important for astronomers. A stellar system is like a big family in which all members interact. They delineate the "living space" in a certain way and react to external influences according to the same physical laws. In order to better understand how members of that family affect each other's evolution, astronomers need to know what types of stars the family consists of—i.e., to know how many stars of each mass there are in the system.

Igor Chilingarian and Andrei Klishin described a system of proto-stars that evolve by absorbing gas from the diffuse interstellar medium as a spatial network growing by the principle of preferential attachment: A node having many links creates new links even faster. In the , links are gravitational forces acting between molecular dense cores that will later form stars. "We demonstrated that a power law that governs stellar initial mass function arises independently of the initial mass distribution of proto-stars if the density distribution in the interstellar cloud is fractal. This fractal distribution directly follows from the classical theory of turbulence developed by the Soviet mathematician Andrey Kolmogorov. We encounter fractal, or self-similar objects on a daily basis. Among others, clouds in Earth's atmosphere, snowflakes, and even some fruits and vegetables, such as cauliflower or broccoli, demonstrate fractal properties," says Igor Chilingarian.

The same region of the interstellar medium as shown in Figure 1with basins of gravitational attraction by each dense core marked witha different color. A small parcel of the interstellar medium shown asa little square can join any dense core with a probability proportional to the gravitation acceleration towards that core. Credit: Igor Chilingarian, Andrei Klishin

In the framework of this simple model, the scientists theoretically explained the stellar initial mass function shape in just eight equations, which did not invoke any unjustified assumptions or require extra free parameters of many existing star formation theories. Igor Chilingarian emphasizes that all existing initial mass function theories were developed using "a classical astrophysical approach" and presented in long articles featuring dozens of pages of calculations and hundreds of formulae.

"Igor invited me to work on this project after we met in Boston, when I mentioned my interests in statistical physics," Andrei Klishin says. "This area of physics deals with the aspects of systems of large numbers of particles where particular details regarding individual particles become unimportant. We know that the same Salpeter exponent of -2.35 was measured in many star clusters of different ages, metallicities and total masses. This suggests that the value is determined not by some local properties of a specific cluster, but rather by some more general principle. That's why when we introduce the principle of preferential attachment in our paper, we refer to works in network science, bibliometrics, biological speciation. In all those very different systems, the statistical properties turn out to be very similar."

Cauliflower is an example of an everyday object with fractal properties having the dimensionality similar to theinterstellar medium Credit: Igor Chilingarian, Rasbak

Network science is a modern area of research that researchers developed over the last 15 to 20 years. As suggested by its name, it studies properties of networks as mathematical objects, regardless of the specific system interpreted as a network. Network theory can, for instance, describe power grids as a set of power plants, loads and transmission lines; it also describes the interactions of a multitude of proteins in a living organism, connections of users in a social network such as Facebook or even the entire web, or communications in scientific collaborations. Igor Chilingarian and Andrei Klishin were the first to apply methods to solve a fundamental astrophysical problem.

"This work is the first of its kind, and it creates a basis for a new interdisciplinary approach in astrophysics. We plan to further develop this family of methods and use them to study a broad spectrum of astrophysical phenomena in aspects of star formation and in observational cosmology, such as a study of the large-scale structure of matter distribution in the universe," says Igor Chilingarian.

Explore further: How do massive young star clusters form?

More information: Andrei A. Klishin et al, EXPLAINING THE STELLAR INITIAL MASS FUNCTION WITH THE THEORY OF SPATIAL NETWORKS, The Astrophysical Journal (2016). DOI: 10.3847/0004-637X/824/1/17

Related Stories

How do massive young star clusters form?

April 8, 2016

Young massive star clusters are systems of stars with more than about ten thousand solar-masses of material and ages less than about one hundred million years that are gravitationally bound together. In these clusters the ...

Other suns got the right spin

May 17, 2016

Astrophysicists from the Leibniz Institute for Astrophysics Potsdam (AIP) and the Johns Hopkins University in Baltimore have for the first time measured the rotation periods of stars in a cluster nearly as old as the sun ...

Understanding Spica (Alpha Virginis)

April 25, 2016

The familiar star Spica (Alpha Virginis) is the fifteenth brightest star in the night sky, in part because it is relatively nearby, only about 250 light-years away. It is easy to find by following the arc of the Big Dipper's ...

Astronomers find runaway galaxies

April 23, 2015

We know of about two dozen runaway stars, and have even found one runaway star cluster escaping its galaxy forever. Now, astronomers have spotted 11 runaway galaxies that have been flung out of their homes to wander the void ...

The ages of sun-like stars

February 6, 2015

The mass of a star is perhaps its most significant feature. It determines how brightly it shines (a star ten times more massive than the Sun will, during its normal lifetime, shine about forty million times brighter than ...

Recommended for you

Astronomers find possible elusive star behind supernova

November 15, 2018

Astronomers may have finally uncovered the long-sought progenitor to a specific type of exploding star by sifting through NASA Hubble Space Telescope archival data and conducting follow-up observations using W. M. Keck Observatory ...

Gravitational waves from a merged hyper-massive neutron star

November 14, 2018

For the first time astronomers have detected gravitational waves from a merged, hyper-massive neutron star. The scientists, Maurice van Putten of Sejong University in South Korea, and Massimo della Valle of the Osservatorio ...

The dance of the small galaxies that surround the Milky Way

November 14, 2018

An international team led by researchers from the IAC used data from the ESA satellite Gaia to measure the motion of 39 dwarf galaxies. This data gives information on the dynamics of these galaxies, their histories and their ...


Adjust slider to filter visible comments by rank

Display comments: newest first

2 / 5 (4) Jun 07, 2016
Gravity attraction, what about magnetic attraction of atoms to each other based a their dominant quantum charges in the construction of a dominant positive atom or heavy element atoms that are over loaded with neutrons and orbiting electrons that give the atom a dominant negative charge of its quantum mass construction, these would would inter act to each building clusters of atoms to build mass with magnetic attraction of magnetic compression of clusters in initial constructions of mass for star formation, gravity is a construction of mass concentrated mass has more gravity than spread out mass like a gas clouds, concentrations in atoms clusters is the heart of gravitation in gas clouds ,
2 / 5 (4) Jun 10, 2016
It would really behoove the mods on here to have a "clean out the EU horseshit" day and just identify the 4 or so independent accounts that only come here to troll and are never responsive, and their socks.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.