X-ray Evidence Supports Possible New Class Of Supernova

Recent observations have uncovered evidence that helps to confirm the identification of the remains of one of the earliest stellar explosions recorded by humans.

The new study shows that the supernova remnant RCW 86 is much younger than previously thought. As such, the formation of the remnant appears to coincide with a supernova observed by Chinese astronomers in 185 A.D. The study used data from NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton Observatory.

"There have been previous suggestions that RCW 86 is the remains of the supernova from 185 A.D.," said Jacco Vink of University of Utrecht, the Netherlands, and lead author of the study. "These new X-ray data greatly strengthen the case."

When a massive star runs out of fuel, it collapses on itself, creating a supernova that can outshine an entire galaxy. The intense explosion hurls the outer layers of the star into space and produces powerful shock waves. The remains of the star and the material it encounters are heated to millions of degrees and can emit intense X-ray radiation for thousands of years.

In their stellar forensic work, Vink and colleagues studied the debris in RCW 86 to estimate when its progenitor star originally exploded. They calculated how quickly the shocked, or energized, shell is moving in RCW 86, by studying one part of the remnant. They combined this expansion velocity with the size of the remnant and a basic understanding of how supernovas expand to estimate the age of RCW 86.

"Our new calculations tell us the remnant is about 2,000 years old," said Aya Bamba, a coauthor from the Institute of Physical and Chemical Research (RIKEN), Japan. "Previously astronomers had estimated an age of 10,000 years."

The younger age for RCW 86 may explain an astronomical event observed almost 2000 years ago. In 185 AD, Chinese astronomers (and possibly the Romans) recorded the appearance of a new bright star. The Chinese noted that it sparkled like a star and did not appear to move in the sky, arguing against it being a comet. Also, the observers noticed that the star took about eight months to fade, consistent with modern observations of supernovas.

RCW 86 had previously been suggested as the remnant from the 185 AD event, based on the historical records of the object's position. However, uncertainties about the age provided significant doubt about the association.

"Before this work I had doubts myself about the link, but our study indicates that the age of RCW 86 matches that of the oldest known supernova explosion in recorded history," said Vink. "Astronomers are used to referencing results from 5 or 10 years ago, so it's remarkable that we can build upon work from nearly 2000 years ago."

The smaller age estimate for the remnant follows directly from a higher expansion velocity. By examining the energy distribution of the X-rays, a technique known as spectroscopy, the team found most of the X-ray emission was caused by high-energy electrons moving through a magnetic field. This is a well-known process that normally gives rise to low-energy radio emission. However, only very high shock velocities can accelerate the electrons to such high energies that X-ray radiation is emitted.

"The energies reached in this supernova remnant are extremely high," said Andrei Bykov, another team member from the Ioffe Institute, St. Peterburg, Russia. "In fact, the particle energies are greater than what can be achieved by the most modern particle accelerators."

The difference in age estimates for RCW 86 is due to differences in expansion velocities measured for the supernova remnant. The authors speculate that these variations arise because RCW 86 is expanding into an irregular bubble blown by a wind from the progenitor star before it exploded. In some directions, the shock wave has encountered a dense region outside the bubble and slowed down, whereas in other regions the shock remains inside the bubble and is still moving rapidly. These regions give the most accurate estimate of the age.

Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov.

Space Telescope Seeks Earth-sized Planets

A space telescope designed to seek out planets not much bigger than Earth has been launched into space from a location in Kazakhstan.

The mission is expected to increase knowledge of planets smaller than Saturn, of which only a few are known, Newscientist.com said. The majority of the 200 extra solar planets, about the size of Jupiter, were detected from the ground by scientists observing a tug the planets exert on their parent stars.

The new telescope, called Convection Rotation and Planetary Transits, or COROT, will be able to detect smaller planets, scientists said.

The COROT mission is led by France's National Space Study Center with participation from the European Space Agency. COROT will start its scientific observing around the end of January 2007. The entire mission is scheduled to last 2 1/2 years.

