Reconciling dwarf galaxies with dark matter

September 7, 2016, Carnegie Institution for Science
Andrew Wetzel's simulation shows stars in the Milky Way-like galaxy on the left and the same region's dark matter on the right. Credit: Andrew Wetzel.

Dwarf galaxies are enigmas wrapped in riddles. Although they are the smallest galaxies, they represent some of the biggest mysteries about our universe. While many dwarf galaxies surround our own Milky Way, there seem to be far too few of them compared with standard cosmological models, which raises a lot of questions about the nature of dark matter and its role in galaxy formation.

New theoretical modeling work from Andrew Wetzel, who holds a joint fellowship between Carnegie and Caltech, offers the most accurate predictions to date about the dwarf galaxies in the Milky Way's neighborhood. Wetzel achieved this by running the highest-resolution and most-detailed simulation ever of a galaxy like our Milky Way. His findings, published by The Astrophysical Journal Letters, help to resolve longstanding debates about how these dwarf galaxies formed.

One of the biggest mysteries of dwarf galaxies has to do with , which is why scientists are so fascinated by them.

"Dwarf galaxies are at the nexus of dark matter science," Wetzel said.

Dark matter makes up a quarter of our universe. It exerts a gravitational pull, but doesn't seem to interact with regular matter—like atoms, stars, and us—in any other way. We know it exists because of the gravitational effect it has on stars and gas and dust. This effect is why it is key to understanding . Without dark matter, galaxies could not have formed in our universe as they did. There just isn't enough gravity to hold them together without it.

A video explaining what dark matter is anyway, and why scientists are interested in it. Credit: John Strom and Andrew Wetzel

The role of dark matter in the formation of dwarf galaxies has remained a mystery. The standard cosmological model has told us that, because of dark matter, there should be many more dwarf galaxies out there, surrounding our own Milky Way, than we have found. Astronomers have developed a number of theories for why we haven't found more, but none of them could account for both the paucity of dwarf galaxies and their properties, including their mass, size, and density.

As observation techniques have improved, more dwarf galaxies have been spotted orbiting the Milky Way. But still not enough to align with predictions based on standard cosmological models.

So scientists have been honing their simulation techniques in order to bring theoretical modeling predictions and observations into better agreement. In particular, Wetzel and his collaborators worked on carefully modeling the complex physics of stellar evolution, including how supernovae—the fantastic explosions that punctuate the death of massive stars—affect their host galaxy.

With these advances, Wetzel ran the most-detailed simulation of a galaxy like our Milky Way. Excitingly, his model resulted in a population of dwarf galaxies that is similar to what astronomers observe around us.

As Wetzel explained: "By improving how we modeled the physics of stars, this new simulation offered a clear theoretical demonstration that we can, indeed, understand the dwarf galaxies we've observed around the Milky Way. Our results thus reconcile our understanding of dark matter's role in the universe with observations of dwarf galaxies in the Milky Way's neighborhood."

Despite having run the highest-resolution simulation to date, Wetzel continues to push forward, and he is in the process of running an even higher-resolution, more-sophisticated simulation that will allow him to model the very faintest dwarf galaxies around the Milky Way.

A video of images from the simulation

"This mass range gets interesting, because these 'ultra-faint' are so faint that we do not yet have a complete observational census of how many exist around the Milky Way. With this next simulation, we can start to predict how many there should be for observers to find," he added.

Explore further: Dark matter satellites trigger massive birth of stars

More information: Reconciling dwarf galaxies with LCDM cosmology: Simulating a realistic population of satellites around a Milky Way-mass galaxy, arxiv.org/abs/1602.05957

Related Stories

Dark matter satellites trigger massive birth of stars

March 9, 2016

One of the main predictions of the current model of the creation of structures in the universe, known at the Lambda Cold Dark Matter model, is that galaxies are embedded in very extended and massive halos of dark matter that ...

