SCIENCE NEWS Rachel Courtney & James Ni | ICTP Compilers & Researchers Exotic matter: A closer look at the perfect fluid sheds light on what happened microseconds after the big bang Date: October 2, 2014 Source: DOE/Lawrence Berkeley National Laboratory Summary: By combining data from two high-energy accelerators, nuclear scientists have refined the measurement of a remarkable property of exotic matter known as quark-gluon plasma. The findings reveal new aspects of the ultra-hot, perfect fluid that give clues to the state of the young universe just microseconds after the Big Bang. By combining data from two high-energy accelerators, nuclear scientists have refined the measurement of a remarkable property of exotic matter known as quark-gluon plasma. The findings reveal new aspects of the ultra-hot, perfect fluid that give clues to the state of the young universe just microseconds after the big bang. The multi-institutional team known as the JET Collaboration, led by researchers at the U.S. Department of Energys Lawrence Berkeley National Lab (Berkeley Lab), published their results in a recent issue of Physical Review C. The JET Collaboration is one of the Topical Collaborations in nuclear theory established by the DOE Office of Science in 2010. JET, which stands for the Quantitative Jet and Electromagnetic Tomography, aims to study the probes being used to investigate high-energy, heavy-ion collisions. The Collaboration currently has 12 participating institutions with Berkeley Lab as the leading institute. We have made, by far, the most precise extraction to date of a key property of the quark-gluon plasma, which reveals the microscopic structure of this almost perfect liquid, says Xin-Nian Wang, physicist in the Nuclear Science Division at Berkeley Lab and managing principal investigator of the JET Collaboration. Perfect liquids, Wang explains, have the lowest viscosity-to-density ratio allowed by quantum mechanics, which means they essentially flow without friction. To create and study the quark-gluon plasma, nuclear scientists used particle accelerators called the Relativistic Heavy-ion Collider (RHIC) at the Brookhaven National Laboratory in New York and the Large Hadron Collider (LHC) at CERN in Switzerland. By accelerating heavy atomic nuclei to high energies and blasting them into each other, scientists are able to recreate the hot temperature conditions of the early universe. Inside protons and neutrons that make up the colliding atomic nuclei are elementary particles called quarks, which are bound together tightly by other elementary particles called gluons. Only under extreme conditions, such as collisions in which temperatures exceed by a million times those at the center of the sun, do quarks and gluons pull apart to become the ultra-hot, frictionless perfect fluid known as quark-gluon plasma. The temperature is so high that the boundaries between different nuclei disappear so everything becomes a hot-plasma soup of quarks and gluons, says Wang. This ultra-hot soup is contained within a chamber in the particle accelerator, but it is short-lived -- quickly cooling and expanding -- making it a challenge to measure. Experimentalists have developed sophisticated tools to overcome the challenge, but translating experimental observations into precise quantitative understanding of the quark-gluon plasma has been difficult to achieve until now, he says. In this new work, Wangs team refined a probe that makes use of a phenomenon researchers at Berkeley Lab first theoretically outlined 20 years ago: energy loss of a high-energy particle, called a jet, inside the quark gluon plasma. When a hot quark-gluon plasma is generated, sometimes you also produce these very energetic particles with an energy a thousand times larger than that of the rest of the matter, says Wang. This jet propagates through the plasma, scatters, and loses energy on its way out. Since the researchers know the energy of the jet when it is produced, and can measure its energy coming out, they can calculate its energy loss, which provides clues to the density of the plasma and the strength of its interaction with the jet. Its like an x-ray going through a body so you can see inside, says Wang. One difficulty in using a jet as an x-ray of the quark-gluon plasma is the fact that a quark-gluon plasma is a rapidly expanding ball of fire -- it doesnt sit still. You create this hot fireball that expands very fast as it cools down quickly to ordinary matter, Wang says. So its important to develop a model to accurately describe the expansion of plasma, he says. The model must rely on a branch of theory called relativistic hydrodynamics in which the motion of fluids is described by equations from Einsteins theory of special relativity. Over the past few years, researchers from the JET Collaboration have developed such a model that can describe the process of expansion and the observed phenomena of an ultra-hot perfect fluid. This allows us to understand how a jet propagates through this dynamic fireball, says Wang. Employing this model for the quark-gluon plasma expansion and jet propagation, the researchers