New Way To Form Black Hole Uncovered

Nature has again thrown astronomers for a loop. Just when they thought they understood how gamma-ray bursts formed, they have uncovered what appears to be evidence for a new kind of cosmic explosion. These seem to arise when a newly born black hole swallows most of the matter from its doomed parent star.

Gamma-ray bursts (GRBs), the most powerful explosions in the Universe, signal the formation of a new black hole and come in two flavours, long and short ones. In recent years, international efforts have shown that long gamma-ray bursts are linked with the explosive deaths of massive stars (hypernovae).

Last year, observations by different teams - including the GRACE and MISTICI collaborations that use ESO's telescopes - of the afterglows of two short gamma-ray bursts provided the first conclusive evidence that this class of objects most likely originates from the collision of compact objects: neutron stars or black holes.

The newly found gamma-ray bursts, however, do not fit the picture. They instead seem to share the properties of both the long and short classes.

"Some unknown process must be at play, about which we have presently no clue," said Massimo Della Valle of the Osservatorio Astrofisico di Arcetri in Firenze, Italy, lead author of one of the reports published in this week's issue of the journal Nature. "Either it is a new kind of merger which is able to produce long bursts, or a new kind of stellar explosion in which matter can't escape the black hole."

One of the mysterious events went bang on 14 June 2006, hence its name, GRB 060614. The gamma-ray burst lasted 102 seconds and belongs clearly to the category of long GRBs. As it happened in a relatively close-by galaxy, located only 1.6 billion light-years away in the constellation Indus, astronomers worldwide eagerly pointed their telescopes toward it to capture the supernova, watching and waiting as if for a jack-in-the-box to spring open.

The MISTICI collaboration used ESO's Very Large Telescope to follow the burst for 50 days. "Despite our deep monitoring, no rebrightening due to a supernova was seen," said Gianpiero Tagliaferri from the Observatory of Brera, Italy and member of the team. "If a supernova is present, if should at least be 100 times fainter than any other supernova usually associated with a long burst."

The burst exploded in a dwarf galaxy that shows moderate signs of star formation. Thus young, massive stars are present and, at the end of its life one of them could have uttered this long, agonising cry before vanishing into a black hole. "Why did it do so in a dark way, with no sign of a supernova?" asked Guido Chincarini, from the University of Milano-Bicocca, Italy, also member of the team. "A possibility is that a massive black hole formed that did not allow any matter to escape. All the material that is usually ejected in a supernova explosion would then fall back and be swallowed."

The same conclusion was previously reached by another team, who monitored both GRB 060614 and another burst, GRB 060505 (5 May 2006) for 5 and 12 weeks, respectively. For this, they used the ESO VLT and the 1.54-m Danish telescope at La Silla.

GRB 060505 was a faint burst with a duration of 4 seconds, and as such also belongs to the category of long bursts.

For GRB 060505, the astronomers could only see the burst in visible light for one night and then it faded away, while for GRB 060614, they could only follow it for four nights after the burst. Thus, if supernovae were associated with these long-bursts, as one would have expected, they must have been about a hundred times fainter than a normal supernova.

"Although both bursts are long, the remarkable conclusion from our monitoring is that there were no supernovae associated with them," said Johan Fynbo from the DARK Cosmology Centre at the Niels Bohr Institute of the Copenhagen University in Denmark, who led the study. "It is a bit like not hearing the thunder from a nearby storm when one could see a very long lasting flash."

For the May burst, the team has obtained deep images in very good observing conditions allowing the exact localisation of the burst in its host galaxy. The host galaxy turns out to be a small spiral galaxy, and the burst occurred in a compact star-forming region in one of the spiral arms of the galaxy. This is strong evidence that the star that made the GRB was massive.

"For the 5 May event, we have evidence that it was due to a massive star that died without making a supernova," said Fynbo. "We now have to find out what is the fraction of massive stars that die without us noticing, that is, without producing either a gamma-ray burst or a supernova."

