LUX dark matter results confirmed

A new calibration technique fired neutrons directly into the Large Underground Xenon (LUX) dark matter detector, increasing calibration accuracy by a factor of 10. 

Analysis based on the calibration confirms that if "low-mass" dark matter particles had passed through the detector during its initial run, Large Underground Xenon would have seen them. 

Credit: Matt Kapust/Sanford Underground Research Facility

A new high-accuracy calibration of the LUX (Large Underground Xenon) dark matter detector demonstrates the experiment's sensitivity to ultra-low energy events.

The new analysis strongly confirms the result that low-mass dark matter particles were a no-show during the detector's initial run, which concluded last summer.

The first dark matter search results from LUX detector were announced last October.

The detector proved to be exquisitely sensitive, but found no evidence of the dark matter particles during its first 90-day run, ruling out a wide range of possible models for dark matter particles.

Previous experiments had detected potential signatures of dark matter particles with a very low mass, but LUX turned up no such signal.

This latest work was focused on demonstrating the high sensitivity of LUX to potential signals in the search for those low-mass particles.

Rick Gaitskell

"The new calibration improved our calibration accuracy by about a factor of 10," said Rick Gaitskell, professor of physics at Brown University and co-spokesperson for LUX.

"It demonstrates that our first dark matter search result, which showed no sign of low-mass particles, is absolutely robust."

The results of the new analysis were presented Wednesday, Feb. 19, 2014, at the Lake Louise Winter Institute in Alberta, Canada, by James Verbus, a graduate student at Brown who led the new calibration work.

Dark matter is thought to account for about 80 percent of the mass of the universe. Though it has not yet been detected directly, its existence is a near certainty among physicists.

Without the gravitational influence of dark matter, galaxies and galaxy clusters would simply fly apart into the vastness of space.

It's not clear exactly what dark matter is, but the leading idea is that it consists of subatomic particles called weakly interacting massive particles (WIMPs).

WIMPs are thought to be practically ubiquitous in the universe, but because they interact so rarely with other forms of matter, they generally pass right through the earth and everything on it without anyone knowing it.

The LUX is designed to detect those rare occasions when a WIMP does interact with other forms of matter.

The detector consists of a third of a ton of supercooled xenon in a tank festooned with light sensors, each capable of detecting a single photon at a time.

As WIMPs pass through the tank, they should, on very rare occasions, bump into the nucleus of a xenon atom.

Those bumps cause the nucleus to recoil, creating a tiny flash of light and an ion charge, both of which are picked up by LUX sensors.

The detector is more than a mile underground at the Sanford Underground Research Facility in South Dakota, where it is shielded from cosmic rays and radiation that might interfere with a potential dark matter signal.

This latest work was an entirely new way of calibrating the detector to recognize a WIMP signal.

NASA STEREO: Circumsolar dust ring in Venus's orbit confirmed

Venus. Photo courtesy of NASA

A trio of researchers from the Open University and the University of Central Lancashire in the U.K., has confirmed that a ring of dust surrounds the sun in the orbit of Venus.

In their paper published in the journal Science, the team describes how they used data from NASA's twin STEREO probes to confirm the existence of the dust ring.

Scientists have known for many years that a cloud of dust exists throughout the solar system, ranging from the asteroid belt to the sun—it's called the zodiacal cloud and is made of interplanetary dust.

Over the past few decades, space scientists have come to realize that some of that dust can be pulled into the orbit of a planet by that planet's gravity.

The Earth travels through just such a ring—it was discovered approximately 20 years ago.

Twenty years before that, probes sent into space by the Soviet Union sent back evidence suggesting that such a ring existed in Venus's path.

Unfortunately, evidence from those probes wasn't strong enough to actually prove that the ring existed.

In this new effort, the researchers first created a model of what they believed a dust ring in Venus's orbit should look like, then compared it with data from a pair of NASA probes that allow for stereoscopic viewing of portions of space.

That helped them find what they were looking for—evidence of Venus's dust ring but it didn't conform exactly to the model they'd created (because it was partially based on data that describes the dust ring in Earth's orbit).

