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Exiled Stars Explode Far From Home
Artist’s concept. Image by Dr. Alex H Parker, NASA and the SDSS
Sharp images obtained by the Hubble Space Telescope confirm that three supernovae discovered several years ago exploded in the dark emptiness of intergalactic space, having been flung from their home galaxies millions or billions of years earlier.
Most supernovae are found inside galaxies containing hundreds of billions of stars, one of which might explode per century per galaxy.
These lonely supernovae, however, were found between galaxies in three large clusters of several thousand galaxies each. The stars’ nearest neighbors were probably 300 light years away, nearly 100 times farther than our sun’s nearest stellar neighbor, Proxima Centauri, 4.24 light years distant.
uch rare solitary supernovae provide an important clue to what exists in the vast empty spaces between galaxies, and can help astronomers understand how galaxy clusters formed and evolved throughout the history of the universe.
Galactic Herding: New Image Brings Galaxy Diversity To Life
Image credit: Gemini Observatory/AURA
Galaxy groups are the most evident structures in the nearby universe. They are important laboratories for studying how galaxies form and evolve beyond our own Local Group of galaxies, which includes the Milky Way and the Great Spiral in Andromeda. Exploring the nature of these extragalactic “herds” may help to unlock the secrets to the overall structure of the universe.
Unlike animal herds, which are generally the same species traveling together, most galaxies move through space in associations comprised of myriad types, shapes, and sizes. Galaxy groups differ in their richness, size, and internal structure as well as the ages of their members. Some group galaxies are composed mainly of ancient stars, while others radiate with the power and splendor of youth.
These facts raise important questions for astronomers: Do all the galaxies in a group share a common origin? Are some just chance alignments? Or do galaxy groups pick up “strays” along the way and amalgamate them into the group?
NOAO: Compact Galaxy Groups Reveal Details Of Their Close Encounters
Credit: Dane Kleiner
Galaxies – spirals laced with nests of recent star formation, quiescent ellipticals composed mainly of old red stars, and numerous faint dwarfs – are the basic visible building blocks of the Universe. Galaxies are rarely found in isolation, but rather in sparse groups – sort of galactic urban sprawl. But there are occasional dense concentrations, often found in the center of giant clusters, but also, intriguingly, as more isolated compact groups (and yes, called Compact Galaxy Groups or CGs). The galaxies in these Compact Groups show dramatic differences in the way they evolve and change with time compared with galaxies in more isolated surroundings. Why is this? Collisions between galaxies in these dense groups are common, leading to rapid star formation, but there seems to be more to the puzzle.
A team led by Dr Iraklis Konstantopoulos of the Australian Astronomical Observatory (AAO) has now obtained spectacular images of some CGs with the Dark Energy camera attached to the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). This camera, constructed at the U.S. Department of Energy’s Fermi National Accelerator Laboratory, is able to image large areas of the sky to unprecedented faint limits. The team aims to combine these images with spectroscopic data from the AAO that will reveal the velocities of the galaxies, leading to a much better understanding of their gravitational interactions.
Four New Galaxy Clusters Take Researchers Further Back In Time
Four unknown galaxy clusters each potentially containing thousands of individual galaxies have been discovered some 10 billion light years from Earth.
An international team of astronomers, led by Imperial College London, used a new way of combining data from the two European Space Agency satellites, Planck and Herschel, to identify more distant galaxy clusters than has previously been possible. The researchers believe up to 2000 further clusters could be identified using this technique, helping to build a more detailed timeline of how clusters are formed.
Galaxy clusters are the most massive objects in the universe, containing hundreds to thousands of galaxies, bound together by gravity. While astronomers have identified many nearby clusters, they need to go further back in time to understand how these structures are formed. This means finding clusters at greater distances from the Earth.
The light from the most distant of the four new clusters identified by the team has taken over 10 billion years to reach us. This means the researchers are seeing what the cluster looked like when the universe was just three billion years old.
Crowdsourcing The Cosmos: Astronomers Welcome All To Identify Star Clusters In Andromeda Galaxy
Credit: Robert Gendler
Astronomers are inviting the public to search Hubble Space Telescope images of the Andromeda galaxy to help identify star clusters and increase understanding of how galaxies evolve.
The new Andromeda Project, set to study thousands of high-resolution Hubble images, is a collaboration among scientists at the University of Washington, the University of Utah and several other partners.
“It’s an amazing opportunity to discover something new,” said Julianne Dalcanton, UW astronomy professor. “Anyone can look at these beautiful Hubble images and participate in the scientific process. And it’s a huge help to us.”
Full Story: http://www.washington.edu/news/2012/12/04/crowdsourcing-the-cosmos-astronomers-welcome-all-to-identify-star-clusters-in-andromeda-galaxy/
Also: http://unews.utah.edu/news_releases/andromeda-wants-you/
Discovery of the Musket Ball Cluster
Image Credits: X-ray: NASA/CXC/UCDavis/W.Dawson et al; Optical: NASA/STScI/UCDavis/W.Dawson et al.