"Whatever the solution to the problem is, it is clear that these new results challenge the commonly accepted scenario, in which long bursts are associated with a bright supernova," said Daniele Malesani, from the International School for Advanced Studies in Trieste, and now also at the DARK Cosmology Centre. "Our hope is to be able to find more of these unconventional bursts. The chase is on!"

Pinpoint Sound Beams Hunt Buried Land Mines

Researchers at MIT's Lincoln Laboratory are developing a highly pinpointed sound beam that can detect buried land mines from a safe distance. The new beam will use sound to seek out land mines like a bat uses sonar to hunt its prey.

The researchers built a prototype detector and tested it at the Cold Regions Research and Engineering Laboratory Army Corps of Engineers land-mine facility in New Hampshire. They were able to detect both metal and plastic mines but said that the system will have to get a major boost in acoustic power before minefield searchers can use it safely.

Robert W. Haupt, a technical staff member at Lincoln Lab, explores innovative ways to find and reduce the large number of land mines abandoned in war-torn countries. An estimated 26,000 people are killed or maimed every year by 60 to 70 million undetected land mines in 70 countries. Those casualties include military troops but most are civilians--half of them children under age 16--who step on uncleared minefields after a war.

Many existing prototype mine detection systems can detect only metal, have limited range or are impractical in the field. "Reliable methods that quickly and accurately locate land mines made of metal and plastic, unexploded ordnance and other mine-like targets are desperately needed," Haupt said.

Haupt and fellow Lincoln Lab staff member Ken Rolt developed a high-powered sound transmitter that looks like a stop sign studded with 35mm film canisters or prescription pill containers. This is called a parametric acoustic array, and Haupt and Rolt have built one of the most powerful ones around.

The array is made up of ceramic transducers--devices that emit a powerful narrow acoustic beam at ultrasonic frequencies. One meter away, the ultrasonic pressure level measures 155 decibels--more acoustic power than a jet engine. Immediately outside the beam, the acoustic intensity dies away to almost nothing.

By a process know as self-demodulation, the air in front of the acoustic beam converts the ultrasound to much lower frequency audible tones that sound like extremely loud tuning forks. Unlike ultrasound, the low-frequency sound can penetrate the ground, causing detectable vibrations in the mine's plungers and membranes.

"The use of ultrasound allows us to make a very narrow and highly directional beam, like a sound flashlight," Haupt said. It would take a huge number of conventional loudspeakers to do the same trick, and they would weigh too much, take up too much space and use too much power to be practical, he said. Plus, they would deafen anyone within earshot. "Using a narrow sound beam, we can put sound just where we want it, and we can minimize sound levels outside the beam to avoid harming the operators or people nearby," he said.

Once the sound beam "hits" buried ordnance, the vibrations from the mine, resonating from the sound waves, push up on the ground and can be measured remotely with a laser system called a Doppler vibrometer. The sound signature of a mine looks like a mountain range of spikes compared with the flat-line response of the rocks and dirt around it.

"It turns out that mines will vibrate quite differently from anything else," Haupt said. "You can determine what types of mines there are--and which countries made them--by their unique signatures."

Haupt also is working with Oral Buyukozturk, professor of civil engineering at MIT, to tailor the system to detect damage in cement bridge piers from as far away as the shore.

Research Yields Optical Buffer Memory

U.S. scientists, using state-of-the-art semiconductor manufacturing technology, said they created an optical buffer memory on a miniature silicon chip.

The device -- a temporary storage area for light signals -- works by slowing down the light signals, said Yurii Vlasov of the IBM Thomas J Watson Research Center, Yorktown Heights, N.Y.

The optical buffer was made by connecting a string of up to 100 tiny silicon ring waveguides -- tiny oval "racetracks" with a perimeter of just 55 micrometers, Vlasov said. By experimenting with various designs, the team created the buffer that could store up to 10 bits of information at data rates of up to 20 gigabits per second, he said.

While silicon ring waveguides were reported before, Vlasov said his team is the first to show it is possible to use a large number of rings to create the device and test its compatibility with real data at gigabit speeds.