analyzed combined data from the PHENIX and STAR experiments at RHIC and the ALICE and CMS experiments at LHC since each accelerator created quark-gluon plasma at different initial temperatures. The team determined one particular property of the quark-gluon plasma, called the jet transport coefficient, which characterizes the strength of interaction between the jet and the ultra-hot matter. The determined values of the jet transport coefficient can help to shed light on why the ultra-hot matter is the most ideal liquid the universe has ever seen, Wang says. Peter Jacobs, head of the experimental group at Berkeley Lab that carried out the first jet and flow measurements with the STAR Collaboration at RHIC, says the new result is very valuable as a window into the precise nature of the quark gluon plasma. The approach taken by the JET Collaboration to achieve it, by combining efforts of several groups of theorists and experimentalists, shows how to make other precise measurements of properties of the quark gluon plasma in the future. The teams next steps are to analyze future data at lower RHIC energies and higher LHC energies to see how these temperatures might affect the plasmas behavior, especially near the phase transition between ordinary matter and the exotic matter of the quark-gluon plasma. This work was supported by the DOE Office of Science, Office of Nuclear Physics and used the facilities of the National Energy Research Scientific Computing Center (NERSC) located at Berkeley Lab. ________________________________________ Story Source: The above story is based on materials provided by DOE/Lawrence Berkeley National Laboratory. ________________________________________ Journal Reference: 1. Karen M. Burke, Alessandro Buzzatti, Ningbo Chang, Charles Gale, Miklos Gyulassy, Ulrich Heinz, Sangyong Jeon, Abhijit Majumder, Berndt Müller, Guang-You Qin, Björn Schenke, Chun Shen, Xin-Nian Wang, Jiechen Xu, Clint Young, Hanzhong Zhang. Extracting the jet transport coefficient from jet quenching in high-energy heavy-ion collisions. Physical Review C, 2014; 90 (1) DOI: 10.1103/PhysRevC.90.014909 Clear skies on exo-neptune: smallest exoplanet ever found to have water vapour Date: September 24, 2014 Source: ESA/Hubble Information Centre Summary: Astronomers have discovered clear skies and steamy water vapor on a planet outside our Solar System. The planet, known as HAT-P-11b, is about the size of Neptune, making it the smallest exoplanet ever on which water vapour has been detected. Astronomers using data from the NASA/ESA Hubble Space Telescope, the Spitzer Space Telescope, and the Kepler Space Telescope have discovered clear skies and steamy water vapour on a planet outside our Solar System. The planet, known as HAT-P-11b, is about the size of Neptune, making it the smallest exoplanet ever on which water vapour has been detected. The results will appear in the online version of the journal Nature on 24 September 2014. The discovery is a milestone on the road to eventually finding molecules in the atmospheres of smaller, rocky planets more akin to Earth. Clouds in the atmospheres of planets can block the view of what lies beneath them. The molecular makeup of these lower regions can reveal important information about the composition and history of a planet. Finding clear skies on a Neptune-size planet is a good sign that some smaller planets might also have similarly good visibility. When astronomers go observing at night with telescopes, they say clear skies to mean good luck, said Jonathan Fraine of the University of Maryland, USA, lead author of the study. In this case, we found clear skies on a distant planet. Thats lucky for us because it means clouds didnt block our view of water molecules. HAT-P-11b is a so-called exo-Neptune -- a Neptune-sized planet that orbits another star. It is located 120 light-years away in the constellation of Cygnus (The Swan). Unlike Neptune, this planet orbits closer to its star, making one lap roughly every five days. It is a warm world thought to have a rocky core, a mantle of fluid and ice, and a thick gaseous atmosphere. Not much else was known about the composition of the planet, or other exo-Neptunes like it, until now. Part of the challenge in analysing the atmospheres of planets like this is their size. Larger Jupiter-like planets are easier to observe and researchers have already been able to detect water vapour in the atmospheres of some of these giant planets. Smaller planets are more difficult to probe -- and all the smaller ones observed to date have appeared to be cloudy. The team used Hubbles Wide Field Camera 3 and a technique called transmission spectroscopy, in which a planet is observed as it crosses in front of its parent star. Starlight filters through the rim of the planets atmosphere and into the telescope. If molecules like water vapour are present, they absorb some of the starlight, leaving distinct signatures in the light that reaches our telescopes. We set out to look at the atmosphere of HAT-P-11b without knowing if its weather would be cloudy or not, said Nikku Madhusudhan, from the University of Cambridge, UK, part