- Dark Matter Guides Growth of Supermassive Black Holes
- New Horizons Spacecraft Spots Nix and Hydra
- Try Before You Fly: Polish Human Centrifuge
- UK Takes Next Step in Dealing with Major Space Weather Events
- The Strange Case of a Missing Dwarf
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Posted: 19 Feb 2015 02:23 AM PST
Every massive galaxy has a black hole at its center, and the heftier the galaxy, the bigger its black hole. But why are the two related? After all, the black hole is millions of times smaller and less massive than its home galaxy. A new study of football-shaped collections of stars called elliptical galaxies provides new insights into the connection between a galaxy and its black hole. It finds that the invisible hand of dark matter somehow influences black hole growth. "There seems to be a mysterious link between the amount of dark matter a galaxy holds and the size of its central black hole, even though the two operate on vastly different scales," says lead author Akos Bogdan of the Harvard-Smithsonian Center for Astrophysics (CfA).
This new research was designed to address a controversy in the field. Previous observations had found a relationship between the mass of the central black hole and the total mass of stars in elliptical galaxies. However, more recent studies have suggested a tight correlation between the masses of the black hole and the galaxy's dark matter halo. It wasn't clear which relationship dominated. In our universe, dark matter outweighs normal matter - the everyday stuff we see all around us - by a factor of 6 to 1. We know dark matter exists only from its gravitational effects. It holds together galaxies and galaxy clusters. Every galaxy is surrounded by a halo of dark matter that weighs as much as a trillion suns and extends for hundreds of thousands of light-years. To investigate the link between dark matter halos and supermassive black holes, Bogdan and his colleague Andy Goulding (Princeton University) studied more than 3,000 elliptical galaxies. They used star motions as a tracer to weigh the galaxies' central black holes. X-ray measurements of hot gas surrounding the galaxies helped weigh the dark matter halo, because the more dark matter a galaxy has, the more hot gas it can hold onto. They found a distinct relationship between the mass of the dark matter halo and the black hole mass - a relationship stronger than that between a black hole and the galaxy's stars alone. This connection is likely to be related to how elliptical galaxies grow. An elliptical galaxy is formed when smaller galaxies merge, their stars and dark matter mingling and mixing together. Because the dark matter outweighs everything else, it molds the newly formed elliptical galaxy and guides the growth of the central black hole. "In effect, the act of merging creates a gravitational blueprint that the galaxy, the stars and the black hole will follow in order to build themselves," explains Bogdan. The paper describing this work has been accepted for publication in the Astrophysical Journal. This result relied on data from the Sloan Digital Sky Survey and the ROSAT X-ray satellite's all-sky survey. Credit: cfa.harvard.edu  | ||
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Posted: 19 Feb 2015 01:18 AM PST
 85 years after Clyde Tombaugh’s historic discovery of Pluto, the NASA spacecraft set to encounter the icy planet this summer is providing its first views of the small moons orbiting Pluto. The moons Nix and Hydra are visible in a series of images taken by the New Horizons spacecraft from Jan. 27-Feb. 8, at distances ranging from about 125 million to 115 million miles (201 million to 186 million kilometers). The long-exposure images offer New Horizons’ best view yet of these two small moons circling Pluto, which Tombaugh discovered at Lowell Observatory in Flagstaff, Arizona, on Feb. 18, 1930. “Professor Tombaugh’s discovery of Pluto was far ahead its time, heralding the discovery of the Kuiper Belt and a new class of planet,” says Alan Stern, New Horizons principal investigator from Southwest Research Institute, Boulder, Colorado. “The New Horizons team salutes his historic accomplishment.”
Assembled into a seven-frame movie, the new images provide the spacecraft’s first extended look at Hydra (identified by a yellow diamond) and its first-ever view of Nix (orange diamond). The right-hand image set has been specially processed to make the small moons easier to see.
“It’s thrilling to watch the details of the Pluto system emerge as we close the distance to the spacecraft’s July 14 encounter,” says New Horizons science team member John Spencer, also from Southwest Research Institute. “This first good view of Nix and Hydra marks another major milestone, and a perfect way to celebrate the anniversary of Pluto’s discovery.” These are the first of a series of long-exposure images that will continue through early March, with the purpose of refining the team’s knowledge of the moons’ orbits. Each frame is a combination of five 10-second images, taken with New Horizons’ Long-Range Reconnaissance Imager (LORRI) using a special mode that combines pixels to increase sensitivity at the expense of resolution. At left, Nix and Hydra are just visible against the glare of Pluto and its large moon Charon, and the dense field of background stars. The bright and dark streak extending to the right of Pluto is an artifact of the camera electronics, resulting from the overexposure of Pluto and Charon. As can be seen in the movie, the spacecraft and camera were rotated in some of the images to change the direction of this streak, in order to prevent it from obscuring the two moons.
