How Often Do Giant Black Holes Become Hyperactive?

A new study from NASA's Chandra X-ray Observatory tells scientists how often the biggest black holes have been active over the last few billion years. This discovery clarifies how supermassive black holes grow and could have implications for how the giant black hole at the center of the Milky Way will behave in the future.

Most galaxies, including our own, are thought to contain supermassive black holes at their centers, with masses ranging from millions to billions of times the mass of the Sun. For reasons not entirely understood, astronomers have found that these black holes exhibit a wide variety of activity levels: from dormant to just lethargic to practically hyper.

The most lively supermassive black holes produce what are called "active galactic nuclei," or AGN, by pulling in large quantities of gas. This gas is heated as it falls in and glows brightly in X-ray light.

"We've found that only about one percent of galaxies with masses similar to the Milky Way contain supermassive black holes in their most active phase," said Daryl Haggard of the University of Washington in Seattle, WA, and Northwestern University in Evanston, IL, who led the study. "Trying to figure out how many of these black holes are active at any time is important for understanding how black holes grow within galaxies and how this growth is affected by their environment."

This study involves a survey called the Chandra Multiwavelength Project, or ChaMP, which covers 30 square degrees on the sky, the largest sky area of any Chandra survey to date. Combining Chandra's X-ray images with optical images from the Sloan Digital Sky Survey, about 100,000 galaxies were analyzed. Out of those, about 1,600 were X-ray bright, signaling possible AGN activity.

Only galaxies out to 1.6 billion light years from Earth could be meaningfully compared to the Milky Way, although galaxies as far away as 6.3 billion light years were also studied. Primarily isolated or "field" galaxies were included, not galaxies in clusters or groups.

"This is the first direct determination of the fraction of field galaxies in the local Universe that contain active supermassive black holes," said co-author Paul Green of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. "We want to know how often these giant black holes flare up, since that's when they go through a major growth spurt."

A key goal of astronomers is to understand how AGN activity has affected the growth of galaxies. A striking correlation between the mass of the giant black holes and the mass of the central regions of their host galaxy suggests that the growth of supermassive black holes and their host galaxies are strongly linked. Determining the AGN fraction in the local Universe is crucial for helping to model this parallel growth.

One result from this study is that the fraction of galaxies containing AGN depends on the mass of the galaxy. The most massive galaxies are the most likely to host AGN, whereas galaxies that are only about a tenth as massive as the Milky Way have about a ten times smaller chance of containing an AGN.

Another result is that a gradual decrease in the AGN fraction is seen with cosmic time since the Big Bang, confirming work done by others. This implies that either the fuel supply or the fueling mechanism for the black holes is changing with time.

The study also has important implications for understanding how the neighborhoods of galaxies affects the growth of their black holes, because the AGN fraction for field galaxies was found to be indistinguishable from that for galaxies in dense clusters.

"It seems that really active black holes are rare but not antisocial," said Haggard. "This has been a surprise to some, but might provide important clues about how the environment affects black hole growth."

It is possible that the AGN fraction has been evolving with cosmic time in both clusters and in the field, but at different rates. If the AGN fraction in clusters started out higher than for field galaxies -- as some results have hinted -- but then decreased more rapidly, at some point the cluster fraction would be about equal to the field fraction. This may explain what is being seen in the local Universe.

The Milky Way contains a supermassive black hole known as Sagittarius A* (Sgr A*, for short). Even though astronomers have witnessed some activity from Sgr A* using Chandra and other telescopes over the years, it has been at a very low level. If the Milky Way follows the trends seen in the ChaMP survey, Sgr A* should be about a billion times brighter in X-rays for roughly 1% of the remaining lifetime of the Sun. Such activity is likely to have been much more common in the distant past.

If Sgr A* did become an AGN it wouldn't be a threat to life here on Earth, but it would give a spectacular show at X-ray and radio wavelengths. However, any planets that are much closer to the center of the Galaxy, or directly in the line of fire, would receive large and potentially damaging amounts of radiation.

