Wednesday, March 17, 2010

Nemesis - Does Our Solar System Have Another Star?

From Astrobiology Magazine:

Summary: Is our Sun part of a binary star system? An unseen companion star, nicknamed “Nemesis,” may be sending comets towards Earth. If Nemesis exists, NASA’s new WISE telescope should be able to spot it.

A dark object may be lurking near our solar system, occasionally kicking comets in our direction.

Nicknamed “Nemesis” or “The Death Star,” this undetected object could be a red or brown dwarf star, or an even darker presence several times the mass of Jupiter.

Why do scientists think something could be hidden beyond the edge of our solar system? Originally, Nemesis was suggested as a way to explain a cycle of mass extinctions on Earth.

The paleontologists David Raup and Jack Sepkoski claim that, over the last 250 million years, life on Earth has faced extinction in a 26-million-year cycle. Astronomers proposed comet impacts as a possible cause for these catastrophes.

Our solar system is surrounded by a vast collection of icy bodies called the Oort Cloud. If our Sun were part of a binary system in which two gravitationally-bound stars orbit a common center of mass, this interaction could disturb the Oort Cloud on a periodic basis, sending comets whizzing towards us.

An asteroid impact is famously responsible for the extinction of the dinosaurs 65 million years ago, but large comet impacts may be equally deadly. A comet may have been the cause of the Tunguska event in Russia in 1908. That explosion had about a thousand times the power of the atomic bomb dropped on Hiroshima, and it flattened an estimated 80 million trees over an 830 square mile area.

While there’s little doubt about the destructive power of cosmic impacts, there is no evidence that comets have periodically caused mass extinctions on our planet. The theory of periodic extinctions itself is still debated, with many insisting that more proof is needed. Even if the scientific consensus is that extinction events don’t occur in a predictable cycle, there are now other reasons to suspect a dark companion to the Sun.

The Footprint of Nemesis

The smaller object in these two photos is a brown dwarf that orbits the star Gliese 229. Located in the constellation Lepus and about 19 light years from Earth, the brown dwarf Gliese 229B is about 20 to 50 times the mass of Jupiter. Image credit: NASA

A recently-discovered dwarf planet, named Sedna, has an extra-long and usual elliptical orbit around the Sun. Sedna is one of the most distant objects yet observed, with an orbit ranging between 76 and 975 AU (where 1 AU is the distance between the Earth and the Sun). Sedna’s orbit is estimated to last between 10.5 to 12 thousand years. Sedna’s discoverer, Mike Brown of Caltech, noted in a Discover magazine article that Sedna’s location doesn’t make sense.

"Sedna shouldn't be there,” said Brown. “There's no way to put Sedna where it is. It never comes close enough to be affected by the Sun, but it never goes far enough away from the Sun to be affected by other stars.”

Perhaps a massive unseen object is responsible for Sedna’s mystifying orbit, its gravitational influence keeping Sedna fixed in that far-distant portion of space.

“My surveys have always looked for objects closer and thus moving faster,” Brown told Astrobiology Magazine. “I would have easily overlooked something so distant and slow moving as Nemesis.”

John Matese, Emeritus Professor of Physics at the University of Louisiana at Lafayette, suspects Nemesis exists for another reason. The comets in the inner solar system seem to mostly come from the same region of the Oort Cloud, and Matese thinks the gravitational influence of a solar companion is disrupting that part of the cloud, scattering comets in its wake. His calculations suggest Nemesis is between 3 to 5 times the mass of Jupiter, rather than the 13 Jupiter masses or greater that some scientists think is a necessary quality of a brown dwarf. Even at this smaller mass, however, many astronomers would still classify it as a low mass star rather than a planet, since the circumstances of birth for stars and planets differ.

The “New Object” labeled in this image is Sedna, a dwarf planet with a 12,000-year orbit around the Sun. It’s a mystery why Sedna has such an elongated orbit.
The Oort Cloud is thought to extend about 1 light year from the Sun. Matese estimates Nemesis is 25,000 AU away (or about one-third of a light year). The next-closest known star to the Sun is Proxima Centauri, located 4.2 light years away.