Instead, they found that Venus's dust ring had two steps—one existed just outside of Venus's orbit, the other just inside of it.

Finding dust rings in the orbits of other planets is not easy—the difference in the density of such a dust cloud and the zodiacal cloud is roughly just 10 percent. Plus it's so large it's difficult to see from our vantage point.

The dust cloud in Venus's orbit, for example, has a diameter of 220 million kilometers.

Another problem is that the individual dust particles don't persist in a ring for very long—as a part of the zodiacal cloud, they are constantly moving slowly towards the sun.

That means that the dust particles that exist in a ring are constantly being replenished.

Scientists believe gaining a better understanding of the dust clouds that exist in planetary orbits can help in studying exoplanets, offering information that may not be available in other ways.

More information: Imaging of a Circumsolar Dust Ring Near the Orbit of Venus, Science 22 November 2013: Vol. 342 no. 6161 pp. 960-963 DOI: 10.1126/science.1243194

Chandra confirm evidence of jet in Milky Way's black hole

Composite image of Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way. 

Credit: X-ray: NASA /CXC /UCLA /Z. Li et al; Radio: NRAO /VLA

Astronomers have long sought strong evidence that Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, is producing a jet of high-energy particles. 

Finally they have found it, in new results from NASA's Chandra X-ray Observatory and the National Science Foundation's Very Large Array (VLA) radio telescope.

Previous studies, using a variety of telescopes, suggested there was a jet, but these reports—including the orientation of the suspected jets—often contradicted each other and were not considered definitive.

"For decades astronomers have looked for a jet associated with the Milky Way's black hole. Our new observations make the strongest case yet for such a jet," said Zhiyuan Li of Nanjing University in China, lead author of a study appearing in an upcoming edition of the Astrophysical Journal and available online now.

Jets of high-energy particles are found throughout the universe, on large and small scales. They are produced by young stars and by black holes a thousand times larger than the Milky Way's black hole.

They play important roles in transporting energy away from the central object and, on a galactic scale, in regulating the rate of formation of new stars.

"We were very eager to find a jet from Sgr A* because it tells us the direction of the black hole's spin axis.

This gives us important clues about the growth history of the black hole," said Mark Morris of the University of California at Los Angeles, a co-author of the study.

The study shows the spin axis of Sgr A* is pointing in one direction, parallel to the rotation axis of the Milky Way, which indicates to astronomers that gas and dust have migrated steadily into Sgr A* over the past 10 billion years.

If the Milky Way had collided with large galaxies in the recent past and their central black holes had merged with Sgr A*, the jet could point in any direction.

The jet appears to be running into gas near Sgr A*, producing X-rays detected by Chandra and radio emission observed by the VLA.

The two key pieces of evidence for the jet are a straight line of X-ray emitting gas that points toward Sgr A* and a shock front—similar to a sonic boom—seen in radio data, where the jet appears to be striking the gas.

Additionally, the energy signature, or spectrum, in X-rays of Sgr A* resembles that of jets coming from supermassive black holes in other galaxies.

Scientists think jets are produced when some material falling toward the black hole is redirected outward. Since Sgr A* is presently known to be consuming very little material, it is not surprising that the jet appears weak.

A jet in the opposite direction is not seen, possibly because of gas or dust blocking the line of sight from Earth or a lack of material to fuel the jet.

The region around Sgr A* is faint, which means the black hole has been quiet in the past few hundred years.

However, a separate Chandra study announced last month shows that it was at least a million times brighter before then.

"We know this giant black hole has been much more active at consuming material in the past. When it stirs again, the jet may brighten dramatically," said co-author Frederick K. Baganoff of the Massachusetts Institute of Technology in Cambridge, Mass.

More information: "Evidence for a Parsec-scale Jet from the Galactic Center Black Hole: Interaction with Local Gas," Zhiyuan Li, Mark R. Morris, and Frederick K. Baganoff. xxx.lanl.gov/abs/1310.0146

NASA Stereo: Phaethon confirmed as rock comet

The Sun-grazing asteroid, Phaethon, has betrayed its true nature by showing a comet-like tail of dust particles blown backwards by radiation pressure from the Sun.

