Universe Today

Image credit: NRAO

Before this week, “Complex H” was thought to be a strange cloud of stars with an unusual trajectory near the Milky Way. But as it turns out, this object is actually a companion galaxy crashing into the outer reaches of our own galaxy in exactly the opposite direction of the Milky Way’s rotation. New observations from the National Science Foundation’s Robert C. Byrd Green Bank Telescope (the world’s largest steerable radio telescope) have placed the object at 108,000 light years from the Milky Way’s centre.

New observations with National Science Foundation’s Robert C. Byrd Green Bank Telescope (GBT) suggest that what was once believed to be an intergalactic cloud of unknown distance and significance, is actually a previously unrecognized satellite galaxy of the Milky Way orbiting backward around the Galactic center.

Jay Lockman of the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, discovered that this object, known as “Complex H,” is crashing through the outermost parts of the Milky Way from an inclined, retrograde orbit. Lockman’s findings will be published in the July 1 issue of the Astrophysical Journal, Letters.

“Many astronomers assumed that Complex H was probably a distant neighbor of the Milky Way with some unusual velocity that defied explanation,” said Lockman. “Since its motion appeared completely unrelated to Galactic rotation, astronomers simply lumped it in with other high velocity clouds that had strange and unpredictable trajectories.”

High velocity clouds are essentially what their name implies, fast-moving clouds of predominately neutral atomic hydrogen. They are often found at great distances from the disk of the Milky Way, and may be left over material from the formation of our Galaxy and other galaxies in our Local Group. Over time, these objects can become incorporated into larger galaxies, just as small asteroids left over from the formation of the solar system sometimes collide with the Earth.

Earlier studies of Complex H were hindered because the cloud currently is passing almost exactly behind the outer disk of the Galaxy. The intervening dust and gas that reside within the sweeping spiral arms of the Milky Way block any visible light from this object from reaching the Earth. Radio waves, however, which have a much longer wavelength than visible light, are able to pass through the intervening dust and gas.

The extreme sensitivity of the recently commissioned GBT allowed Lockman to clearly map the structure of Complex H, revealing a dense core moving on an orbit at a 45-degree angle to the plane of the Milky Way. Additionally, the scientist detected a more diffuse region surrounding the central core. This comparatively rarefied region looks like a tail that is trailing behind the central mass, and is being decelerated by its interaction with the Milky Way.

“The GBT was able to show that this object had a diffuse ‘tail’ trailing behind, with properties quite different from its main body,” said Lockman. “The new data are consistent with a model in which this object is a satellite of the Milky Way in an inclined, retrograde orbit, whose outermost layers are currently being stripped away in its encounter with the Galaxy.”

These results place Complex H in a small club of Galactic satellites whose orbits do not follow the rotation of the rest of the Milky Way. Among the most prominent of these objects are the Magellanic Clouds, which also are being affected by their interaction with the Milky Way, and are shedding their gas in a long stream.

Since large galaxies, like the Milky Way, form by devouring smaller galaxies, clusters of stars, and massive clouds of hydrogen, it is not unusual for objects to be pulled into orbit around the Galaxy from directions other than that of Galactic rotation.

“Astronomers have seen evidence that this accreting material can come in from wild orbits,” said Butler Burton, an astronomer with the NRAO in Charlottesville, Virginia. “The Magellanic clouds are being torn apart from their interaction with the Milky Way, and there are globular clusters rotating the wrong way. There is evidence that stuff was going every-which-way at the beginning of the Galaxy, and Complex H is probably left over from that chaotic period.”

The new observations place Complex H at approximately 108,000 light-years from the Galactic center, and indicate that it is nearly 33,000 light-years across, containing approximately 6 million solar masses of hydrogen.

Radio telescopes, like the GBT, are able to observe these cold, dark clouds of hydrogen because of the natural electromagnetic radiation emitted by neutral atomic hydrogen at radio wavelengths (21 centimeters).

Globular clusters, and certain other objects in the extended Galactic halo, can be studied with optical telescopes because the material in them has collapsed to form hot, bright stars.

The GBT is the world’s largest fully steerable radio telescope. It was commissioned in August of 2000, and continues to be outfitted with the sensitive receivers and components that will allow it to make observations at much higher frequencies.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Original Source: NRAO News Release

Image credit: SOHO

The ESA’s SOHO spacecraft has uncovered new details about the Sun’s solar wind which might overturn previously held theories about exactly how the wind is generated. Astronomers believed that the fast wind emanates from gaps between giant plumes found near the Sun’s polar regions. But the new theory, supported by data from SOHO is that it’s the plumes themselves which are hurling the particles of the fast wind into space. If this controversial theory turns out to be correct, it will clear up a big misunderstanding about the Sun.

We have known for 40 years that space weather affects the Earth, which is buffeted by a ‘wind’ from the Sun, but only now are we learning more about its precise origins. Solving the mystery of the solar wind has been a prime task for ESA’s SOHO spacecraft. Its latest findings, announced on 20 May 2003, may overturn previous ideas about the origin of the ‘fast’ solar wind, which occurs in most of the space around the Sun.

Earlier results from SOHO established that the gas of the fast wind leaks through magnetic barriers near the Sun’s visible surface. Straight, spoke-like features called plumes have also been seen rising from the solar atmosphere at the polar regions, where much of the fast wind comes from. According to previous ideas, the gas of the fast wind streams out in the gaps between the plumes.

