Is the Milky Way an 'outlier' galaxy? Studying its 'siblings' for clues

Is the Milky Way an 'outlier' galaxy? Studying its 'siblings' for clues
Three-color optical image of a Milky Way sibling. Credit: Sloan Digital Sky Survey

The most-studied galaxy in the universe—the Milky Way—might not be as "typical" as previously thought, according to a new study.

The Milky Way, which is home to Earth and its solar system, is host to several dozen smaller galaxy satellites. These smaller galaxies orbit around the Milky Way and are useful in understanding the Milky Way itself.

Early results from the Satellites Around Galactic Analogs (SAGA) Survey indicate that the Milky Way's satellites are much more tranquil than other systems of comparable luminosity and environment. Many satellites of those "" galaxies are actively pumping out new stars, but the Milky Way's satellites are mostly inert, the researchers found.

This is significant, according to the researchers, because many models for what we know about the universe rely on galaxies behaving in a fashion similar to the Milky Way.

"We use the Milky Way and its surroundings to study absolutely everything," said Yale astrophysicist Marla Geha, lead author of the paper, which appears in the Astrophysical Journal. "Hundreds of studies come out every year about dark matter, cosmology, star formation, and galaxy formation, using the Milky Way as a guide. But it's possible that the Milky Way is an outlier."

The SAGA Survey began five years ago with a goal of studying the galaxies around 100 Milky Way siblings. Thus far it has studied eight other Milky Way sibling systems, which the researchers say is too small of a sample to come to any definitive conclusions. SAGA expects to have studied 25 Milky Way siblings in the next two years.

Yet the already has people talking. At a recent conference where Geha presented some of SAGA's initial findings, another researcher told her, "You've just thrown a monkey wrench into what we know about how small form."

"Our work puts the Milky Way into a broader context," said SAGA researcher Risa Wechsler, an astrophysicist at the Kavli Institute at Stanford University. "The SAGA Survey will provide a critical new understanding of and of the nature of ."

Wechsler, Geha, and their team said they will continue to improve the efficiency of finding satellites around Milky Way siblings. "I really want to know the answer to whether the Milky Way is unique, or totally normal," Geha said. "By studying our siblings, we learn more about ourselves."

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More information: "The SAGA Survey: I. Satellite Galaxy Populations Around Eight Milky Way Analogs," Marla Geha et al., 2017 Sept. 20, Astrophysical Journal … 847/1538-4357/aa8626 , Arxiv:
Journal information: arXiv , Astrophysical Journal

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Sep 21, 2017
Well, nice to see someone is enthusiastic about their work.

However, not only did they put the cart before the horse. But they haven't yet put the wheels of evidence on the cart. Nor caught the horse. Which is gleefully galloping around the barn, laughing at all us smug casuists. As we declaim to the Universe the rules 'WE' think it should observe.

This paper of pompous conclusions announced, is only the first chapter, in what will (hopefully) be a very thick book of knowledge to come.

Sep 22, 2017
rrwillsj, so you'd rather not know the preliminary results?

Sep 22, 2017
DS, yes, I do want to read of the preliminary results.

However, I am perturbed that the writers of this article would stick their professional necks out at this EARLY stage of their research. Crowing that this 'preliminary' work is definitive proof of hypothetical speculations!

Sep 26, 2017
I don't think they're saying that. They're not saying "x doesn't look like y, so z is definitive proof of w". No, they're simply stating that when comparing the Milky Way system to the 8 analogs studied so far, ours seems quieter. They're saying that in the future, potentially, we'll get a better picture.

From the abstract: "We find that the majority of satellites (26 of 27) are star-forming. These early results indicate that the Milky Way has a different satellite population than typical in our sample, potentially changing the physical interpretation of measurements based only on the Milky Way's satellite galaxies."

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