New paper shines light on little-understood process in astronomy

October 9, 2015, Texas Tech University
Figure showing the different size scales of accreting objects. Credit: Simone Scaringi

A paper coauthored by Tom Maccarone, a Texas Tech University associate professor in the Department of Physics, studies one of the most important but least understood processes in astronomy: accretion, or the growth in mass of an object by gravitationally collecting material from its surroundings.

The article, titled "Astrophysical accretion is a universal process in objects from proto-stars to supermassive black holes," is published in the most recent issue of the journal Science Advances.

"In our paper, we discovered a relationship that spans the range of different types of accreting objects, from proto-stars, much like our sun was at its time of birth, to white dwarfs to supermassive black holes with a billion times the mass of the sun located in galaxies millions of light-years away," Maccarone said. "In these systems there is some characteristic timescale for the variability – typically the large brightenings and fadings occur with that timescale. What we have found is that two important properties of the object are its physical size scale and the rate at which it is accreting matter."

The paper discussed a unified scenario for understanding brightness variations from around different types of stars and stellar remnants. Previous work unified the variability in disks around of different mass ranges, but now scientists can bring in accreting and even proto-stars by considering not just the mass of the star but also its size.

"Interestingly, there is no evidence the of the object affects the timescale," Maccarone said. "That the objects all fit on a universal scale suggests that the process of infall of matter is a universal process. Until recently, there has been relatively little discussion between the scientists who try to understand how proto-stars grow and the scientists who try to understand how grow, but these findings suggest that there should be."

An accretion disc around a black hole. Credit: University of Leicester

The study's lead author is Simone Scaringi, a Humboldt Research Fellow at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. The earliest ideas for this study came about when Scaringi visited Maccarone in Lubbock during the summer of 2014.

"I've known him for about a decade, since he was a student at my previous institution, and he and I have been working together for about four years," Maccarone said. "It is often just good to visit and talk face to face with collaborators, and that was his main motivation for coming out here."

Explore further: How massive can black holes get?

More information: "Accretion-induced variability links young stellar objects, white dwarfs, and black holes," Science Advances,

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5 / 5 (1) Oct 09, 2015
Would not the accretion be a function of the surroundings?
5 / 5 (3) Oct 10, 2015
cue tuxford.
1 / 5 (7) Oct 10, 2015
The problematic assumption is that accretion is fundamentally gravitational. The images returned back by Herschel reveal a branching filamentary pattern that was not expected by the radial force of gravity. To just continue on with adapting gravity to these observations is a questionable formulaic approach. The ESA used the term "ubiquitous" filaments, and on all scales, to describe this filamentary network. This is pretty much what Alfven predicted. The James Webb Space Telescope will continue to challenge these textbook accretion theories, but as we can already see, the theorists themselves will do all they can to resist an open-minded reaction to the data.
5 / 5 (4) Oct 10, 2015
Hyperfuzzy: To an extent. This study assumes that there is an accretion disk. If the surrounding mass density is too low, there won't be a significant disk, and the matter will flow straight in.

You can see the same thing in a sink or bathtub. If there is only a little water, such as from a slightly opened tap, the water runs straight into and down the drain. Above a certain rate, the water backs up, and starts circling the drain, the same effect as an accretion disk.

In the astronomical case, if the infall rate is extremely high, the disk becomes unstable, and "clumps" of matter can fall in from the inner edge. This can produce large flares, while the more normal infall is a fairly steady flow, resulting in the variability studied in this paper.
5 / 5 (3) Oct 12, 2015
The ESA used the term "ubiquitous" filaments, and on all scales, to describe this filamentary network. This is pretty much what Alfven predicted. -plasmasrevenge, a.k.a. hannesalfven

"But there is more: these observations revealed that filaments, which may extend to several light-years in length, appear to have a universal width of about one third of a light year. This suggests that something fundamental is lurking underneath." And yet the Church of EU has always insisted that electrical phenomena are scalable from the smallest lab experiment to the largest galaxy cluster. The universal width of filaments flies in the face of this notion. And your claim of "all scales," if you were intending to apply it to the length of a filament rather than its width, contradicts the "extends to several light years." Instead of all scales, there's an upper limit.

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