Galaxies Are Born Of Violence Between Dark Matter and Interstellar Gas

Source:

http://www.sciencedaily.com/releases/2007/11/071129183827.htm

ScienceDaily (Nov. 30, 2007) — Researchers using supercomputer simulations have exposed a very violent and critical relationship between interstellar gas and dark matter when galaxies are born -- one that has been largely ignored by the current model of how the universe evolved.

The findings, published in Science, solve a longstanding problem of the widely accepted model -- Cold Dark Matter cosmology -- which suggests there is much more dark matter in the central regions of galaxies than actual scientific observations suggest.
"This standard model has been hugely successful on the largest of scales--those above a few million light-years--but suffers from several persistent difficulties in predicting the internal properties of galaxies," says Sergey Mashchenko, research associate in the Department of Physics & Astronomy at McMaster University. "One of the most troublesome issues concerns the mysterious dark matter that dominates the mass of most galaxies."
Supercomputer cosmological simulations prove that indeed, this problem can be resolved. Researchers modeled the formation of a dwarf galaxy to illustrate the very violent processes galaxies suffer at their births, a process in which dense gas clouds in the galaxy form massive stars, which, at the ends of their lives, blow up as supernovae.
"These huge explosions push the interstellar gas clouds back and forth in the centre of the galaxy," says Mashchenko, the lead author of the study. "Our high-resolution model did extremely accurate simulations, showing that this 'sloshing' effect -- similar to water in a bathtub-- kicks most of the dark matter out of the centre of the galaxy."
Cosmologists have largely discounted the role interstellar gas has played in the formation of galaxies and this new research, says Mashchenko, will force scientists to think in new terms and could lead to a better understanding of dark matter.
The simulations reported in the research paper were carried out on the Shared Hierarchical Academic Research Computing Network (SHARCNET).
Adapted from materials provided by McMaster University.

Fausto Intilla

www.oloscience.com

Astronomers Find Stellar Cradle Where Planets Form

Source:

http://www.sciencedaily.com/releases/2007/11/071129141146.htm

ScienceDaily (Nov. 30, 2007) — Astronomers at the University of Illinois have found the first clear evidence for a cradle in space where planets and moons form. The cradle, revealed in photographs taken with NASA’s Spitzer Space Telescope, consists of a flattened envelope of gas and dust surrounding a young protostar.

“We are seeing this object in the early stages of stellar birth,” said U. of I. astronomy professor Leslie Looney, the lead author of a paper accepted for publication in Astrophysical Journal Letters. “Eventually, the protostar will form into a star much like our sun, and the disk will form into planets and moons.”
Located about 800 light-years away in the constellation Cepheus, the object is obscured by dust and therefore invisible to the eye. However, the Spitzer Space Telescope’s sensitive infrared camera can penetrate the dust, and reveal the structures within.
The brightest structure consists of an enormous, almost linear flow of shocked molecular hydrogen gas erupting from the protostar’s two magnetic poles. These bipolar jets are so long, light would take about 1 1/2 years to travel from one end to the other.
In star-formation theory, a cloud of gas and dust collapses to form a star and its planets. As the cloud collapses, it begins to rotate faster and faster, like a pirouetting ice skater pulling in her arms. The force of the growing magnetic field ejects some of the gas and dust along the magnetic axis, forming the bipolar jets seen in the photograph.
“If material was not shed in this fashion, the protostar’s spin would speed up so fast it would break apart,” Looney said.
The planet-forming region is perpendicular to, and roughly centered on the polar jets. There, seen in silhouette against a bright background of galactic infrared emission, is the flattened disk of a circumstellar envelope.
Theorized, but never before seen, the flattened disk is an expected outcome for cloud-collapse theories that include magnetic fields or rotation.
“Some theories had predicted that envelopes flatten as they collapse onto their stars and surrounding planet-forming disks,” Looney said, “but we hadn’t seen any strong evidence of this until now.”
With Looney, co-authors of the paper are former undergraduate student John Tobin (now at the University of Michigan) and graduate student Woojin Kwon.
The Spitzer Space Telescope is operated by the Jet Propulsion Laboratory at the California Institute of Technology. Funding was provided by NASA.
Adapted from materials provided by University of Illinois.