Source: Reprinted news release via Chandra X-ray Center

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Doctors Use Sick Boy's DNA In Diagnosis, Treatment

Doctors and scientists in Wisconsin have published the first detailed account of a groundbreaking medical case in which they sequenced all the genes of a very sick young boy from Monona, Wis., and used the information to treat the child. -- Read the rest on Phyorg

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Electronic Nose Detects Cancer

György Horvath from the University of Gothenburg, Sweden, and researchers from the University of Gävle and KTH Royal Institute of Technology have been able to confirm in tests that ovarian cancer tissue and healthy tissue smell different. The results were published recently in the journal Future Oncology. In a previous project György Horvath used specially trained dogs to demonstrate that ovarian cancers emit a specific scent. The dogs were able to use this scent to distinguish between ovarian cancer tissue and both normal healthy abdominal tissue and other gynaecological cancers. The discovery that the blood of patients with ovarian cancer also has this same specific scent was published in the journal BMC Cancer.

Together with professor Thomas Lindblad from KTH and researcher Jose Chilo from Gävle University, Horvath has worked on detecting this scent using an existing electronic nose at KTH.

"We've managed to detect and register the scent from a form of ovarian cancer, and the scent from a healthy Fallopian tube and healthy womb muscle," says Horvath. "This technical confirmation of a cancer scent will have major practical implications – a sufficiently sensitive and specific method could save hundreds of lives a year in Sweden alone."

A more sensitive electronic scent detector that was recently tested. The basic structure is the same as with existing electronic noses, but they have added several new components to increase its sensitivity.

"Our goal is to be able to screen blood samples from apparently healthy women and so detect ovarian cancer at an early stage when it can still be cured," says Horvath.

Source: Reprinted news release via University of Gothenburg

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World's Largest Neutrino Observatory Completed At South Pole

IceCube Lab SP, Antarctica. Credit: NSF/F. Descamps

 

Culminating a decade of planning, innovation and testing, construction of the world's largest neutrino observatory was successfully completed today.

The final string of optical sensors was installed on Saturday, Dec. 18, in the IceCube Neutrino Observatory, a massive ice-bound telescope that fills a cubic kilometer of deep Antarctic ice. The main IceCube detector now contains 5,160 optical sensors on 86 strings embedded two kilometers below the National Science Foundation's Amundsen-Scott South Pole Station.

The construction, coordinated by the University of Wisconsin-Madison and underway since 2005, was completed on schedule and within budget.

For IceCube principal investigator and UW-Madison physics professor Francis Halzen, the completion of the detector is the realization of a longtime vision.

"Since the 1970s we have dreamed of building a detector of this size, and we have spent 20 years working toward IceCube," explains Halzen. "If the science to come brings half the excitement of completing this instrument, we have a bright future ahead."

From its vantage point at the end of the world, IceCube provides an innovative means to investigate the properties of fundamental particles that originate in some of the most spectacular phenomena in the universe. Its sophisticated optical sensors, frozen into some of the purest ice on Earth, record the rare collisions between the water molecules of the ice and neutrinos - tiny, nearly massless sub-atomic particles that pass undetected through most matter.

Some neutrinos come from the sun, while others come from cosmic rays interacting with the Earth's atmosphere, and dramatic astronomical sources such as exploding stars in the Milky Way and distant galaxies. Ever since neutrinos were discovered in 1956, scientists have hoped to decipher the information these astronomical messengers carry about distant cosmic events.

As the lead institution on the project, UW-Madison coordinated the work needed to design and build the complex and often unique components and software for the massive telescope.

"I have had the great fortune to watch the IceCube project develop over the years from idea to implementation. Completing a project of this scope is a tribute to the creativity and determination of our faculty, researchers, staff, and students," says Martin Cadwallader, UW-Madison vice chancellor for research and dean of the Graduate School. "And of course, this is really just the beginning for IceCube. It will be exciting to watch the discoveries that emerge under continued UW leadership."

The university also designed and built the Enhanced Hot Water Drill, which was assembled at the Physical Sciences Laboratory in Stoughton, Wis. The 4.8-megawatt hot-water drill is a unique machine capable of penetrating more than two kilometers into the ice in less than two days. Once each hole was drilled at the pole, deployment specialists attached optical sensors to cable strings and lowered them to depths between 1,450 and 2,450 meters. Sixty sensors line each of the 86 strings, with four more in surface tanks near each string that comprise the IceTop component of the observatory.

The largest part of the IceCube detector is the ice itself. At these depths, it is dark and optically ultratransparent, allowing the sensors to record the traces of particles from tiny flashes of blue light - called Cherenkov radiation - emitted after a high-energy neutrino strikes one of the water atoms in the ice.

Building IceCube in one of the most remote locations on Earth has come with a special set of challenges. All project personnel, equipment, food, and detector components had to be transported to Antarctica, then flown in ski-equipped C-130 cargo aircraft from McMurdo Station near the Antarctic coast to the South Pole, more than 800 air miles away.

