Researchers use stars to infer mass of Milky Way

June 2, 2015, Columbia University
Northern Hemisphere of the sky as seen by the Sloan Digital Sky Survey. Stellar streams stick out from the vast number of stars in this view, of which most lie within the Milky Way disk. The Palomar 5 stream is the densest of the stellar streams discovered so far and turned out to be a perfect scale and yardstick for our understanding of the Milky Way. Credit: Ana Bonaca

What if your doctor told you that your weight is somewhere between 100 and 400 lbs.? With any ordinary scale every patient can do better at home. Yet, one patient can't: the Milky Way. Even though today we peer deeper into space than ever before, our home galaxy's weight is still unknown to about a factor of four. Researchers at Columbia University's Astronomy Department have now developed a new method to give the Milky Way a more precise physical checkup.

The Milky Way consists of roughly 100 billion stars that form a huge stellar disk with a diameter of 100-200 thousand light years. The Sun is part of this structure, hence, when we look into the sky, we look right into a gigantic disk of stars. The vast number of stars and the huge extent on the sky make it hard to measure fundamental quantities for the Milky Way, such as its weight.

An international team of scientists led by Columbia University researcher Andreas Küpper used stars outside this disk, which orbit around the Milky Way in a stream-like structure, to weigh the Milky Way to high precision. In a new study published in The Astrophysical Journal, the team demonstrates that such streams, produced by dissolving , can be used to measure not only the weight of our Galaxy, but can also be exploited as yardsticks to determine the location of the Sun within the Milky Way.

"Globular clusters are compact groups of thousands to several millions of stars that were born together when the universe was still very young," said Küpper. "They orbit around the Milky Way and slowly disintegrate over the course of billions of years, leaving a unique trace behind. Such star streams stick out from the rest of the stars in the sky as they are dense and coherent, much like contrails from airplanes easily stick out from regular clouds."

The researchers used data from the Sloan Digital Sky Survey, which scanned the sky of the Northern Hemisphere for about 10 years to create a comprehensive catalog of stars in the sky. The stream they tested the new technique on was produced by a globular cluster named Palomar 5, and had already been discovered in 2001 high above the Galactic disk. Eduardo Balbinot, coauthor on the current study from the University of Surrey in England, revisited the Sloan data and detected density wiggles in the stream of Palomar 5.

"We found the wiggles to be very pronounced and regularly spaced along the stream," said Balbinot. "Such variations cannot be random."

It is these wiggles that allow the researchers to gain the unprecedented precision of their measurement. Using the Yeti supercomputer of Columbia University, they created several million models of the stream in different realizations of the Milky Way. From these models and from comparing the wiggle pattern of the models to the observations, they were able to infer the mass of the Milky Way within a radius of 60,000 light years to be 210 billion times the mass of the Sun with an uncertainty of only 20 percent. The unique pattern of the density wiggles helped significantly to rule out models of the Milky Way, which were either too heavy or too skinny.

"An important advance in this work was using robust statistical tools - the same ones used to study changes in the genome and employed by to rank websites," explained Ana Bonaca, a coauthor from Yale University. This rigorous approach helped in achieving the high precision in weighing the Milky Way."

"Such measurements have been tried before with different streams, but the results were always quite ambiguous," added Professor Kathryn Johnston, coauthor of the study and chair of the Columbia Astronomy Department. "Our new measurement breaks these ambiguities by exploiting the unique density pattern that Palomar 5 created as it orbited around the Milky Way for the past 11 billion years."

In the future, the researchers aim to use more structures like the Palomar 5 stream to gain an even higher precision and to create the most realistic model of the Milky Way to date. From the improved precision the scientists hope to learn about the formation and composition of our home galaxy, and to understand how the Milky Way compares with other galaxies in the Universe. So far, the results indicate that the Milky Way is a healthy patient - neither too skinny nor too heavy for its size.

Explore further: For the Milky Way, it's snack time

More information: Globular Cluster Streams as Galactic High-Precision Scales - the Poster Child Palomar 5, The Astrophysical Journal, 2015.

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11 comments

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Tuxford
1.5 / 5 (16) Jun 02, 2015
"Globular clusters are compact groups of thousands to several millions of stars that were born together when the universe was still very young," said Küpper. "They orbit around the Milky Way and slowly disintegrate over the course of billions of years, leaving a unique trace behind. Such star streams stick out from the rest of the stars in the sky as they are dense and coherent, much like contrails from airplanes easily stick out from regular clouds."