Fausto Intilla

www.oloscience.com

Astronomers Discover Youngest Solar Systems Ever

Source:

http://www.sciencedaily.com/releases/2007/11/071129113705.htm

ScienceDaily (Nov. 29, 2007) — Astronomers at the University of Michigan have found what are believed to be some of the youngest solar systems yet detected.

The systems are around the young stars UX Tau A and LkCa 15, located in the Taurus star formation region just 450 light years away. Using a telescope that measures levels of infrared radiation, the researchers noticed gaps in the protoplanetary disks of gas and dust surrounding these stars. They say those gaps are most likely caused by infant planets sweeping those areas clear of debris.
A paper on the findings by astronomy doctoral student Catherine Espaillat, professor Nuria Calvet, and their colleagues is published in Astrophysical Journal Letters.
"Previously, astronomers were seeing holes at the centers of protoplanetary disks and one of the theories was that the star could be photoevaporating that material," said Espaillat, first author of the paper.
Photoevaporation refers to the process of heating up the dust and gas in the surrounding cloud until it evaporates and dissipates.
"We found that in some stars, including these two, instead of a hole, there's a gap," Espaillat said. "It's more like a lane has been cleared within the disk. That is not consistent with photoevaporation. The existence of planets is the most probable theory that can explain this structure."
The researchers used NASA's Spitzer Space Telescope for this study. The infrared orbiting telescope observes energy at wavelengths invisible to optical telescopes. That allowed astronomers to study these "pre-main sequence stars" in a deeper way.
A main sequence star is an average adult star, like the sun, which burns by converting hydrogen into helium. Pre-main sequence stars like UX Tau A and LkCa 15 haven't yet established this conversion process. They derive energy from gravitational contraction. UX Tau A and LkCa 15 are both about 1 million years old.
"They're baby stars," Calvet said. The sun, for comparison, is a middle-aged star at 4.5 billion years old. Calvet said this research adds new insights to the study of solar systems.
"We are looking for our history," Calvet said. "We are looking for the history of solar systems, trying to understand how they form."
The paper, published December 1, is called "On the Diversity of the Taurus Transitional Disks: UX Tau A & LkCa 15."
Adapted from materials provided by University of Michigan.

Fausto Intilla

www.oloscience.com

Earth-like Lightning On Venus, European Space Probe Confirms

Source:

http://www.sciencedaily.com/releases/2007/11/071128155513.htm

ScienceDaily (Nov. 29, 2007) — Venus is a hellish place of high temperatures and crushing air pressure. The European Space Agency's Venus Express mission adds into this mix the first confirmation that the Venusian atmosphere generates its own lightning.