of the study team. By using transmission spectroscopy, we could use Hubble to detect water vapour in the planet. This told us that the planet didnt have thick clouds blocking the view and is a very hopeful sign that we can find and analyse more cloudless, smaller, planets in the future. It is groundbreaking! Before the team could celebrate they had to be sure that the water vapour was from the planet and not from cool starspots -- freckles on the face of stars -- on the parent star. Luckily, Kepler had been observing the patch of sky in which HAT-P-11b happens to lie for years. Those visible-light data were combined with targeted infrared Spitzer observations. By comparing the datasets the astronomers could confirm that the starspots were too hot to contain any water vapour, and so the vapour detected must belong to the planet. The results from all three telescopes demonstrate that HAT-P-11b is blanketed in water vapour, hydrogen gas, and other yet-to-be-identified molecules. So in fact it is not only the smallest planet to have water vapour found in its atmosphere but is also the smallest planet for which molecules of any kind have been directly detected using spectroscopy.* Theorists will be drawing up new models to explain the planets makeup and origins. Although HAT-P-11b is dubbed as an exo-Neptune it is actually quite unlike any planet in our Solar System. It is thought that exo-Neptunes may have diverse compositions that reflect their formation histories. New findings such as this can help astronomers to piece together a theory for the origin of these distant worlds. We are working our way down the line, from hot Jupiters to exo-Neptunes, said Drake Deming, a co-author of the study also from University of Maryland, USA. We want to expand our knowledge to a diverse range of exoplanets. The astronomers plan to examine more exo-Neptunes in the future, and hope to apply the same method to smaller super-Earths -- massive, rocky cousins to our home world with up to ten times the mass of Earth. Our Solar System does not contain a super-Earth, but other telescopes are finding them around other stars in droves and the NASA/ESA James Webb Space Telescope, scheduled to launch in 2018, will search super-Earths for signs of water vapour and other molecules. However, finding signs of oceans and potentially habitable worlds is likely a way off. This work is important for future studies of super-Earths and even smaller planets. It could allow astronomers to pick out in advance the planets with atmospheres clear enough for molecules to be detected. Once again, astronomers will be crossing their fingers for clear skies. Notes * Molecular hydrogen has been inferred to exist in many planets, including planets smaller than HAT-P-11b, but no molecule has actually been detected, using spectroscopy, in a planet this small, until now. ________________________________________ Story Source: The above story is based on materials provided by ESA/Hubble Information Centre. ________________________________________ Journal Reference: 1. Jonathan Fraine, Drake Deming, Bjorn Benneke, Heather Knutson, Andrés Jordán et al. Water vapour absorption in the clear atmosphere of a Neptune-sized exoplanet. Nature, Sept 24, 2014 [link] Smallest known galaxy with a supermassive black hole Date: September 17, 2014 Source: University of Utah Summary: Astronomers have discovered that an ultracompact dwarf galaxy harbours a supermassive black hole – the smallest galaxy known to contain such a massive light-sucking object. The finding suggests huge black holes may be more common than previously believed. A University of Utah astronomer and his colleagues discovered that an ultracompact dwarf galaxy harbours a supermassive black hole -- the smallest galaxy known to contain such a massive light-sucking object. The finding suggests huge black holes may be more common than previously believed. It is the smallest and lightest object that we know of that has a supermassive black hole, says Anil Seth, lead author of an international study of the dwarf galaxy published in Thursdays issue of the journal Nature. Its also one of the most black hole-dominated galaxies known. The astronomers used the Gemini North 8-metre optical-and-infrared telescope on Hawaiis Mauna Kea and photos taken by the Hubble Space Telescope to discover that a small galaxy named M60-UCD1 has a black hole with a mass equal to 21 million suns. Their finding suggests plenty of other ultracompact dwarf galaxies likely also contain supermassive black holes -- and those dwarfs may be the stripped remnants of larger galaxies that were torn apart during collisions with yet other galaxies. We dont know of any other way you could make a black hole so big in an object this small, says Seth, an assistant professor of physics and astronomy at the University of Utah. There are a lot of similar ultracompact dwarf galaxies, and together they may contain as many supermassive black holes as there are at the centres of normal galaxies. Black holes are collapsed stars and collections of stars with such strong gravity that even light is pulled into them, although