Scientists discover minimum mass for galaxies

Aug 27, 2008
Satellite galaxies studied by UCI researchers that are within 500,000 light-years from the Milky Way.

(PhysOrg.com) -- By analyzing light from small, faint galaxies that orbit the Milky Way, UC Irvine scientists believe they have discovered the minimum mass for galaxies in the universe – 10 million times the mass of the sun.

This mass could be the smallest known "building block" of the mysterious, invisible substance called dark matter. Stars that form within these building blocks clump together and turn into galaxies.

Scientists know very little about the microscopic properties of dark matter, even though it accounts for approximately five-sixths of all matter in the universe.

"By knowing this minimum galaxy mass, we can better understand how dark matter behaves, which is essential to one day learning how our universe and life as we know it came to be," said Louis Strigari, lead author of this study and a McCue Postdoctoral Fellow in the Department of Physics and Astronomy at UCI.

Study results are published Aug. 28 in the journal Nature.

Dark matter governs the growth of structure in the universe. Without it, galaxies like our own Milky Way would not exist. Scientists know how dark matter's gravity attracts normal matter and causes galaxies to form. They also suspect that small galaxies merge over time to create larger galaxies such as our Milky Way.

The smallest known galaxies, called dwarf galaxies, vary greatly in brightness, from 1,000 times the luminosity of the sun to 10 million times the luminosity of the sun. At least 22 of these dwarf galaxies are known to orbit the Milky Way. UCI scientists studied 18 of them using data obtained with the Keck telescope in Hawaii and the Magellan telescope in Chile, with the goal of calculating their masses. By analyzing stars' light in each galaxy, they determined how fast the stars were moving. Using those speeds, they calculated the mass of each galaxy.

The researchers expected the masses to vary, with the brightest galaxy weighing the most and the faintest galaxy weighing the least. But surprisingly all dwarf galaxies had the same mass – 10 million times the mass of the sun.

Manoj Kaplinghat, a study co-author and physics and astronomy assistant professor at UCI, explains this finding using an analogy in which humans play the role of dark matter.

"Suppose you are an alien flying over Earth and identifying urban areas from the concentration of lights in the night. From the brightness of the lights, you may surmise, for example, that more humans live in Los Angeles than in Mumbai, but this is not the case," Kaplinghat said. "What we have discovered is more extreme and akin to saying that all metro areas, even those that are barely visible at night to the aliens, have a population of about 10 million."

Since dwarf galaxies are mostly dark matter – the ratio of dark matter to normal matter is as large as 10,000 to one – the minimum-mass discovery reveals a fundamental property of dark matter.

"We are excited because these galaxies are virtually invisible, yet contain a tremendous amount of dark matter," said James Bullock, a study co-author and director of UCI's Center for Cosmology. "This helps us better understand the particle that makes up dark matter, and it teaches us something about how galaxies form in the universe."

The scientists say clumps of dark matter may exist that contain no stars. The only dark matter clumps they can detect right now are those that are lit by stars.

Scientists hope to learn about dark matter's microscopic properties when the Large Hadron Collider in Switzerland becomes operational later this year. The device will accelerate two beams of nuclei in a ring in opposite directions and then slam them together to recreate conditions just after the Big Bang. By doing this, scientists hope to create the dark matter particle in the lab for the first time.

Provided by University of California - Irvine

Explore further: Quest for extraterrestrial life not over, experts say

add to favorites email to friend print save as pdf

Related Stories

Cosmologists weigh cosmic filaments and voids

6 hours ago

(Phys.org) —Cosmologists have established that much of the stuff of the universe is made of dark matter, a mysterious, invisible substance that can't be directly detected but which exerts a gravitational ...

Astronomers challenge Cosmological Model

Apr 03, 2014

(Phys.org) —Astronomers Professor Chris Collins and Dr Ian McCarthy from LJMU's Astrophysics Research Institute are challenging the view that the currently preferred cosmological model of the Universe is ...

Fermi data tantalize with new clues to dark matter

Apr 03, 2014

(Phys.org) —A new study of gamma-ray light from the center of our galaxy makes the strongest case to date that some of this emission may arise from dark matter, an unknown substance making up most of the ...

Recommended for you

Quest for extraterrestrial life not over, experts say

Apr 18, 2014

The discovery of an Earth-sized planet in the "habitable" zone of a distant star, though exciting, is still a long way from pointing to the existence of extraterrestrial life, experts said Friday. ...

Continents may be a key feature of Super-Earths

Apr 18, 2014

Huge Earth-like planets that have both continents and oceans may be better at harboring extraterrestrial life than those that are water-only worlds. A new study gives hope for the possibility that many super-Earth ...

Exoplanets soon to gleam in the eye of NESSI

Apr 18, 2014

(Phys.org) —The New Mexico Exoplanet Spectroscopic Survey Instrument (NESSI) will soon get its first "taste" of exoplanets, helping astronomers decipher their chemical composition. Exoplanets are planets ...

User comments : 7

Adjust slider to filter visible comments by rank

Display comments: newest first

mattytheory
3.3 / 5 (3) Aug 27, 2008
Thank you Alizee, you took the words right out of my mouth.
k_m
1 / 5 (4) Aug 28, 2008
And when did "dark matter" become fact?
yyz
not rated yet Aug 28, 2008
I agree w-Alizee that the lines between dwarf galaxy, globular cluster, extended cluster & ultra-compact dwarf are blurring & in need of qualitative & quantitative definitions. However, the mass limits on these small systems must be telling us something vital in our understanding of them & of DM itself. These observations only add to clues astrophysicists will need to make valid & useful models of both small intergalactic stellar associations & the nature of DM. Nature is trying to tell us something here (and it's not that DM theory is wrong, useless, fabricated, etc.).
seanpu
1 / 5 (3) Aug 29, 2008
DM and DE dont exist. shame really, they wasted their time with this.
earls
4 / 5 (1) Aug 29, 2008
seanpu doesn't exist
yyz
not rated yet Aug 29, 2008
I concur with earls, seanpu doesn't exist. Maybe AGM has an answer for this, and if not, I'm sure astrology does.
yyz
not rated yet Aug 29, 2008
The paper referred to in the article was posted today on the arXiv site. Entitled 'A common mass scale for satellite galaxies of the Milky Way' @ arXiv:0808.3772v1 . In the paper the authors conclude that tidal forces from our MWG were not the cause of their results. The 18 dwarf galaxies were all located at least 30kpc from the Milky Way. They suggest a form of Hot Dark Matter (as opposed to the more commonly used Cold Dark Matter [CDM] scenario) may be the cause of this monumental finding. I think their results are trying to tell us something very important about our universe & how it works. Anyway, congrats to the team that made these difficult observations & may they lead the way to a better understanding of DM in our universe.

More news stories

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Cosmologists weigh cosmic filaments and voids

(Phys.org) —Cosmologists have established that much of the stuff of the universe is made of dark matter, a mysterious, invisible substance that can't be directly detected but which exerts a gravitational ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.