"In addition to all the pressure and heat, we can confirm there is lightning on Venus -- maybe even more activity than there is here on Earth," said Christopher Russell, a NASA-sponsored scientist on Venus Express from the University of California, Los Angeles, and lead author of one of the Nature papers*. "Not a very good place to vacation, that is for sure."
The discovery puts Venus in elite planetary company. Scientists currently know of only three other planetary bodies in the entire universe that generate lightning -- Earth, Jupiter and Saturn. Lightning on Venus -- as well as on any other planet -- is an important discovery because the electrical discharges drive the chemistry of an atmosphere by breaking molecules into fragments that can then join with other fragments in unexpected ways. The lightning on Venus is unique from that found on Earth, Jupiter and Saturn in that it is the only lightning known that is not associated with water clouds. Instead, on Venus, the lightning is associated with clouds of sulfuric acid.
Any future missions to the second rock from the sun may have to take into account the electrical activity in the Venusian atmosphere.
The confirming measurements of the electrical discharges were made with data obtained by the Venus Express magnetometer instrument provided by the Space Research Institute in Graz, Austria. The measurements were taken once a day for two minutes, during a period when the spacecraft was closest to Venus. A Venusian day is about 117 days long.
With its primary mission completed, Venus Express will now embark upon its extended mission to watch Earth’s nearest planetary neighbor for two more Venusian days. Among other things, it will look for the telltale infrared radiation from lava flows. In 2010, when a Japanese mission, Venus Climate Orbiter, also called Planet-C, arrives at Venus, scientists will be able to compare results from the two spacecraft.
More than 250 scientists and engineers across Europe are involved in the Venus Express mission, supported by their institutes and national space agencies. The mission also sees the contribution of scientists from Russia and Japan, as well as from NASA, which sponsors 15 American Venus Express scientists and provides support to the radio science investigation via its Deep Space Network antennas.
*The discovery is part of the Venus Express science findings that appear in a special section of the Nov. 29 issue of the journal Nature.
Related images and graphics are online at http://www.esa.int/venus .
Adapted from materials provided by NASA/Jet Propulsion Laboratory.

Fausto Intilla

www.oloscience.com

Organic 'Building Blocks' Of Life Discovered In Titan's Atmosphere

Source:

http://www.sciencedaily.com/releases/2007/11/071128151808.htm

ScienceDaily (Nov. 29, 2007) — Scientists analysing data gathered by the Cassini spacecraft have confirmed the presence of heavy negative ions in the upper regions of Titan's atmosphere. These particles may act as organic building blocks for even more complicated molecules and their discovery was completely unexpected because of the chemical composition of the atmosphere (which lacks oxygen and mainly consists of nitrogen and methane). The observation has now been verified on 16 different encounters.

Professor Andrew Coates, researcher at UCL's Mullard Space Science Laboratory and lead author of a new paper*, says: "Cassini's electron spectrometer has enabled us to detect negative ions which have 10,000 times the mass of hydrogen. Additional rings of carbon can build up on these ions, forming molecules called polycyclic aromatic hydrocarbons, which may act as a basis for the earliest forms of life.
"Their existence poses questions about the processes involved in atmospheric chemistry and aerosol formation and we now think it most likely that these negative ions form in the upper atmosphere before moving closer to the surface, where they probably form the mist which shrouds the planet and which has hidden its secrets from us in the past. It was this mist which stopped the Voyager mission from examining Titan more closely in 1980 and was one of the reasons that Cassini was launched."
The new paper builds on work published in Science (May 11) where the team found smaller tholins, up to 8,000 times the mass of hydrogen, forming away from the surface of Titan.
Dr Hunter Waite of the South West Research Institute in Texas and author of the earlier study, said: "Tholins are very large, complex, organic molecules thought to include chemical precursors to life. Understanding how they form could provide valuable insight into the origin of life in the solar system."
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL.
*These findings will be published in Geophysical Research Letters on November 28.
Adapted from materials provided by University College London.

Fausto Intilla

www.oloscience.com

Discovering Teenage Galaxies Billions Of Light Years Away

Source:

http://www.sciencedaily.com/releases/2007/11/071127171056.htm

ScienceDaily (Nov. 28, 2007) — Staring for the equivalent of every night for two weeks at the same little patch of sky with ESO's Very Large Telescope, an international team of astronomers has found the extremely faint light from teenage galaxies billions of light years away. These galaxies, which the research team believes are the building blocks of normal galaxies like our Milky Way, had eluded detection for three decades, despite intensive searches.
The team, led by Martin Haehnelt of the University of Cambridge, UK, Michael Rauch and George Becker of the Observatories of the Carnegie Institution, USA, and Andy Bunker of the Anglo-Australian Observatory, reports their results in the 1 March 2008 issue of the Astrophysical Journal.
"The farther we look back into space the farther we see back in time," explained Rauch." We were actually trying to measure a faint signal from intergalactic gas caused by the cosmic ultraviolet background radiation. But as often happens in science, we got a surprise and found something we weren't looking for--dozens of faint, discrete objects emitting radiation from neutral hydrogen in the so-called Lyman alpha line, a fundamental signature of protogalaxies."
A popular theory of galaxy formation predicts that the gas accreted forming smaller protogalaxies, which then collided and merged to become the massive galaxies seen today. The new discovery lends strong support to this theory.
During the 1990s there was mounting evidence in favor of this hierarchical picture of galactic evolution, including measurements of distant quasars by Rauch and collaborators that showed how the properties of cosmic gas clouds--the reservoir of matter for galaxy formation--fit within that scheme.
"Most of those gas clouds are dark and visible only as foreground objects, which cast something of a shadow against a bright background quasar," Becker said. "Intriguingly, one class of these shadows--known as damped Lyman alpha systems--was suspected to arise when those small, protogalactic building blocks intersect the line-of-sight to the quasar. For many years, these shadows were our only hint that a population of numerous early galaxies existed."
"This is the first time that the sky has been searched to this depth and the unrivalled sensitivity of the picture taken with the VLT was key to succeeding," says Haehnelt.
"Previous attempts have usually been frustrated by the difficulty of detecting extremely faint objects: the amount of time required even with an 8-metre class telescope like the VLT considerably exceeds typical observing time awards. We have thus exploited the periods of less good weather with the FORS2 spectrograph at the VLT, taking advantage of the service observing mode," says Becker.
In service mode, ESO staff astronomers at Paranal are responsible for carrying out the actual observations, taking all the specific requirements into account.
"We were actually trying to measure a faint signal from intergalactic gas caused by the cosmic ultraviolet background radiation. But as often happens in science, we got a surprise and found something we weren't looking for--dozens of faint, discrete objects emitting radiation from neutral hydrogen in the so-called Lyman alpha line, a fundamental signature of protogalaxies," explains Rauch.
The same small patch of sky, centred on a quasar, was observed between 2004 and 2006 for an unprecedented 92 hours, the equivalent of about 12 complete nights, allowing the astronomers to obtain a spectrum of the Universe when it was only 2 billion years old.
The result of this search is the detection of 27 faint objects. The weak light signal that the team has detected from these distant objects implies low star formation rates and a small amount of chemical enrichment, suggesting that they are indeed at an early stage of formation.
"The properties of the emitters seem to provide an excellent match to those of 'Damped Lyman Alpha Systems', the main reservoir of neutral hydrogen in the far Universe," says Andy Bunker. "This suggests that the objects found are the long-sought counterparts of the DLAS in emission. The new observations confirm theoretical research proposing that galaxies like our own have formed by the amalgamation of small proto-galaxies early on in the history of the Universe," he adds.
"What makes our discovery particularly exciting is that it opens the route to find large numbers of building blocks of normal galaxies and that we will now be able to study in detail how galaxies like our Milky Way have come together, " says Martin Haehnelt.
The results are reported in a paper in press in the Astrophysical Journal ("A Population of Faint Extended Line Emitters and the Host Galaxies of Optically Thick QSO Absorption Systems", by M. Rauch et al.). The team is composed of Michael Rauch and George Becker (Observatories of the Carnegie Institution of Washington, Pasadena, USA), Martin Haehnelt (Institute of Astronomy, Cambridge, UK), Andrew Bunker (Anglo-Australian Observatory and School of Physics, Exeter, UK), Francine Marleau (Spitzer Science Center, Caltech, USA), James Graham (University of California, Berkeley, USA), Stefano Cristiani (Osservatorio Astronomico di Trieste, INAF, Italy), Matt J. Jarvis (University of Hertfordshire, UK), Cedric Lacey, Simon Morris, and Tom Theuns (Durham University, UK), Celine Peroux (Observatoire Astronomique de Marseille-Provence, France), and Huub Röttgering (Leiden Observatory, The Netherlands)
Adapted from materials provided by ESO.