Richard Muller of the University of California Berkeley first suggested the Nemesis theory, and even wrote a popular science book on the topic. He thinks Nemesis is a red dwarf star 1.5 light years away. Many scientists counter that such a wide orbit is inherently unstable and could not have lasted long – certainly not long enough to have caused the extinctions seen in Earth’s fossil record. But Muller says this instability has resulted in an orbit that has changed greatly over billions of years, and in the next billion years Nemesis will be thrown free of the solar system.

Binary star systems are common in the galaxy. It is estimated that one-third of the stars in the Milky Way are either binary or part of a multiple-star system.

Red dwarfs are also common – in fact, astronomers say they are the most common type of star in the galaxy. Brown dwarfs are also thought to be common, but there are only a few hundred known at this time because they are so difficult to see. Red and brown dwarfs are smaller and cooler than our Sun, and do not shine brightly. If red dwarfs can be compared to the red embers of a dying fire, then brown dwarfs would be the smoldering ash. Because they are so dim, it is plausible that the Sun could have a secret companion even though we’ve searched the sky for many years with a variety of instruments.

NASA’s newest telescope, the Wide-field Infrared Survey Explorer (WISE), may be able to answer the question about Nemesis once and for all.

Finding Dwarfs in the Dark

Illustration of the “Oort Cloud,” a vast region of comets thought to extend a light year beyond our Sun.
Image credit: NASA/JPL/Donald K. Yeoman
WISE looks at our universe in the infrared part of the spectrum. Like the Spitzer space telescope, WISE is hunting for heat. The difference is that WISE has a much wider field of view, and so is able to scan a greater portion of the sky for distant objects.

WISE began scanning the sky on January 14, and NASA recently released the mission’s first images. The mission will map the entire sky until October, when the spacecraft’s coolant runs out.

Part of the WISE mission is to search for brown dwarfs, and NASA expects it could find one thousand of the dim stellar objects within 25 light years of our solar system.

Davy Kirkpatrick at NASA’s Infrared Processing and Analysis Center at Caltech found nothing when he searched for Nemesis using data from the Two Micron All Sky Survey (2MASS). Now Kirkpatrick is part of the WISE science team, ready to search again for any signs of a companion to our Sun.

Kirkpatrick doesn’t think Nemesis will be the red dwarf star with an enormous orbit described by Muller. In his view, Matese’s description of Nemesis as a low mass object closer to home is more plausible.

“I think the possibility that the Sun could harbor a companion of another sort is not a crazy idea,” said Kirkpatrick. “There might be a distant object in a more stable, more circular orbit that has gone unnoticed so far.”

Ned Wright, professor of astronomy and physics at UCLA and the principal investigator for the WISE mission, said that WISE will easily see an object with a mass a few times that of Jupiter and located 25,000 AU away, as suggested by Matese.

Astronomers think there could be as many brown dwarfs as stars like our Sun, but brown dwarfs are often too cool to find using visible light. Using infrared light, the WISE mission could find many brown dwarfs within 25 light years of the Sun. These two pictures show simulated data before and after the WISE mission (stars are not real). The simulated picture on the left shows known stars (white and yellow) and brown dwarfs (red) in our solar neighborhood. The picture on the right shows additional brown dwarfs WISE is expected to find.
Image credit: NASA/JPL-Caltech

“This is because Jupiter is self-luminous like a brown dwarf,” said Wright. “But for planets less massive than Jupiter in the far outer solar system, WISE will be less sensitive.”

Comet “Siding Spring” appears to streak across the sky like a superhero in this new infrared image from NASA's Wide-field Infrared Survey Explorer, or WISE. WISE will be looking for comets and asteroids that might pose a threat to Earth.
Image credit: NASA/JPL-Caltech/UCLA
Neither Kirkpatrick nor Wright think Nemesis is disrupting the Oort cloud and sending comets towards Earth, however. Because they envision a more benign orbit, they prefer the name "Tyche" (the good sister).

Regardless of what they expect to find, the WISE search won’t focus on one particular region of the sky.

