Friday, December 11, 2015

Magnetic Fields Power Supermassive Black Hole, Sagittarius A*, Found In Our Milky Way Galaxy

Black Holes: writes on its site: “In this artist’s conception, the black hole at the center of our galaxy is surrounded by a hot disk of accreting material. Blue lines trace magnetic fields. The Event Horizon Telescope has measured those magnetic fields for the first time with a resolution six times the size of the event horizon (6 Schwarzschild radii). It found the fields in the disk to be disorderly, with jumbled loops and whorls resembling intertwined spaghetti. In contrast, other regions showed a much more organized pattern, possibly in the region where jets (shown by the narrow yellow streamer) would be generated. 
Illustration Credit: M. Weiss;CfA
An article in Physics. org reports on an astounding finding where magnetic fields have been found near an event horizon of a supermassive black hole in our galaxy, the Milky Way. (An event horizon is the boundary around the “mouth” of the black hole, where light can no longer escape.) The one in question is named Sagittarius A*, about 25,000 light-years from Earth and about 4 million times more massive than the sun. The event horizon, however, is 8 million miles (12.9 million kilometres) wide, which is less than the average distance from Mercury to the sun.

The article (“Event Horizon Telescope reveals magnetic fields at Milky Way’s central black hole;” December 3, 2015) says:
Most people think of black holes as giant vacuum cleaners sucking in everything that gets too close. But the supermassive black holes at the centers of galaxies are more like cosmic engines, converting energy from infalling matter into intense radiation that can outshine the combined light from all surrounding stars. If the black hole is spinning, it can generate strong jets that blast across thousands of light-years and shape entire galaxies. These black hole engines are thought to be powered by magnetic fields. For the first time, astronomers have detected magnetic fields just outside the event horizon of the black hole at the center of our Milky Way galaxy.

“Understanding these magnetic fields is critical. Nobody has been able to resolve magnetic fields near the event horizon until now,” says lead author Michael Johnson of the Harvard-Smithsonian Center for Astrophysics (CfA). The results appear in the Dec. 4th issue of the journal Science.
“These magnetic fields have been predicted to exist, but no one has seen them before. Our data puts decades of theoretical work on solid observational ground,” adds principal investigator Shep Doeleman (CfA/MIT), who is assistant director of MIT’s Haystack Observatory. This feat was achieved using the Event Horizon Telescope (EHT)—a global network of radio telescopes that link together to function as one giant telescope the size of Earth. Since larger telescopes can provide greater detail, the EHT ultimately will resolve features as small as 15 micro-arcseconds. (An arcsecond is 1/3600 of a degree, and 15 micro-arcseconds is the angular equivalent of seeing a golf ball on the moon.)
The next step for astrophysicists is to answer why certain black holes are so bright. If even light can’t escape a black hole, the expectation is that it would be dark. Yet, some black holes outshine the stars around them; one is the system ULX-1. What is known is that even as black holes suck in light, they also emit radiation.

The knowledge of black holes has a history of almost a century, Nola Taylor Redd writes (“Black holes, Facts, Theories & Definitions;” April 9, 2015) in “Albert Einstein first predicted black holes in 1916 with his general theory of relativity. The term "black hole" was coined in 1967 by American astronomer John Wheeler, and the first one was discovered in 1971.”

Supermassive black holes are among the the three kinds of black holes that astrophysicists have thus far identified; the other two are stellar black holes and intermediate black holes. What a fascinating galaxy we reside in, and are a part of; and a strange one, too.

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