 |
|
Dwarf galaxies need dark matter too, U-M astronomers say
October 25, 2007ANN ARBOR, Mich.-Stars in dwarf spheroidal galaxies behave in a way that suggests the galaxies are utterly dominated by dark matter, University of Michigan astronomers have found.
Astronomy professor Mario Mateo and post-doctoral researcher Matthew Walker measured the velocity of 6,804 stars in seven dwarf satellite galaxies of the Milky Way: Carina, Draco, Fornax, Leo I, Leo II, Sculptor and Sextans. They found that, contrary to what Newton's law of gravity predicts, stars in these galaxies do not move slower the farther they are from their galaxy's core.
"These galaxies show a problem right from the center," Mateo said. "The velocity doesn't get smaller. It just stays the same, which is eerie."
Astronomers already know stars in spiral galaxies behave in a similar way. This research dramatically increases the available information about smaller galaxies, making it possible to confirm that the distribution of light and stars in them is not the same as the distribution of mass.
"We have more than doubled the amount of data having to do with these galaxies, and that allows us to study them in an unprecedented manner. Our research shows that dwarf galaxies are utterly dominated by dark matter, so long as Newtonian gravity adequately describes these systems," Walker said. Walker received his doctorate from U-M earlier this year and currently has a post-doctoral position at the University of Cambridge in the United Kingdom.
Dark matter is a substance astronomers have not directly observed, but they deduce it exists because they detect its gravitational effects on visible matter. Based on these measurements, the prevailing theory in astronomy and cosmology is that the visible parts of the universe make up only a fraction of its total matter and energy.
The planet Neptune was once "dark matter," Mateo said. Before the term was even coined, astronomers predicted its existence based on an anomaly in the orbit of Neptune's neighbor Uranus. They knew just where to look for Neptune.
For the past quarter century, astronomers have been looking for the Neptune of the universe, so to speak. Dark matter could take the form of dwarf stars and planets, elementary particles including neutrinos, or hypothetical and as-yet undetected particles that don't interact with visible light or other parts of the electromagnetic spectrum.
Dark matter is believed to hold galaxies together. The gravitational force of the visible matter is not considered strong enough to prevent stars from escaping. Other theories exist to explain these discrepancies, though. For example, Modified Newtonian Dynamics, Mateo said, proposes that gravitational forces become stronger when accelerations are very weak. While their results align with current dark matter models, Mateo and Walker say they also bolster this less-popular explanation.
"These dwarf galaxies are not much to look at," Mateo continued, "but they may really alter our fundamental views on the nature of dark matter and, perhaps, even gravity."
Walker will present a paper on these findings on Oct. 30 at the Magellan Science Meeting in Cambridge, Mass. The paper he will present is Velocity Dispersion Profiles of Seven Dwarf Spheroidal Galaxies. It was published in the Sept. 20 edition of Astrophysical Journal Letters.
University of Michigan
Astronomers already know stars in spiral galaxies behave in a similar way. This research dramatically increases the available information about smaller galaxies, making it possible to confirm that the distribution of light and stars in them is not the same as the distribution of mass.
"We have more than doubled the amount of data having to do with these galaxies, and that allows us to study them in an unprecedented manner. Our research shows that dwarf galaxies are utterly dominated by dark matter, so long as Newtonian gravity adequately describes these systems," Walker said. Walker received his doctorate from U-M earlier this year and currently has a post-doctoral position at the University of Cambridge in the United Kingdom.
Dark matter is a substance astronomers have not directly observed, but they deduce it exists because they detect its gravitational effects on visible matter. Based on these measurements, the prevailing theory in astronomy and cosmology is that the visible parts of the universe make up only a fraction of its total matter and energy.
The planet Neptune was once "dark matter," Mateo said. Before the term was even coined, astronomers predicted its existence based on an anomaly in the orbit of Neptune's neighbor Uranus. They knew just where to look for Neptune.