“The great thing about WISE, as was also true of 2MASS, is that it's an all-sky survey,” said Kirkpatrick. “There will be some regions such as the Galactic Plane where the observations are less sensitive or fields more crowded, but we'll search those areas too. So we're not preferentially targeting certain directions.”

We may not have an answer to the Nemesis question until mid-2013. WISE needs to scan the sky twice in order to generate the time-lapsed images astronomers use to detect objects in the outer solar system. The change in location of an object between the time of the first scan and the second tells astronomers about the object’s location and orbit. Then comes the long task of analyzing the data.

“I don't suspect we'll have completed the search for candidate objects until mid-2012, and then we may need up to a year of time to complete telescopic follow-up of those objects,” said Kirkpatrick.

Even if Nemesis is not found, the WISE telescope will help shed light on the darkest corners of the solar system. The telescope can be used to search for dwarf planets like Pluto that orbit the Sun off the solar system’s ecliptic plane. The objects that make up the Oort Cloud are too small and far away for WISE to see, but it will be able to track potentially dangerous comets and asteroids closer to home.

Tuesday, March 16, 2010

"Spooky Action At A Distance"

From Belmont Club:

Suppose you could watch something — or someone — by observing its doppelganger. Not the thing in itself, but its shadow. Ridiculous? Maybe not. According to the Guardian Lockheed Martin filed a patent application for a quantum radar system which operates on precisely that principle. The Guardian writes:

In theory entangled particles could be used to reveal details of objects they have never interacted with. If one particle bumped into an aircraft its twin would react in the same way, even if it never left the laboratory. Work out a way to read that behaviour, and an image could be built up, even with no information being directly transmitted from the target.

The patent application itself suggests that by entangling waves of different characteristics the radar can decipher one by observing the other. In this way the frequency which cannot travel far can pass on the information to the frequency which can. It is a kind of information relay race in which the baton started by things which can look through walls, see IEDs emplaced underground and past stealthy coatings can be passed to something which can reach the radar receiver. The saying that you can run but can’t hide may be truer than ever.

The Lockheed Martin patent envisages a different use for entanglement. Current radar systems become less useful as range increases, because the frequencies needed to transmit over long distances are less sensitive. According to the patent this problem can be removed by entangling light at different frequencies and then sending them out together as a bundle.

It says: “Entangled radar waves can combine one or more particles with a relatively high frequency for resolution, with one or more particles at a lower frequency for more effective propagation.” The radar beam could then “propagate through different types of mediums and resolve different types of target”.

Research into quantum entanglement is at the heart of a revolution in understanding just how things happen and while knowledge of that process remains incomplete, developments this area are already changing cryptography, communication and computation. Recently DARPA has solicited research which can show “beyond any doubt that manifestly quantum effects occur in biology, and demonstrate through simulation proof-of concept experiments that devices that exploit these effects could be developed into biomimetic sensors.” Biomimetic sensors are “devices, or systems that imitate nature … of special interest to researchers in nanotechnology, robotics, artificial intelligence (AI), the medical industry, and the military.” What Albert Einstein called “spooky action at a distance” is rapidly becoming part of the technology because it seems to work though don’t quite understand it.

The impact of these new ideas will eventually spread past the hard sciences and technology into our zeitgeist. Popular culture is still largely based on 19th century physical concepts, on the ‘common sense’ of the 1920s. It is bound to be modified by our new knowledge. Sir Arthur Eddington once said that “not only is the universe stranger than we imagine, it is stranger than we can imagine”. That is probably because we only see part of it and are perplexed and surprised when the balance comes into view. And now that 21st century science is bringing more of the strangeness to the surface I think we will find a remarkable willingness in the public to embrace it.

One of my favorite works of fantastic literature is an early 20th century story called The Charwoman’s Shadow, which is all about a young man’s attempts to restore an old woman’s shadow to herself because as it turns out, the least obviously valuable part of us is what is most important. The shadow was entangled with her; and a sorcerer by holding it in his keeping kept her in his thrall. You know, sort of like quantum radar. That today’s public might receive that comparison as more than poetic license stems from its exposure to the information revolution. This is the first generation that understands the value of the invisible, that knows the secret power pattern can impose on the inanimate; which grasps the relationship of software to hardware and who, perhaps for the first time since the electric light dispelled the shadows of night, can sense the ghost in the machine by the full light of day.