Fausto Intilla
www.oloscience.com

Einstein's Biggest Blunder? Dark Energy May Be Consistent With Cosmological Constant

Source:

http://www.sciencedaily.com/releases/2007/11/071127142128.htm

ScienceDaily (Nov. 28, 2007) — Einstein's self-proclaimed "biggest blunder" -- his postulation of a cosmological constant (a force that opposes gravity and keeps the universe from collapsing) -- may not be such a blunder after all, according to the research of an international team of scientists that includes two Texas A&M University researchers.

The team is working on a project called ESSENCE that studies supernovae (exploding stars) to figure out if dark energy -- the accelerating force of the universe -- is consistent with Einstein's cosmological constant.
Texas A&M researchers Nicholas Suntzeff and Kevin Krisciunas are part of the project, which began in October of 2002 and is scheduled to end next month after achieving its goal of discovering and studying 200 supernovae. The team uses a 4-meter diameter telescope in Chile during the observing season of October to December to find the supernovae.
In 1917, Einstein was working on his Theory of General Relativity and was trying to come up with an equation that describes a static universe -- one that stands still and does not collapse under the force of gravity in a big crunch. In order to keep the universe static in his theory, Einstein introduced a cosmological constant -- a force that opposes the force of gravity.
Then, 12 years later, Edwin Hubble discovered that the universe is not static -- it is actually expanding. So Einstein scrapped his idea of a cosmological constant and dismissed it as his biggest blunder.
In 1998, however, two teams of scientists, one of which Texas A&M researcher Suntzeff co-founded, discovered that the universe is not only expanding, but its expansion is actually accelerating -- going faster and faster.
"So there had to be some other force that had overcome the force of gravity and is driving the universe into an exponential acceleration," Suntzeff said. This opposing force is what scientists now call dark energy, and it is believed to constitute roughly 74 percent of the universe. The other constituents of the universe are dark matter, which composes about 22 percent of the universe, and ordinary matter, which is about 4 percent.
"Eighty years later, it turns out that Einstein may have been right [about a cosmological constant]," Krisciunas said. "So he was smarter than he gave himself credit for."
The type of supernovae that the ESSENCE team studies all give off the same amount of energy and have essentially the same peak brightness. Researchers can compare the observed brightness of a supernova that they see in the sky to its known actual brightness to figure out how far away the supernova is.
Researchers also look at what is called the redshift of the supernova, which tells them how fast the universe is expanding. When scientists compare the distance of the supernova to its redshift, they can measure the acceleration of the expansion of the universe. This acceleration is caused by the force scientists call dark energy.
The ESSENCE team can then use the value of the acceleration to figure out the density of dark energy, which they then use to calculate what is called the w-parameter. For Einstein's cosmological constant to be correct, the w-parameter must equal -1, and so far, the results of the ESSENCE project seem to confirm that it is indeed very close to -1.
"The magic value is -1 exactly," Krisciunas said. "If the number turns out to be precisely -1, then this dark energy is a relatively simple thing -- it is Einstein's cosmological constant." The team won't have the final results until later next year, but right now, the measurement is coming in at -1 plus or minus 10 percent error, Suntzeff said, so the initial data seems to point to Einstein being correct.
"We can never test [dark energy] in the laboratory, so astronomers have to measure it [through observational data], and one of the ways we're measuring it is with supernovae in the ESSENCE project," Suntzeff said. "Dark energy is completely unexplained by conventional physics. Perhaps this is a manifestation of the 5th dimension from string theory. Or maybe it is a new vacuum energy density that is changing slowly in time. We have no idea, and that is what excites both physicists and astronomers."
Adapted from materials provided by Texas A&M University.

Fausto Intilla

www.oloscience.com