Sky and Telescope - February 2016 - 16
Galactic Center Goings-On
Intothe
Heart
DARYL HAGGARD &
GEOFFREY C. BOWER
WHEN ASTRONOMERS TUNED IN TO WATCH OUR GALAXY'S SUPERMASSIVE BLACK
HOLE FEED, THEY FOUND MORE (AND LESS) THAN THEY EXPECTED.
THE MILKY WAY GALAXY'S nucleus is full of surprises. Scientists began to uncover exotic phenomena
there more than 40 years ago, when they discovered the
supermassive black hole, Sagittarius A* (Sgr A*, pronounced "saj A-star"), lurking at its core. Over the last
several years, galactic-center happenings have been particularly spectacular and unpredictable. In 2012, observers
reported a small, dusty object nicknamed G2 plummeting
toward the black hole. All eyes (and telescopes!) turned to
watch this little daredevil's destruction.
Across the globe, astronomers followed G2's fall,
monitoring it across the electromagnetic spectrum for
many months, hoping to discern the object's structure
and fate. And then, before our telescopic eyes, something completely unexpected appeared. In early 2013,
several months before G2's closest approach to Sgr A*,
astronomers caught a bright X-ray outburst. But it didn't
come from the black hole. The combined X-ray powers of
the Swift, NUSTAR, and Chandra observatories quickly
16
Februar y 2016 sky & telescope
revealed that this newcomer was a magnetar, a young,
highly magnetic neutron star - the first of its kind to
be seen in the galactic center. Rapid radio follow-up conclusively placed this object at the distance of the galactic
center, very likely in orbit around the black hole (though
at a larger distance than G2).
After all this action, Sgr A* would not be outdone.
Later, in September 2013 and again in October 2014, Sgr
A* shot off two of the brightest X-ray flares we've ever
observed. Rich data from the G2- and magnetar-monitoring campaigns offered an unprecedented multiwavelength view of these bright flares. These observations
may hold the keys to understanding the environment
around our nearest supermassive black hole.
The G2 Encounter
In 2012, a team of scientists led by Stefan Gillessen (Max
Planck Institute for Extraterrestrial Physics, Germany)
reported the discovery of G2, a faint infrared blob on a
Sky and Telescope - February 2016
Table of Contents for the Digital Edition of Sky and Telescope - February 2016
Contents
Sky and Telescope - February 2016 - Cover1
Sky and Telescope - February 2016 - Cover2
Sky and Telescope - February 2016 - 1
Sky and Telescope - February 2016 - Contents
Sky and Telescope - February 2016 - 3
Sky and Telescope - February 2016 - A
Sky and Telescope - February 2016 - B
Sky and Telescope - February 2016 - 4
Sky and Telescope - February 2016 - 5
Sky and Telescope - February 2016 - 6
Sky and Telescope - February 2016 - 7
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Sky and Telescope - February 2016 - Cover3
Sky and Telescope - February 2016 - Cover4
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