Arthur Clarke once wrote that “the only way of discovering the limits of the possible is to venture a little way past them into the impossible,” and that moreover, “any sufficiently advanced technology is indistinguishable from magic.” The magic is back. The hard part is being able to stay on our feet in its midst.

So the 21st century threatens to reverse the tremendous set piece on which the Charwoman’s Shadow ended, with the defeated sorcerer fleeing over the Pyrenees, summoning everything magical in the world after him to hide forever in the Land Beyond the Moon’s Rising. Perhaps for a while, but not for all time. A century which taught that the loss of magic was the price of enlightenment has given way to one in which marvels and perils we thought imaginary now rise before us into dark and wondrous heights and we must nerve ourselves to meet them.

Psychopaths' brains wired to seek rewards, no matter the consequences

From Eurekalert:

The brains of psychopaths appear to be wired to keep seeking a reward at any cost, new research from Vanderbilt University finds. The research uncovers the role of the brain's reward system in psychopathy and opens a new area of study for understanding what drives these individuals.

The results were published March 14, 2010, in Nature Neuroscience.

"Psychopaths are often thought of as cold-blooded criminals who take what they want without thinking about consequences," Joshua Buckholtz, a graduate student in the Department of Psychology and lead author of the new study, said. "We found that a hyper-reactive dopamine reward system may be the foundation for some of the most problematic behaviors associated with psychopathy, such as violent crime, recidivism and substance abuse."

Previous research on psychopathy has focused on what these individuals lack—fear, empathy and interpersonal skills. The new research, however, examines what they have in abundance—impulsivity, heightened attraction to rewards and risk taking. Importantly, it is these latter traits that are most closely linked with the violent and criminal aspects of psychopathy.

"There has been a long tradition of research on psychopathy that has focused on the lack of sensitivity to punishment and a lack of fear, but those traits are not particularly good predictors of violence or criminal behavior," David Zald, associate professor of psychology and of psychiatry and co-author of the study, said. "Our data is suggesting that something might be happening on the other side of things. These individuals appear to have such a strong draw to reward—to the carrot—that it overwhelms the sense of risk or concern about the stick."

To examine the relationship between dopamine and psychopathy, the researchers used positron emission tomography, or PET, imaging of the brain to measure dopamine release, in concert with a functional magnetic imaging, or fMRI, probe of the brain's reward system.

"The really striking thing is with these two very different techniques we saw a very similar pattern—both were heightened in individuals with psychopathic traits," Zald said.

Study volunteers were given a personality test to determine their level of psychopathic traits. These traits exist on a spectrum, with violent criminals falling at the extreme end of the spectrum. However, a normally functioning person can also have the traits, which include manipulativeness, egocentricity, aggression and risk taking.

In the first portion of the experiment, the researchers gave the volunteers a dose of amphetamine, or speed, and then scanned their brains using PET to view dopamine release in response to the stimulant. Substance abuse has been shown in the past to be associated with alterations in dopamine responses. Psychopathy is strongly associated with substance abuse.

"Our hypothesis was that psychopathic traits are also linked to dysfunction in dopamine reward circuitry," Buckholtz said. "Consistent with what we thought, we found people with high levels of psychopathic traits had almost four times the amount of dopamine released in response to amphetamine."

In the second portion of the experiment, the research subjects were told they would receive a monetary reward for completing a simple task. Their brains were scanned with fMRI while they were performing the task. The researchers found in those individuals with elevated psychopathic traits the dopamine reward area of the brain, the nucleus accumbens, was much more active while they were anticipating the monetary reward than in the other volunteers.

"It may be that because of these exaggerated dopamine responses, once they focus on the chance to get a reward, psychopaths are unable to alter their attention until they get what they're after," Buckholtz said. Added Zald, "It's not just that they don't appreciate the potential threat, but that the anticipation or motivation for reward overwhelms those concerns."