Unlike a comet, however, Phaethon's tail doesn't arise through the vaporization of an icy nucleus.

During its closest approach to the Sun, researchers believe that Phaethon becomes so hot that rocks on the surface crack and crumble to dust under the extreme heat.

David Jewitt

The findings will be presented by David Jewitt on Tuesday 10 September at the European Planetary Science Congress (EPSC) 2013 in London.

Most meteor showers arise when the Earth ploughs through streams of debris released from comets in the inner solar system.

The Geminids, which grace the night sky annually in December, are one of the best known and most spectacular of the dozens of meteor showers.

However, astronomers have known for 30 years that the Geminids are not caused by a comet but by a 5 km diameter asteroid called (3200) Phaethon.

Until recently, though, and much to their puzzlement, astronomer's attempts to catch Phaethon in the act of throwing out particles all ended in failure.

The tide began to turn in 2010 when Jewitt and colleague, Jing Li, found Phaethon to be anomalously bright when closest to the Sun.

The key to success was their use of NASA's STEREO Sun-observing spacecraft. Phaethon at perihelion appears only 8 degrees (16 solar diameters) from the sun, making observations with normal telescopes impossible.

Now, in further STEREO observations from 2009 and 2012, Jewitt, Li and Jessica Agarwal have spotted a comet-like tail extending from Phaethon.

"The tail gives incontrovertible evidence that Phaethon ejects dust," said Jewitt. 'That still leaves the question: why? Comets do it because they contain ice that vaporizes in the heat of the Sun, creating a wind that blows embedded dust particles from the nucleus. Phaethon's closest approach to the Sun is just 14 per cent of the average Earth-Sun distance (1AU). That means that Phaethon will reach temperatures over 700 degrees Celsius – far too hot for ice to survive."

NASA Rover Curiosity: Confirms First Drilled Mars Rock Sample

This image from NASA's Curiosity rover shows the first sample of powdered rock extracted by the rover's drill. 

The image was taken after the sample was transferred from the drill to the rover's scoop. 

In planned subsequent steps, the sample will be sieved, and portions of it delivered to the Chemistry and Mineralogy instrument and the Sample Analysis at Mars instrument. 

The scoop is 1.8 inches (4.5 centimeters) wide. The image was obtained by Curiosity's Mast Camera on Feb. 20, or Sol 193, Curiosity's 193rd Martian day of operations.

Image Credit: NASA/JPL-Caltech/MSSS.

NASA's Mars rover Curiosity has relayed new images that confirm it has successfully obtained the first sample ever collected from the interior of a rock on another planet.

No rover has ever drilled into a rock beyond Earth and collected a sample from its interior. Transfer of the powdered-rock sample into an open scoop was visible for the first time in images received Wednesday at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

"Seeing the powder from the drill in the scoop allows us to verify for the first time the drill collected a sample as it bore into the rock," said JPL's Scott McCloskey, drill systems engineer for Curiosity.

"Many of us have been working toward this day for years. Getting final confirmation of successful drilling is incredibly gratifying. For the sampling team, this is the equivalent of the landing team going crazy after the successful touchdown."

The drill on Curiosity's robotic arm took in the powder as it bored a 2.5-inch (6.4-centimeter) hole into a target on flat Martian bedrock on Feb. 8.

The rover team plans to have Curiosity sieve the sample and deliver portions of it to analytical instruments inside the rover.

The scoop now holding the precious sample is part of Curiosity's Collection and Handling for In-Situ Martian Rock Analysis (CHIMRA) device.

During the next steps of processing, the powder will be enclosed inside CHIMRA and shaken once or twice over a sieve that screens out particles larger than 0.006 inch (150 microns) across.

Small portions of the sieved sample later will be delivered through inlet ports on top of the rover deck into the Chemistry and Mineralogy (CheMin) instrument and Sample Analysis at Mars (SAM) instrument.