Tuesday, 16 November 2010

Johnald's Fantastical Daily Link Splurge

Johnald's Fantastical Daily Link Splurge

The Universe’s Most Extreme Black Holes

Posted: 15 Nov 2010 04:03 PM PST

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Black holes, the great gravitational beasts left behind when stars collapse in a supernova, are some of the weirdest and most exotic objects in the universe. But even among these bizarre beasts, some black holes are weirder than others. The youngest black hole ever observed -- just 31 years old -- was announced today, but it's just the latest in a long line of black hole superlatives.


The 31-year-old remains of supernova SN 1979c make up the youngest known black hole.

This supernova in the galaxy M100 approximately 50 million light-years from Earth, was discovered by an amateur astronomer in 1979. The star that exploded that year was just on the edge of the theoretical mass limit for forming black holes, about 20 times the mass of the sun. After the supernova, the leftover matter could either have collapsed into a black hole or an extremely dense neutron star.

New observations from the Chandra X-ray Observatory seem to clinch it in favor of the black hole, astronomers announced today. As material falls in to a black hole, it heats up to millions of degrees and spews X-rays. If the object that was SN 1979c was a neutron star, the brightness of the X-rays it emits would tail off with time. But if it was a black hole, the X-rays would stay nearly as bright as the black hole gobbled new material.

Observations show that SN1979c blasted out X-rays at a constant brightness level between 1995 and 2007, definitely tilting the odds in favor of a black hole -- although the object could still be a rapidly spinning neutron star with a powerful wind of high energy particles.

Image: X-ray: NASA/CXC/SAO/D.Patnaude et al, Optical: ESO/VLT, Infrared: NASA/JPL/Caltech

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Gene Sleuthing Fingers HIV-Spreading Criminals

Posted: 15 Nov 2010 02:26 PM PST

The genetic analyses used to convict two HIV-positive men with knowingly and intentionally infecting 12 women with the virus were published today.

The cases received national attention, and the resulting convictions ultimately rested on multiple streams of evidence. But fundamental to the case against them were phylogenetic maps tracing paths from dozens of infections back to them.

Used in trial and released November 15 in the Proceedings of the National Academy of Sciences, the maps are relevant not only as tools of criminal justice, but demonstrations of the extraordinary detail made possible by genetic analysis.

"Until this finding, you could make statements about which viruses were more closely related to one another, but you didn't know the direction of transmission" when comparing viral samples, said geneticist Michael Metzker of the Baylor College of Medicine. "You could only go so far in describing transmission dynamics. We went one step further in proposing the index case."


The gene-crunching tools used by Metzker's team were relatively old-fashioned, and the scientists had performed similar analyses before, in the case of another intentional HIV transmission. But in that study, they knew who the samples came from, raising questions about whether they already knew what to look for.

In the new study, the researchers did not know the identity of HIV samples from Anthony Whitfield of Olympia, Washington or Philippe Padieu of Collin County, Texas. Neither did they know which samples came from six women who in 2004 charged Whitfield with intentionally infecting them with HIV, nor from six women who in 2009 charged Padieu with the same crime.

Metzker's team compared relationships between the different HIV strains, each of which was subtly different because the virus mutates so rapidly that it can change between transmission events. Despite the changes, the viruses pointed back to common sources.

Metzker's team is far from the first to perform phylogenetic analyses, but rarely is the data so complete. According to Metzker, similar approaches will be useful in many fields.

"It's not restricted to HIV. It could be used in the identification of food-borne diseases where identifying the source of contamination could be very important," he said. "It could be used in identifying sources of biological weapons, if you're trying to pinpoint where an outbreak is taking place. It has lots of applications beyond HIV cases."

Image: Phylogenetic trees of HIV infections traced to their original source./PNAS.

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Citation: "Source identification in two criminal cases using phylogenetic analysis of HIV-1 DNA sequences." By Diane I. Scaduto, Jeremy M. Brown, Wade C. Haaland, Derrick J. Zwickl, David M. Hillis, and Michael L. Metzker. Proceedings of the National Academy of Sciences, Vol. 107 No. 46, November 16, 2010.