For the past quarter century, astronomers have been looking for the Neptune of the universe, so to speak. Dark matter could take the form of dwarf stars and planets, elementary particles including neutrinos, or hypothetical and as-yet undetected particles that don't interact with visible light or other parts of the electromagnetic spectrum.
Dark matter is believed to hold galaxies together. The gravitational force of the visible matter is not considered strong enough to prevent stars from escaping. Other theories exist to explain these discrepancies, though. For example, Modified Newtonian Dynamics, Mateo said, proposes that gravitational forces become stronger when accelerations are very weak. While their results align with current dark matter models, Mateo and Walker say they also bolster this less-popular explanation.
"These dwarf galaxies are not much to look at," Mateo continued, "but they may really alter our fundamental views on the nature of dark matter and, perhaps, even gravity."
Walker will present a paper on these findings on Oct. 30 at the Magellan Science Meeting in Cambridge, Mass. The paper he will present is Velocity Dispersion Profiles of Seven Dwarf Spheroidal Galaxies. It was published in the Sept. 20 edition of Astrophysical Journal Letters.
University of Michigan
Dark Matter News and Current Dark Matter Events RSSUCI scientists discover minimum mass for galaxies
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.
Clash of clusters provides new dark matter clue
A powerful collision between galaxy clusters has been captured by the NASA/ESA Hubble Space Telescope and NASA's Chandra X-ray Observatory. This clash of clusters provides striking evidence for dark matter and insight into its properties.
Study shows clumps and streams of dark matter in inner regions of the Milky Way
Using one of the most powerful supercomputers in the world to simulate the halo of dark matter that envelopes our galaxy, researchers found dense clumps and streams of the mysterious stuff lurking in the inner regions of the halo, in the same neighborhood as our solar system.
Hubble finds large sample of very distant galaxies
New Hubble Space Telescope observations of six spectacular galaxy clusters acting as gravitational lenses have given significant insights into the early stages of the Universe. Scientists have found the largest sample of very distant galaxies seen to date: ten promising candidates thought to lie at a distance of 13 billion light-years (~redshift 7.5).
Roadrunner supercomputer puts research at a new scale
Less than a week after Los Alamos National Laboratory's Roadrunner supercomputer began operating at world-record petaflop/s data-processing speeds, Los Alamos researchers are already using the computer to mimic extremely complex neurological processes.
UC Santa Cruz physicists eagerly await launch of NASA space telescope they helped build
When NASA launches its newest space observatory, physicists at the University of California, Santa Cruz, will be watching as the product of nearly 16 years of hard work blasts into orbit.
Searching the heavens
A new space mission, due to launch this month, is going to shed light on some of the most extreme astrophysical processes in nature - including pulsars, remnants of supernovae, and supermassive black holes.
Compact galaxies in early Universe pack a big punch
Using the Near Infrared Camera and Multi-Object Spectrometer onboard of the Hubble NASA/ESA Hubble Space Telescope, astronomers have made observations of young, surprisingly compact galaxies, each only 5,000 light-years across, but weighing 200 billion times the mass of the Sun.
Paranal Receives New Mirror
A 4.1-metre diameter primary mirror, a vital part of the world's newest and fastest survey telescope, VISTA (the Visible and Infrared Survey Telescope for Astronomy) has been delivered to its new mountaintop home at Cerro Paranal, Chile. The mirror will now be coupled with a small camera for initial testing prior to installing the main camera in June. Full scientific operations are due to start early next year. VISTA will form part of ESO's Very Large Telescope facility.
Delta II Rocket Coming Together for NASA's GLAST Satellite Launch
The Delta II 7920-H, or "Heavy," rocket that will launch NASA's Gamma-ray Large Area Telescope (GLAST) satellite is in the process of being assembled on Launch Pad 17-B at Cape Canaveral Air Force Station, Fla.