Noting further testing is needed, Vlasov said such a buffer could help future optical networks synchronize different data streams without converting the signals into the electronic domain.

His team's findings were published in Nature Photonics.

'Invisible' Transistors Developed

Futuristic "invisible" electronics may appear sooner rather than later, thanks to U.S. researchers developing transparent, high-performance transistors.

The transistors can be assembled inexpensively on glass and plastic, creating high quality displays on car windshields, goggles or billboards, the Northwestern University researchers said.

Developing new types of displays powered by electronics without visible wires has been going on for years. But no one could develop materials for transistors that could both be "invisible" and maintain a high level of performance, the university said in a news release.

"Our development provides new strategies for creating transparent electronics," said Tobin J. Marks, professor of materials science and engineering at Northwestern, who led the research. "You can imagine a variety of applications for new electronics that haven't been possible previously -- imagine displays of text or images that would seem to be floating in space."

To create the transistors, Marks' team combined films of the inorganic semiconductor indium oxide with a layer of self-assembling organic molecules that provides insulation. The films can be fabricated at room temperature, allowing the transistors to be produced at a low cost.

Magnetic Whirlpools Feed Earth's Magnetosphere

Giant whirlpools of electrically charged gas, some 40,000 kilometres across, have been witnessed above the Earth by a team of European and American scientists. Using data from ESA's Cluster quartet of spacecraft, the researchers have shown that these whirlpools inject electrified gas into the magnetic environment of the Earth.

The magnetic field generated inside the Earth protects the planet from the electrically charged particles given out by the Sun. However, it is only a partially effective shield.

In the same way that a car can only travel along roads, electrically charged gas, known as plasma, can only travel along magnetic field lines, never across them. For a car to suddenly change direction, it has to use a road junction.

For a particle of plasma to suddenly jump onto a different field line, there has to be a reconnection event. In a reconnection, magnetic fields lines spontaneously break and then join up with other nearby lines. In doing so, the plasma is suddenly redirected along new routes.

Scientists know this happens in Earth's magnetosphere because of changes to the plasma sheet. This is one of the inner regions of the Earth's magnetic field. Plasma in the sheet is usually hot and tenuous, whereas the solar wind is cooler and denser. At certain times, the sheet fills with cooler and denser plasma over the course of a few hours.

For this to happen, the solar wind plasma must somehow be able to cross the Earth’s magnetic boundary, known as the magnetopause. Yet, until now scientists had no observational evidence that reconnection inside whirlpools contribute to this process. "Wondering how the solar wind could get into the plasma sheet is how I became interested in this problem," says Katariina Nykyri, lead author of the results, from the Imperial College, London, UK.

Together with colleagues, Nykyri began investigating a strange event recorded by Cluster on 3 July 2001. At this time, Cluster was passing the dawn side of the Earth. In this region of space, the solar wind is sliding past the Earth's magnetopause, in roughly the same way as wind blows across the surface of an ocean.

A previous Cluster observation had shown that whirlpools of plasma can be whipped up by this configuration. Such whirlpools are known as Kelvin-Helmholtz instabilities and scientists suspected them of being the location of magnetic reconnection but no one had found any conclusive evidence that this was the case.

Cluster can recognise magnetic reconnection because of what researchers call 'rotational discontinuities'. These show up as sudden changes in the direction of the plasma flow and magnetic field. After a painstaking analysis, Nykyri found just such rotational discontinuities in the data for 3 July 2001. To be certain of her result, she reanalysed the data four times.

Then she developed a computer model to simulate the event. The computer showed that the Cluster data was only understandable if the whirlpools were causing magnetic reconnection to take place. In these reconnections, plasma was being fed down through the magnetic boundary of Earth and into the magnetosphere.

The work does not stop there. Nykyri and colleagues are now developing more sophisticated computer simulations to understand the whirlpools’ three-dimensional behaviour. "This is a very big challenge," she says, because of the additional numerical processes involved.

She also plans to search the Cluster data archive for more examples of these events.