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Reader Photos: Jupiter’s Stripe Returns

Posted: 15 Nov 2010 11:11 AM PST

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Jupiter's famous ruddy-orange cloud belt disappeared late last year, hidden under a layer of white ammonia-ice-crystal clouds.

But photos from amateur astrophotographers over the past few days have shown the stripe making a comeback. A small white plume marks where dark clouds are beginning to bubble back to the surface, and it's getting bigger and darker every day. See the progression of the spot in the following slides as, Jupiter puts its belt back on.


Nov. 3: Jon Kristoffersen took these images of Jupiter from Crete, Greece, about a week before the stripe began to return. Jupiter dances with two of its moons, Io (left) and Europa.

Images: Jon Kristoffersen. Animation: Emil Kraaikamp

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Retinal Implant Restores Vision in Blind Mice

Posted: 15 Nov 2010 08:36 AM PST

SAN DIEGO — A new type of prosthetic eye may someday allow blind people to seamlessly see the broad sweep of an ocean or the dimples in a baby's face. The approach, presented Nov. 13 at the Society for Neuroscience's annual meeting, may benefit the estimated 25 million people worldwide who have lost sight due to retinal diseases.

"This is a spectacular example of what we all hoped to be able to do," said Jonathan Victor, a computational-systems neuroscientist who was not involved in the new work. "It's a solution to an abstract problem" that could be useful in many kinds of systems.

Sheila Nirenberg and Chethan Pandarinath, both of Weill Medical College of Cornell University in New York City, tested their new retinal prosthetic in blind mice and found that it allowed the mice to see a baby's face.

Current prosthetics are limited to reproducing simple features, such as bright spots or edges, but miss much of a scene. Many scientists are intent on boosting the retinal prosthetics' power, so that the message from the artificial eye to the brain is stronger. But Nirenberg's work suggests that a second, underappreciated area is also important: the pattern of cell activity in the retina, something she called "a big problem lurking in the background."


Normally, cells that respond to light, called photoreceptors, pick up signals and transfer that information to ganglion cells. These cells then create a complex code for each visual signal that goes into the brain, where the scene is reconstructed. Spotting a dog creates a particular code, for example, different from the code for a teacup or a baby's face. When a retina is degenerated, these photoreceptor cells die and there is no message to send.

Nirenberg's new system mimics the complex behavior of the frontline photoreceptor cells, creating a more natural artificial message for the ganglion cells to interpret. Other prosthetics produce simpler, less recognizable codes, Nirenberg said. These simplified patterns aren't what the brain is used to receiving, so while they can reproduce simple features, they can't reproduce natural scenes. Because the new prosthetic speaks the language that the ganglion cells are accustomed to, the ganglion output — and the image — is more accurate.

"If you want to really restore normal vision, you have to know the retina's code," Nirenberg said. "Once you have that, the door is open to the possibility of restoring normal vision."

To test its prosthetic system, the team decoded the output of the ganglion cells by measuring cellular activity when an image of a baby's face was presented to the retinas of blind mice. Patterns measured from the mice with the new prosthetic reproduced a baby's face in much finer detail than the standard method did. Instead of the standard method's highly pixelized, blurry version of the face, the new prosthetic captured a smooth, clear view of the baby's quizzical expression. "Not only can you tell it's a baby's face, you can tell it's this baby's face," Nirenberg said.

The researchers are currently testing the prosthetic on primates and plan eventually to provide the technology to human patients. That would probably require gene therapy.

"Obviously it's not in humans yet," said Victor, also of Weill Medical College. "Everyone else is working on putting the signal into humans, and now they have the signal to put in. It's extremely exciting."

Image: A new retinal prosthetic creates an image (middle) that more-accurately reconstructs a baby's face (left) than the standard approach (right)./S. Nirenberg

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