More Dark Matter News Articles
 | The Developing Mind: How Relationships and the Brain Interact to Shape Who We Are by Daniel J. Siegel This book goes beyond the nature and nurture divisions that traditionally have constrained much of our thinking about development, exploring the role of interpersonal relationships in forging key connections in the brain. Daniel J. Siegel presents a groundbreaking new way of thinking about the emergence of the human mind and the process by which each of us becomes a feeling, thinking, remembering... |
 | A Confederacy of Dunces by John Kennedy Toole "A green hunting cap squeezed the top of the fleshy balloon of a head. The green earflaps, full of large ears and uncut hair and the fine bristles that grew in the ears themselves, stuck out on either side like turn signals indicating two directions at once. Full, pursed lips protruded beneath the bushy black moustache and, at their corners, sank into little folds filled with disapproval and... |
 | Sailing the Wine-Dark Sea: Why the Greeks Matter (Hinges of History) by Thomas Cahill In Sailing the Wine-Dark Sea, his fourth volume to explore “the hinges of history,” Thomas Cahill escorts the reader on another entertaining—and historically unassailable—journey through the landmarks of art and bloodshed that defined Greek culture nearly three millennia ago.In the city-states of Athens and Sparta and throughout the Greek islands, honors could be won in... |
 | Wind Energy Basics: A Guide to Small and Micro Wind Systems by Paul Gipe The wind power industry has been transformed in the 1990s by dramatic breakthroughs in efficiency, economy, and adaptability. Wind Energy Basics is the most up-to-date source available of information about small wind systems. The book includes the unique "standard small wind turbine rating" developed by the author, which is designed to help readers wade through conflicting performance claims by... |
 | Touched with Fire: Manic-Depressive Illness and the Artistic Temperament by Kay Redfield Jamison The march of science in explaining human nature continues. In Touched With Fire, Jamison marshals a tremendous amount of evidence for the proposition that most artistic geniuses were (and are) manic depressives. This is a book of interest to scientists, psychologists, and artists struggling with the age-old question of whether psychological suffering is an essential component of artistic... |
 | Dark Side of the Universe: Dark Matter, Dark Energy, and the Fate of the Cosmos by Iain Nicolson Once we thought the universe was filled with shining stars, dust, planets, and galaxies. We now know that more than 98 percent of all matter in the universe is dark. It emits absolutely nothing yet bends space and time; keeps stars speeding around galaxies; and determines the fate of the universe. But dark matter is only part of the story. Scientists have recently discovered that the expansion of... |
 | Hubbert's Peak: The Impending World Oil Shortage by Kenneth S. Deffeyes Geophysicist M. King Hubbert predicted in 1956 that U.S. oil production would reach its highest level in the early 1970s. Though roundly criticized by oil experts and economists, Hubbert's prediction came true in 1970. In this revised and updated edition reflecting the latest information on the world supply of oil, Kenneth Deffeyes uses Hubbert's methods to find that world oil production will... |
 | From the Fryer to the Fuel Tank: The Complete Guide to Using Vegetable Oil as an Alternative Fuel by Joshua Tickell, Kaia Tickell From the Fryer to the Fuel Tank is the first and only book that details all aspects of running diesel engines on vegetable oil. Includes information on biodiesel, the diesel fuel substitute made from new or used vegetable as well as information on running any diesel engine on straight vegetable oil (SVO). This book is packed with history, information, instructions, photos, diagrams and resources.... |
 | Microhydro: Clean Power from Water by Scott Davis Hydroelectricity is the world's largest-and cleanest-source of renewable -energy. But despite lively interest in renewables generally, there is an information vacuum about the smallest version of the technology dubbed "the simplest, most reliable and least expensive way to generate power off grid." Highly illustrated and practical, Microhydro is the first complete book on the topic in a decade.... |
 | Dark Matter by S. W. Ahmed What if only a small fraction of the stars in our galaxy are visible to us, because the vast majority of star systems are teeming with aliens who wish to remain unseen? Marc Zemin, a brilliant student of astrophysics, is the first human to ever stumble upon this startling secret, when his experiments with wormhole travel cause aliens to land on Earth and whisk him away into space. The aliens want... |
| © 2008 BrightSurf.com |