Archive for October 29, 2012

Galactic Thief: “I Would Have Gotten Away With It, If It Weren’t For Those Meddling Astronomers”

October 29, 2012 Leave a comment

One of the closest galaxies to the Milky Way almost got away with theft. However, new simulations convicted the Large Magellanic Cloud (LMC) of stealing stars from its neighbor, the Small Magellanic Cloud (SMC). And the crucial evidence came from surveys looking for something entirely different – dark objects on the outskirts of the Milky Way.

Astronomers have been monitoring the LMC to hunt for evidence of massive compact halo objects, or MACHOs. MACHOs were thought to be faint objects, roughly the mass of a star, but their exact nature was unknown. Several surveys looked for MACHOs in order to find out if they could be a major component of dark matter – the unseen stuff that holds galaxies together.

“We originally set out to understand the evolution of the interacting LMC and SMC galaxies,” explains lead author Gurtina Besla of Columbia University. “We were surprised that, in addition, we could rule out the idea that dark matter is contained in MACHOs.” “Instead of MACHOs, a trail of stars removed from the SMC is responsible for the microlensing events,” says co-author Avi Loeb of the Harvard-Smithsonian Center for Astrophysics. “You could say we discovered a crime of galactic proportions,” he adds.

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Voyager Observes Magnetic Field Fluctuations In Heliosheath

October 29, 2012 Leave a comment

As they near the outer reaches of the solar system, for the past several years the two Voyager spacecraft have been sending back observations that challenge scientists’ views of the physics at the edge of the heliosphere, the bubble created by charged particles flowing outward from the Sun. A new study looks at magnetic field fluctuations and cosmic ray intensity observed by Voyager I.

In 2004, Voyager I crossed the termination shock, the region where the solar wind begins to slow as it interacts with the interstellar medium. Just outside the termination shock is the heliosheath, where the solar wind continues to slow, reaching a stagnation region where solar wind speed drops to zero. Burlaga and Ness studied the magnetic field observed by Voyager I during 2010, when the spacecraft was moving through this stagnation region. Their analysis shows that magnetic field fluctuations outside the termination shock were primarily compressive fluctuations in field strength along the direction of the motion of the planets around the Sun. The fluctuations were observed on time scales of several hours.

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Super-Massive Black Hole Inflates Giant Bubble

October 29, 2012 Leave a comment

This false colour image shows the galaxy M87. Optical light is shown in white/blue (Credits: SDSS), the radio emission in yellow/orange (LOFAR). Credits: Francesco de Gasperin, on behalf of the LOFAR collaboration.

Using a brand-new radio telescope, astronomers have produced one of the best images ever made at the lowest frequencies of giant bubbles produced by a super-massive black hole. The observations were performed at frequencies ranging from 20 to 160 MHz which are normally used for communications by airplane pilots. The picture shows what looks like a giant balloon filled with radio emitting plasma, which exceeds the size of an entire galaxy.

Some black holes actively accrete matter. Part of this material does not fall into the black hole but is ejected in a narrow stream of particles, traveling at nearly the speed of light. When the stream slows down, it creates a tenuous balloon that can engulf the entire galaxy.

“The result is of great importance”, says Francesco de Gasperin, lead author of the study that will be published in the journal Astronomy & Astrophysics. “It shows the enormous potential of LOFAR, and provides compelling evidence of the close ties between black hole, host galaxy, and their surroundings. Like symbiotic species” adds de Gasperin, “a galaxy and its central black hole lead intimately connected lives, the galaxy providing matter to feed the black hole, and the black hole returning energy to the galaxy”.

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