GRS 1915+105

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Lore & Background

In 1994, GRS 1915+105 became the first known galactic source that ejects material with apparent superluminal motion velocities. Observations with high resolution radio telescopes such as VLA, MERLIN, and VLBI show a bi-polar outflow of charged particles, which emit synchrotron radiation at radio frequencies. These studies have shown that the apparent superluminal motion is due to a relativistic effect known as relativistic aberration, where the intrinsic velocity of ejecta is actually about 90% the speed of light. Repeat observations by the Chandra X-Ray Observatory over the period of a decade have revealed what may be a mechanism for self-regulation of the rate of growth of GRS 1915+105. The jet of materials being ejected is occasionally choked off by a hot wind blowing off the accretion disk. The wind deprives the jet of materials needed to sustain it. When the wind dies down, the jet returns.

In Their Own Story

The sensors screamed before the visual array could even adjust. A knot of plasma, superheated to millions of degrees, tore itself free from the accretion disk and launched outward—a silent, relativistic bullet of pure energy. To a distant observer, this blob seemed to defy the cosmic speed limit, racing across the sky faster than light itself. It was an optical ghost, a sleight-of-hand by relativity where time bent around the black hole's voracious hunger. Meanwhile, its companion star, a main sequence star, continued its slow sacrifice, feeding another stream of gas into the invisible maw that spun so violently it threatened to rip spacetime apart—a miniature quasar roaring in the dark heart of Aquila.

Reader's Guide

Unlike supermassive black holes found in galactic centers, this object possesses 10 to 18 solar masses but generates jets of plasma that move at relativistic speeds, about 90% the speed of light. These jets are powered by the transfer of material from the star to the black hole. The system is famous for exhibiting apparent superluminal motion. When jet material travels toward Earth at nearly the speed of light, the time difference between photons emitted at different points along the path compresses, creating the illusion that the object is moving faster than light. This phenomenon provided the first known galactic source of apparent superluminal motion. Its dimensionless spin parameter is >0.82, indicating it rotates at least 950 times per second. This extreme rotation drives powerful frame-dragging effects, where spacetime itself is twisted around the event horizon. Studying this object allows astrophysicists to probe the innermost stable circular orbit and test the limits of black hole thermodynamics in a laboratory within our own galaxy.

Did You Know?

• GRS 1915+105 was discovered on August 15, 1992 by the WATCH all-sky monitor aboard Granat.
• It became the first known galactic source that ejects material with apparent superluminal motion velocities in 1994.
• The black hole rotates at least 950 times per second, giving it a spin parameter >0.82.
• The intrinsic velocity of the ejecta is actually about 90% the speed of light.
• The jet is occasionally choked off by a hot wind blowing off the accretion disk, as revealed by repeat Chandra X-Ray Observatory observations over a decade.