These days, astronomers all over the world sleep with one eye open, keeping a close watch of of the supermassive black hole located in the center of our Milky Way Galaxy: Sagittarius A* (Sgr A*). A mysterious gas cloud called “G2” is on a collision course with our Galactic nucleus and may produce some fireworks in the near future (read all about it here).
Imagine the excitement when on April 24 (2013), our daily observations performed with Swift’s X-ray Telescope suddenly detected enhanced activity at the position of Sgr A*. An Astronomer’s Telegram was readily distributed to instantly notify the astronomical community. To everybody’s surprise, however, rapid follow-up observations at infrared and radio wavelengths did not detect anything out of the ordinary and in stead suggested the supermassive black hole remained quiet as always.
The mystery was resolved when right next day, Swift’s Burst Alert Telescope detected a very short (less than a second) and energetic burst of gamma-ray emission. Together with the detection of a pulsed X-ray signal using the brand-new high-energy telescope NuSTAR, this revealed that an otherwise dormant neutron star, located very close to the supermassive black hole, had been revived. This neutron star, named SGR J1745-29, has an extremely strong magnetic field and belongs to the rare class of “magnetars”. So far it is only the magnetar that continues to show fireworks, whereas Sgr A* remains as quiet as it has ever been.
Kennea et al. 2013, ApJ Letters 770, L24: Swift Discovery of a New Soft Gamma Repeater, SGR J1745-29, near Sagittarius A*
Paper link: ADS
Press item: Sky&Telescope feature