Working only during the relatively warm and short Antarctic summer-from November through February, when the sun shines 24 hours a day-drill and deployment teams worked in round-the-clock shifts to maximize their short time on the ice each year.

The successful completion of the observatory is a milestone for international scientific cooperation on the southernmost continent. In addition to researchers at universities and research labs in the U.S., Belgium, Germany, and Sweden, the countries that funded the observatory, IceCube data are analyzed by the larger IceCube Collaboration, which includes researchers from Barbados, Canada, Japan, New Zealand, Switzerland, and the United Kingdom.

"IceCube is not only a magnificent observatory for fundamental astrophysical research, it is the kind of ambitious science that can only be attempted through the cooperation-the science diplomacy, if you will-of many nations working together in the finest traditions of Antarctic science toward a single goal," says Karl A. Erb, director of NSF's Office of Polar Programs.

Unlike other large-scale science projects, IceCube began collecting data while construction was still underway and has been recording particle events since early 2005. Each year as the detector grew, more and higher quality data made its way from the South Pole to UW-Madison and around the world.

"Even in this challenging phase of the project, we published results on the search for dark matter and found an intriguing patterns in the arrival directions of cosmic rays," says Halzen. "With the completion of IceCube, we are on our way to reaching a level of sensitivity that may allow us to see neutrinos from sources beyond the sun."

Source: Reprinted news release via University of Wisconsin-Madison

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This Robonova Humanoid robot is a natural at the piano. He was taught by Drexel University Music Entertainment Technology Lab student, Alyssa Batula. Watch as he elegantly displays his musical talent with a performance of Twinkle Twinkle Little Star.




Don't you find this extremely adorable?

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Is Santa Going To Be Replaced By Robots?

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Is Santa really going to be replaced by robots? Hey, it could happen but probably won't. I think the old man deserves to retire.

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Meteorite Just One Piece Of An Unknown Celestial Body

Scientists from all over the world are taking a second, more expansive, look at the car-sized asteroid that exploded over Sudan's Nubian Desert in 2008. Initial research was focused on classifying the meteorite fragments that were collected two to five months after they were strewn across the desert and tracked by NASA's Near Earth Object astronomical network. Now in a series of 20 papers for a special double issue of the journal Meteoritics and Planetary Science, published on December 15, researchers have expanded their work to demonstrate the diversity of these fragments, with major implications for the meteorite's origin.

In the first round of research, Carnegie Geophysical scientist Doug Rumble, in collaboration with Muawia Shaddad of the University of Khartoum, examined one fragment of the asteroid, called 2008 TC3, and determined that it fell into a very rare category of meteorite called ureilites. Ureilites have a very different composition from most other meteorites. It has been suggested that all members of this meteoric family might have originated from the same source, called the ureilite parent body, which could have been a proto-planet.

Now Rumble has expanded his work to examine 11 meteorite fragments, focusing on the presence of oxygen isotopes. Isotopes are atoms of the same element that have extra neutrons in their nuclei.

Rumble explains: "Oxygen isotopes can be used to identify the meteorite's parent body and determine whether all the fragments indeed came from the same source. Each parent body of meteorites in the Solar System, including the Moon, Mars, and the large asteroid Vesta, has a distinctive signature of oxygen isotopes that can be recognized even when other factors, such as chemical composition and type of rock, are different."

Rumble and his team prepped tiny crumbs of these 11 meteorite fragments and loaded them into a reaction chamber where they were heated with a laser and underwent chemical reactions to release oxygen and then used another device, called a mass spectrometer, to measure the concentrations of these oxygen isotopes. Results showed that the full range of oxygen isotopes known to be present in ureilites were also present in the studied fragments.

"It was already known that the fragments in the Nubian Desert came from the same asteroid. Taking that into account, these new results demonstrate that the asteroid's source, the ureilite parent body, also had a diversity of oxygen isotopes," says Rumble.

The diversity of oxygen isotopes found in ureilites probably arises from the circumstances of the parent this body's formation. Rumble theorizes that the rock components of this parent body were heated to the point of melting and then cooled into crystals so quickly that the oxygen isotopes present could not come to an equilibrium distribution throughout.

Together the collection of 20 papers published in Meteoritics and Planetary Science offer enormous insight about the formation and composition of ureilites and their hypothesized parent body.

Source: Reprinted press release via Carnegie Institution

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