Synopsis: Tidal Disruption of a Star

Theorists suggest that the weeks-long flare measured last year from a distant galaxy was probably beamed by a jet of material aligned with the rotational axis of a mammoth black hole.
Synopsis figure
NASA/Goddard Space Flight Center/Swift

The cores of most galaxies are thought to harbor black holes with masses of a million or more suns. But many remain unseen until an unlucky star passes too close and is pulled apart by tidal forces. The stellar debris gathers into a disk and spirals towards the black hole in the center. As it does, it may form a jet of material that beams high-energy light like a flashlight. Last spring, the Swift satellite measured a flare of x rays and gamma rays from a distant galaxy that has the hallmarks of such a jet that happens to point right at us.

Long-lived jets may explain many bright astronomical objects, such as quasars, but astrophysicists still have much to learn about how the jets form. In Physical Review Letters, Nicholas Stone and Abraham Loeb, both at Harvard University, argue that last year’s flare gives an important clue. The tidal disruption should have quickly formed a disk in the plane of the original star’s motion, which in general will not be perpendicular to the black hole’s rotation axis. Stone and Loeb calculate that the dragging of the relativistic frame by the mass of the rotating black hole will cause the disk to precess like a wobbling top. If the jet direction were determined by the disk, it would have quickly pointed away from us. Instead, the flare lasted more than two weeks, suggesting that the jet was directed along the unchanging axis of rotation for the black hole. – Don Monroe


More Features »


More Announcements »

Subject Areas


Previous Synopsis

Next Synopsis


And Then There Was One

Read More »

Related Articles

Synopsis: Neutrino Flashes from Exploding Stars

Synopsis: Neutrino Flashes from Exploding Stars

Calculations indicate that neutrino emission from a supernova could be detected on Earth, possibly revealing how the star explodes. Read More »

Synopsis: Cosmic Test of Quantum Mechanics
Quantum Physics

Synopsis: Cosmic Test of Quantum Mechanics

Light from two stars in the Milky Way has been used to test an open loophole of quantum physics. Read More »

Focus: Photons Brake the Sun
Plasma Physics

Focus: Photons Brake the Sun

Detailed solar observations and theory suggest that photons remove angular momentum from the Sun, explaining why the Sun’s surface spins more slowly than its core. Read More »

More Articles