“Not so,” says Alan Gabriel of the Institut d’Astrophysique Spatiale near Paris, France. Careful observations with SOHO now suggest that most of the fast wind leaves the Sun via the plumes themselves, which are denser than their surroundings. Gabriel and his team tracked gas rising at about 60 kilometres per second to a height of 250 000 kilometres above the Sun’s visible surface.

“If this controversial result is right, it will clear up a big misunderstanding,” says Bernhard Fleck, ESA’s Project Scientist for SOHO. “We need to know how the fast wind is subsequently accelerated to 750 kilometres per second. To find out, we’d better be looking in the right places.”

SOHO has also investigated the origin of a slower wind, half the speed of the fast wind, which comes from the Sun’s equatorial regions. The gas of the ‘slow’ wind leaks from triangular features called ‘helmets’, which are plainly protruding into the Sun’s atmosphere during a solar eclipse. Blasts of gas called ‘coronal mass ejections’ also contribute to the solar wind in the equatorial zone of the Sun.

The ESA/NASA Ulysses spacecraft has twice passed over the poles of the Sun and signalled the relative importance of these fast and slow winds. Its measurements show that the fast wind predominates in the heliosphere, which is a huge bubble blown into interstellar space by the Sun’s outpourings, and extending far beyond the outermost planets. In interplanetary space, the fast wind often collides with the slow wind. Like the mass ejections, the collisions create shock waves that agitate the Earth’s space environment.

The four satellites of ESA’s Cluster mission are now studying the interaction between the solar wind and our planet’s defences. The Earth’s magnetic field creates a bubble within the heliosphere, but it does not give us perfect protection from Sun’s storms. Ulysses, SOHO, and Cluster together provide an extraordinary overview of solar behaviour and its effects, both near and far in the Solar System.

Original Source: ESA News Release

Image credit: NASA

Researchers at Harvard University demonstrated that they can slow light and even completely stop it for several thousandths of a second. They built a chamber containing a cloud of sodium atoms cooled to almost absolute zero and then fired a light pulse into this cloud. The pulse slowed to a stop and even turned off ? the researchers were able to revive it again by firing a laser into the cloud. Although this breakthrough happened a couple of years ago, and an upcoming special edition of Scientific American called ?The Edge of Physics? will provide an update to the research.

NASA-funded research at Harvard University, Cambridge, Mass., that literally stops light in its tracks, may someday lead to breakneck-speed computers that shelter enormous amounts of data from hackers.

The research, conducted by a team led by Dr. Lene Hau, a Harvard physics professor, is one of 12 research projects featured in a special edition of Scientific American entitled “The Edge of Physics,” available through May 31.

In their laboratory, Hau and her colleagues have been able to slow a pulse of light, and even stop it, for several-thousandths of a second. They’ve also created a roadblock for light, where they can shorten a light pulse by factors of a billion.

“This could open up a whole new way to use light, doing things we could only imagine before,” Hau said. “Until now, many technologies have been limited by the speed at which light travels.”

The speed of light is approximately 300,000 kilometers per second (about 186,000 miles per second or 670 million miles per hour). Some substances, like water and diamonds, can slow light to a limited extent. More drastic techniques are needed to dramatically reduce the speed of light. Hau’s team accomplished “light magic” by laser-cooling a cigar-shaped cloud of sodium atoms to one-billionth of a degree above absolute zero, the point where scientists believe no further cooling can occur. Using a powerful electromagnet, the researchers suspended the cloud in an ultra-high vacuum chamber, until it formed a frigid, swamp-like goop of atoms.

When they shot a light pulse into the cloud, it bogged down, slowed dramatically, eventually stopped, and turned off. The scientists later revived the light pulse and restored its normal speed by shooting an additional laser beam into the cloud.

Hau’s cold-atom research began in the mid-1990s, when she put ultra-cold atoms in such cramped quarters they formed a type of matter called a Bose-Einstein condensate. In this state, atoms behave oddly, and traditional laws of physics do not apply. Instead of bouncing off each other like bumper cars, the atoms join together and function as one entity.

The first slow-light breakthrough for Hau and her colleagues came in March 1998. Later that summer, they successfully slowed a light beam to 38 miles per hour, the speed of suburban traffic. That’s 2 million times slower than the speed of light in free space. By tinkering with the system, Hau and her team made light stop completely in the summer of 2000.

These breakthroughs may eventually be used in advanced optical-communication applications. “Light can carry enormous amounts of information through changes in its frequency, phase, intensity or other properties,” Hau said. When the light pulse stops its information is suspended and stored, just as information is stored in the memory of a computer. Light-carrying quantum bits could carry significantly more information than current computer bits. Quantum computers could also be more secure by encrypting information in elaborate codes that could be broken only by using a laser and complex decoding formulas.

Hau’s team is also using slow light as a completely new probe of the very odd properties of Bose-Einstein condensates. For example, with the light roadblock the team created, they can study waves and dramatic rotating-vortex patterns in the condensates.

The Harvard research team includes Hau; Drs. Zachary Dutton, Chien Liu, Brian Busch and Michael Budde; and graduate students Christopher Slowe, Naomi Ginsberg and Cyrus Behroozi. More information about Hau’s research is available on the Internet, at http://www.physics.harvard.edu/fac_staff/hau.html.

For information about NASA’s Fundamental Physics Program on the Internet, visit http://spaceresearch.nasa.gov or http://funphysics.jpl.nasa.gov.

Hau conducts research under NASA’s Fundamental Physics in Physical Sciences Research Program, part of the agency’s Office of Biological and Physical Research, Washington. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., a division of the California Institute of Technology, Pasadena, manages the Fundamental Physics program.

Original Source: NASA News Release