How a star cluster ruled out MACHOs

August 10, 2016

Are massive black holes hiding in the halos of galaxies, making up the majority of the universe's mysterious dark matter? This possibility may have been ruled out by a star cluster in a small galaxy recently discovered orbiting ...

Hubble spots an irregular island in a sea of space

August 29, 2016

This image, courtesy of the NASA/ESA Hubble Space Telescope's Advanced Camera for Surveys (ACS), captures the glow of distant stars within NGC 5264, a dwarf galaxy located just over 15 million light-years away in the constellation ...

Hubble peers at a distinctly disorganized dwarf galaxy

April 4, 2016

Despite being less famous than their elliptical and spiral galactic cousins, irregular dwarf galaxies, such as the one captured in this NASA/ESA Hubble Space Telescope image, are actually one of the most common types of galaxy ...

Recommended for you

Three 'super-Earths' orbiting a cool dwarf star discovered

January 23, 2018

Using NASA's prolonged Kepler mission, known as K2, astronomers have found three new "super-Earth" exoplanets. The newly detected alien worlds orbit the cool dwarf star designated LP415-17. The finding is reported January ...

Dust storms linked to gas escape from Martian atmosphere

January 23, 2018

Some Mars experts are eager and optimistic for a dust storm this year to grow so grand it darkens skies around the entire Red Planet. This type of phenomenon in the environment of modern Mars could be examined as never before ...

Scientist proposes new definition of a planet

January 23, 2018

Pluto hogs the spotlight in the continuing scientific debate over what is and what is not a planet, but a less conspicuous argument rages on about the planetary status of massive objects outside our solar system. The dispute ...

4 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

bschott
1.6 / 5 (7) Sep 07, 2016
. Without dark matter, galaxies could not have formed in our universe as they did. There just isn't enough gravity to hold them together without it.

An article a month ago described observations about how magnetic fields approximated gravity in a star forming region. It was rudimentary but none the less reasonably accurate from a physics standpoint, why the hell would size make a difference?If magnetic fields can "approximate gravity" on a molecular cloud/ star forming scale they can certainly do it on a stellar/galaxy forming scale. Both attractive and repulsive forces make modelling observed motion a lot easier than trying to model it based on matter that cannot be found and purely attractive force.

Ironically, one of the few guys who has a bit of a handle on the EM drive from a physics standpoint shares the same POV.
http://www.ibtime...-1565673
RichManJoe
3 / 5 (4) Sep 07, 2016
One risk of adjusting a model to get the desired answer is that the desired answer is wrong.
torbjorn_b_g_larsson
3.9 / 5 (7) Sep 07, 2016
Good news. But I note that the accompanying video takes up just a smidgen of all dark matter observations, there are collision results, galaxy cluster results, BAOs, the cosmological filaments and above all the CMB spectra. All structures from dwarf galaxies and up show D, consistently.

@bs: Can you give a reference? Magnetism is often a fudge factor, and it is hard to exclude. Matter and especially dark matter are not such, since they are global observations.

@RMJ: You mean detail the model to see if the observed behavior is possible. In this case it was, and it was natural too boot. Not that you expect from, say, bs's possible magnetic fudge above.

Let me turn that around: one risk of a lazy description of science to get the desired answer - that science is guessing - is that the desired answer is wrong.
bschott
1 / 5 (3) Sep 08, 2016
@bs: Can you give a reference?

http://phys.org/n...ion.html
@TBGL - DM is the fudge factor, not magnetism. You are confused about what we actually know exists, use every day and all stable particle physics is based on (magnetism), vs. observations you are pigeon holing as evidence of DM by claiming gravity is responsible for organizing all we see.
Matter and especially dark matter are not such, since they are global observations.

No one has ever OBSERVED dark matter....ever. Effects which are attributed to DM do not validate the assumption that it is a particle or that it's effect is gravitational, your belief and math are the only places DM as a particle exists. The universe shows us how it works, ostriches with their heads buried in the DM sand are the only ones who can't see it.

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.