material around them sometimes can spew jets of X-rays and other forms of radiation. Supermassive black holes -- those with the mass of at least 1 million stars like our sun -- are thought to be at the centres of many galaxies. The central, supermassive black hole at the centre of our Milky Way galaxy has the mass of 4 million suns, but as heavy as that is, it is less than 0.01 percent of the galaxys total mass, estimated at some 50 billion solar masses. By comparison, the supermassive black hole at the centre of ultracompact dwarf galaxy M60-UCD1 is five times larger than the Milky Ways, with a mass of 21 million suns, and is a stunning 15 percent of the small galaxys total mass of 140 million suns. That is pretty amazing, given that the Milky Way is 500 times larger and more than 1,000 times heavier than the dwarf galaxy M60-UCD1, Seth says. We believe this once was a very big galaxy with maybe 10 billion stars in it, but then it passed very close to the centre of an even larger galaxy, M60, and in that process all the stars and dark matter in the outer part of the galaxy got torn away and became part of M60, he says. That was maybe as much as 10 billion years ago. We dont know. Seth says ultracompact dwarf galaxy M60-UCD1 may be doomed, although he cannot say when because the dwarf galaxys orbit around M60 isnt known. M60 is among the largest galaxies in what astronomers refer to as the local universe. Eventually, this thing may merge with the center of M60, which has a monster black hole in it, with 4.5 billion solar masses -- more than 1,000 times bigger than the supermassive black hole in our galaxy. When that happens, the black hole we found in M60-UCD1 will merge with that monster black hole. Galaxy M60 also is pulling in another galaxy, named NGC4647. M60 is about 25 times more massive than NGC4647. The study -- conducted by Seth and 13 other astronomers -- was funded by the National Science Foundation in the U.S., the German Research Foundation and the Gemini Observatory partnership, which includes the NSF and scientific agencies in Canada, Chile, Australia, Brazil and Argentina. Ultracompact dwarf galaxies are among the densest star systems in the universe. M60-UCD1 is the most massive of these systems now known, with a total of 140 million solar masses. These dwarf galaxies are less than a few hundred light years across (about 1,700 trillion miles wide), compared with our Milky Ways 100,000-light-year diameter. M60-UCD1 is roughly 54 million light years from Earth or about 320 billion billion miles. But the dwarf galaxy is only 22,000 light years from the center of galaxy M60, which is closer than the sun is to the centre of the Milky Way, Seth says. Astronomers have debated whether these dwarf galaxies are the stripped centers or nuclei of larger galaxies that were ripped away during collisions with other galaxies, or whether they formed like globular clusters -- groups of perhaps 100,000 stars, all born together. There are about 200 globular clusters in our Milky Way, and some galaxies have thousands, Seth says. The astronomers estimated the mass of the dwarf galaxys supermassive black hole by using the Gemini North telescope to measure the speed and motion of stars in orbit around it, and they showed the galaxy contains more mass than would be expected by the amount of starlight it emits. The stars at the centre of M60-UCD1 move at about 230,000 mph -- faster than stars would be expected to move without the black hole. An alternate theory is that M60-UCD1 doesnt have a supermassive black hole, but instead is populated by a lot of massive, dim stars. But Seth says the research teams observations with the Gemini North telescope and analysis of archival photos by the Hubble Space Telescope revealed that mass was concentrated in the galaxys centre, indicating the presence of a supermassive black hole. That suggests that M60-UCD1 is the stripped nucleus of what once was a much larger galaxy, and that other ultracompact dwarf galaxies also may harbor huge black holes, Seth says. The galaxy that was stripped and left M60-UCD1 as a remnant was about 10 billion solar masses, or about one-fifth the mass of the Milky Way, Seth says. The astronomers studied M60-UCD1 because they had published a paper last year showing the galaxy was an X-ray source and was extremely dense. The X-ray emissions suggest gas is being sucked into the black hole at a rate typical of supermassive black holes in much larger galaxies. A video simulation of galaxy M60s gravity stripping M60-UCD1s outer parts is here: vimeo/105370891U ____________________________________ Story Source: The above story is based on materials provided by University of Utah. ________________________________________ Journal Reference: 1. Anil C. Seth, Remco van den Bosch, Steffen Mieske, Holger Baumgardt, Mark den Brok, Jay Strader, Nadine Neumayer, Igor Chilingarian, Michael Hilker, Richard McDermid, Lee Spitler, Jean Brodie, Matthias J. Frank, Jonelle L. Walsh. A supermassive black hole in an ultra-compact dwarf galaxy. Nature, 2014; 513 (7518): 398 DOI: 10.1038/nature13762
Posted on: Tue, 07 Oct 2014 10:22:41 +0000