The right-hand images have been processed to remove most of Pluto and Charon’s glare, and most of the background stars. The processing leaves blotchy and streaky artifacts in the images, as well as a few other residual bright spots that are not real features, but makes Nix and Hydra much easier to see. Celestial north is inclined 28 degrees clockwise from the “up” direction in these images. Nix and Hydra were discovered by New Horizons team members in Hubble Space Telescope images taken in 2005. Hydra, Pluto’s outermost known moon, orbits Pluto every 38 days at a distance of approximately 40,200 miles (64,700 kilometers), while Nix orbits every 25 days at a distance of 30,260 miles (48,700 kilometers). Each moon is probably between 25-95 miles (approximately 40- 150 kilometers) in diameter, but scientists won’t know their sizes more precisely until New Horizons obtains close-up pictures of both of them in July. Pluto’s two other small moons, Styx and Kerberos, are still smaller and too faint to be seen by New Horizons at its current range to Pluto; they will become visible in the months to come. The Johns Hopkins University Applied Physics Laboratory manages the New Horizons mission for NASA's Science Mission Directorate in Washington. Alan Stern, of the Southwest Research Institute (SwRI), headquartered in San Antonio, is the principal investigator and leads the mission. SwRI leads the science team, payload operations, and encounter science planning. New Horizons is part of the New Frontiers Program managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. APL designed, built and operates the spacecraft. Credit: pluto.jhuapl.edu  | ||
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Posted: 18 Feb 2015 01:44 PM PST
How do you prepare for the unique experience of weightlessness on a parabolic aircraft flight? An ESA-led team took a ride on this human centrifuge at Poland’s Military Institute of Aviation Medicine. The quartet, including ESA mechatronics engineer Kjetil Wormnes, plan to test a deployable net for the capture of derelict satellites. The centrifuge training on 27–28 January prepared them for this week’s flight on a Falcon 20 from the National Research Council of Canada. “The idea was to acclimatise us to the gravity shifting we’ll experience, to help us anticipate and hopefully avoid any motion sickness,” explains Kjetil.
“This is done to reduce the risk of any problems affecting the experiment. Compared to the Novespace Airbus A300 that ESA normally uses for its parabolic flights, this is a smaller aircraft with no room for extra helpers, so we want everyone to be fit to ensure everything runs smoothly. An indisposed crewmember could be catastrophic.”
Of course, a centrifuge is not the same as a zero-g flight. For example, zero acceleration is only along a single axis and the spin is an additional source of motion sickness.
This Polish centrifuge is rare in that it has an active gondola which can rotate independently. This enables the creation of not only positive g-forces, but also negative (by tipping it upside down) or zero.
Inside there is a full F16 cockipit and flight simulator for training pilots from all over Europe. But the test team experienced a simple programmed acceleration cycle simulating the full set of 25 aircraft parabolas.
“The transitions between the different phases, and in particular from 0 to 2 g was the worst part,” Kjetil reports. “This was the time when the boogie flipped upside down while the centrifuge was still rotating.
“The other bad time was just as the centrifuge braked to stop. For the rest, it was no problem, so long as I didn’t move my head.”
Kjetil was joined by team members from Italy’s STAM company and Poland’s OptiNav and SKA Polska companies, working on a net design being considered for inclusion in ESA’s eDeorbit mission, designed to capture and deorbit large items of space debris as part of the Agency’s Clean Space initiative.
Credit: ESA
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Posted: 18 Feb 2015 12:18 PM PST
A new report published this week lets the British public have a voice in deciding what the next steps should be in preparing the UK to deal with major space weather events such as solar storms. Space weather has the potential to have a massive negative impact on both Earth and space based systems that we take for granted, such as communications networks. This new report, based on contributions from over 1,000 members of the public, scientific and government experts and from a series of public dialogue events, offers some key recommendations on best practice actions to deal with the impact of such events in the future.
Key recommendations from the report include:
Professor Mike Hapgood, Head of Space Weather at STFC RAL Space, highlighted the importance of the project "We welcomed the opportunity to explore how the public feel about the risk from space weather, how we as scientists can explain the real risk and overcome the exaggeration sometimes seen in media stories, and ultimately what we are all prepared to do to reduce the risk".
The significance of this hazard has been emphasised by the inclusion of severe space weather in the UK National Risk Register (NRR) since 2012.
UK's important national infrastructure has become highly dependent on the communications, navigation, timing, meteorological and other services that are provided by space-based systems. If solar storms were to disrupt these satellite systems for an extended period, then many services that we currently take for granted would be affected. Major solar storms also have the potential to directly affect infrastructure on the Earth itself. Crucial capabilities, such as the power distribution network, could be put at risk by the large induced currents that solar storms can create.
Mark Gibbs, Head of Space Weather at the Met Office said: "Space weather can impact the performance of electricity grids, satellites, GPS systems and aviation which, in turn, can impact us all. This project is helping us to understand how best to communicate this to the public so they get the best and most timely advice and warning of space weather impacts."