Using a combination of powerful observatories in space and on the ground, astronomers have observed a violent collision between two galaxy clusters in which so-called normal matter has been wrenched apart from dark matterthrough a violent collision between two galaxy clusters.
The newly discovered galaxy cluster is called DLSCL J0916.2+2951. It is similar to the Bullet Cluster, the first system in which the separation of dark and normal matter was observed, but with some important differences. The newly discovered system has been nicknamed the “Musket Ball Cluster” because the cluster collision is older and slower than the Bullet Cluster.
Full Story: http://www.chandra.harvard.edu/photo/2012/musketball/
Getting a Full Picture of an Elusive Subject
Two teams of astronomers have used data from NASA’s Chandra X-ray Observatory and other telescopes to map the distribution of dark matter in a galaxy cluster known as Abell 383, which is located about 2.3 billion light years from Earth. Not only were the researchers able to find where the dark matter lies in the two dimensions across the sky, they were also able to determine how the dark matter is distributed along the line of sight.
Dark matter is invisible material that does not emit or absorb any type of light, but is detectable through its gravitational effects. Several lines of evidence indicate that there is about six times as much dark matter as “normal,” or baryonic, matter in the Universe. Understanding the nature of this mysterious matter is one of the outstanding problems in astrophysics.
Galaxy clusters are the largest gravitationally-bound structures in the universe, and play an important role in research on dark matter and cosmology, the study of the structure and evolution of the universe. The use of clusters as dark matter and cosmological probes hinges on scientists’ ability to use objects such as Abell 383 to accurately determine the three-dimensional structures and masses of clusters.
Full Story: http://www.nasa.gov/mission_pages/chandra/multimedia/abell383.html
Hubble Pinpoints Farthest Protocluster of Galaxies Ever Seen
Using NASA’s Hubble Space Telescope, astronomers have uncovered a cluster of galaxies in the initial stages of development. It is the most distant such grouping ever observed in the early universe.
In a random sky survey made in near-infrared light, Hubble found five tiny galaxies clustered together 13.1 billion light-years away. They are among the brightest galaxies at that epoch and very young — existing just 600 million years after the big bang.
Galaxy clusters are the largest structures in the universe, comprising hundreds to thousands of galaxies bound together by gravity. The developing cluster, or protocluster, is seen as it looked 13 billion years ago. Presumably, it has grown into one of today’s massive “galactic cities,” comparable to the nearby Virgo cluster of more than 2,000 galaxies.
“These galaxies formed during the earliest stages of galaxy assembly, when galaxies had just started to cluster together,” said Michele Trenti of the University of Colorado at Boulder and the Institute of Astronomy at the University of Cambridge in the United Kingdom. “The result confirms our theoretical understanding of the buildup of galaxy clusters. And, Hubble is just powerful enough to find the first examples of them at this distance.”
Full Story: http://hubblesite.org/newscenter/archive/releases/2012/05
Ultra-Compact Dwarf Galaxies Are Bright Star Clusters
Astronomy & Astrophysics is publishing a new statistical study of the so-called ‘ultra-compact dwarf galaxies’ (UCDs), which are still mysterious objects. A team of astronomers has investigated how many of these UCDs exist in nearby galaxy clusters and groups. They show that the properties of UCDs match those of bright star clusters.
Astronomy & Astrophysics is publishing the results of a detailed investigation of how many ‘ultra-compact dwarf galaxies’ (UCDs) can be found in nearby galaxy clusters. UCDs were recognized as a populous and potentially distinct class of stellar systems about a decade ago. But they are still mysterious objects that are characterized by a compact morphology (30-300 light-years in size) and high masses (more than one million solar masses). More generally, their properties (e.g., their size, shape, or luminosity) are similar to those of both star clusters and dwarf galaxies. Several hundred UCDs have been found to date. Two main formation channels for these puzzling objects have been proposed so far. UCDs might either be very massive star clusters or be ‘normal’ dwarf galaxies transformed by tidal effects.
S. Mieske, M. Hilker, and I. Misgeld (ESO) present a statistical study of the UCD population: they define new statistical tools that relate the number of UCDs to the total luminosity of their host environment. This allows them to use statistical arguments to test the hypothesis that UCDs are bright star clusters. They predict that if UCDs are bright star clusters, we would expect to find only one or two UCDs around the Milky Way, which corresponds to what is seen, as omega Centauri is the only Milky Way satellite that can be considered a UCD.
Full Story: http://www.aanda.org/index.php?option=com_content&task=view&id=788&Itemid=277&lang=en_GB.utf8%2C+en_GB.UT
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