ASSUMPTION, from another confused merger maniac married to the Huge Bang Fantasy.
yyz
4.4 / 5 (14) Jun 02, 2015
"ASSUMPTION, from another confused merger maniac blah, blah, blah...."

Sorry Tux, tidal tails from the globular cluster Palomar 5 are *observed*:

http://fr.arxiv.o.../0603062

http://fr.arxiv.o.../0307446

The only ASS here is you.
Psilly_T
2 / 5 (4) Jun 02, 2015


ASSUMPTION, from another confused merger maniac married to the Huge Bang Fantasy.

confused maniac married to dead discredited ideas.
Tuxford
1.4 / 5 (11) Jun 02, 2015
Back in your corner z. You will be embarrassed by your record of previous staunch defense of the fantasy. As I have previously stated, you can read, but cannot think.

No argument about tidal tales.... Again you missed the point, of the first sentence, not the last.
cantdrive85
1.4 / 5 (10) Jun 02, 2015
Tidal tails? No, plasma tubes (Birkeland currents) powering the clusters.
Vietvet
4.5 / 5 (8) Jun 02, 2015
If we can't even find 90% of the expected mass of the universe (thereby leading to the dark matter postulation) how can we expect to accurately measure the mass of our own galaxy? I don't think it is possible.



We all know you can't think.
ViperSRT3g
not rated yet Jun 03, 2015
210 Billion Solar Masses? If I am not mistaken, wouldn't this make the milky way twice the mass of Andromeda!? Or am I horribly confused in my sleep-deprived state? I know the whole number is still somewhat up in the air, but twice the size?
Captain Stumpy
5 / 5 (6) Jun 03, 2015
you can read, but cannot think
@tux
no, the problem lies in your assumption that your conjecture has scientific validity

yyz linked evidence that is based upon observed and empirical data which is how science works... not because someone said so, like cd's post

Tidal tails? No, plasma tubes (Birkeland currents) powering the clusters.
@cd
where is the empirical evidence supporting the conclusion that plasma tubes are powering the clusters?
where is the empirical evidence that birkeland currents is the official name etc?

linking conjecture without evidence is like your statements that the moon craters were made by plasma discharge even though we've OBSERVED meteors hitting the moon

eu is PSEUDOSCIENCE, not science
Tuxford
1.6 / 5 (7) Jun 03, 2015
you can read, but cannot think
@tux
no, the problem lies in your assumption that your conjecture has scientific validity


Cap, science will get there. Not understanding is no excuse for invalidity. Your statement is another assumption based on non-comprehension comforting for your limited understanding. It seems quite common for intellectuals to assume they are fully competent. Satisfies the ego. Breakthroughs are often not recognized by science until afterwards, otherwise there would be no progress.
Captain Stumpy
5 / 5 (4) Jun 06, 2015
Not understanding is no excuse ...Your statement is another assumption...your limited understanding.
@tux
no, i understood you quite well
and like i said: just because you can present a conjecture (or even a logical sounding argument) doesn't mean you can state that it is empirical nor can you validate the claim as being scientific or following the scientific method

a claim has equal authority and the same validity as stating "Fairy farts cause hurricanes, but Dwarf belches cause Cyclones"
Satisfies the ego
i don't care about the ego: mine or anyone elses
i follow the evidence
that is one reason i made such an effective investigator
Breakthroughs are often not recognized by science until afterwards
and ALL have needed the exact same requirements:
validated empirical evidence

claiming it is true is NOT valid or empirical
so we are back to the original point

the problem lies in your ASSumption that your conjecture has scientific validity
Captain Stumpy
5 / 5 (5) Jun 06, 2015
@Captain Stumpy: actually, "the EU" is more akin to a fundamentalist religious cult (and an anti-science one to boot) than pseudoscience.
@JeanTate
absolutely
in fact, i've often mentioned this very thing to cantdrive when he brings up his argument about "astrophysicists don't know plasma physics" or the one when he states "there is no such thing as magnetic reconnection"

regardless of the empirical evidence or the proof given to them, they always
ALWAYS
repeat the exact same argument later on PO as though there was some validity to it
(validation through repetition, just like religion)

https://www.googl...phys.org

About 484 results (0.70 seconds)

a deep rabbit hole indeed

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