The report was supported by the Department for Business, Innovation & Skills (BIS) and the results of this project will be used to inform future Government policy.
Space weather studies how solar activity impacts human activities, for example causing disruption to positioning and communications services and to spacecraft operations.
The overall purpose of the space weather public dialogue was to inform the policy of government departments, government agencies and companies in respect of space weather and the consequences on people and infrastructure.
In order to achieve this, the project was designed to gauge public understanding of: space weather; its impacts and scenarios for resilience (both civil society and individuals); and the roles and responsibilities of the Government, companies, communities and individuals in responding to space weather impacts.
The report is published on behalf of a number of major organisations including Sciencewise, the Science and Technology Facilities Council RAL Space team, the Natural Environment Research council (NERC), National Grid and Lloyd’s of London.
The dialogue brought together expertise from the following organisations: Met Office, National Grid, UK Space Agency, British Geological Survey, Staffordshire Civil Contingencies, Reading University, Lancaster University, Cabinet Office, Royal Astronomical Society and GO Science.
Credit: stfc.ac.uk
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Posted: 18 Feb 2015 10:46 AM PST
The new SPHERE instrument on ESO’s Very Large Telescope has been used to search for a brown dwarf expected to be orbiting the unusual double star V471 Tauri. SPHERE has given astronomers the best look so far at the surroundings of this intriguing object and they found — nothing. The surprising absence of this confidently predicted brown dwarf means that the conventional explanation for the odd behaviour of V471 Tauri is wrong. This unexpected result is described in the first science paper based on observations from SPHERE. “The most likely reason is that the brown dwarf does not exist. People thought for many years it must be there, because this system displays an odd behavior - it is a binary which displays eclipses every 12 hours, and these eclipses should be very regular. However, there is a periodic change in the eclipse time we measure from earth,” Adam Hardy of the Universidad Valparaíso in Chile, who led the study, told astrowatch.net.
“The most common explanation for this has been that a brown dwarf orbiting the binary periodically pushes and pulls the stars nearer and farther from earth. The light will then take more or less time to reach the earth, and result in this periodic variation. It is a nice and simple explanation for this phenomena, but it has never been confirmed, so it could easily be that the brown dwarf does not exist, and another effect is causing the periodic change in the eclipse arrival times,” Hardy added.
Some pairs of stars consist of two normal stars with slightly different masses. When the star of slightly higher mass ages and expands to become a red giant, material is transferred to other star and ends up surrounding both stars in a huge gaseous envelope. When this cloud disperses the two move closer together and form a very tight pair with one white dwarf, and one more normal star.
One such stellar pair is called V471 Tauri. It is a member of the Hyades star cluster in the constellation of Taurus and is estimated to be around 600 million years old and about 163 light-years from Earth. The two stars are very close and orbit each other every 12 hours. Twice per orbit one star passes in front of the other — which leads to regular changes in the brightness of the pair observed from Earth as they eclipse each other.
A team of astronomers led by Hardy first used the ULTRACAM system on ESO’s New Technology Telescope to measure these brightness changes very precisely. The times of the eclipses were measured with an accuracy of better than two seconds — a big improvement on earlier measurements.
The eclipse timings were not regular, but could be explained well by assuming that there was a brown dwarf orbiting both stars whose gravitational pull was disturbing the orbits of the stars. They also found hints that there might be a second small companion object.
Up to now however, it has been impossible to actually image a faint brown dwarf so close to much brighter stars. But the power of the newly installed SPHERE instrument on ESO’s Very Large Telescope allowed the team to look for the first time exactly where the brown dwarf companion was expected to be. But they saw nothing, even though the very high quality images from SPHERE should have easily revealed it.
The SPHERE images are so accurate that they would have been able to reveal a companion such as a brown dwarf that is 70 000 times fainter than the central star, and only 0.26 arcseconds away from it. The expected brown dwarf companion in this case was predicted to be much brighter.
“There are many papers suggesting the existence of such circumbinary objects, but the results here provide damaging evidence against this hypothesis,” remarked Hardy.
If there is no orbiting object then what is causing the odd changes to the orbit of the binary? Several theories have been proposed, and, while some of these have already been ruled out, it is possible that the effects are caused by magnetic field variations in the larger of the two stars, somewhat similar to the smaller changes seen in the Sun. This effect is called the Applegate mechanism and results in regular changes in the shape of the star, which can lead to changes in the apparent brightness of the double star seen from Earth.
“A study such as this has been necessary for many years, but has only become possible with the advent of powerful new instruments such as SPHERE. This is how science works: observations with new technology can either confirm, or as in this case disprove, earlier ideas. This is an excellent way to start the observational life of this amazing instrument,” Hardy concluded.
Credit: ESO
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