Type

Stellar mass

Location

in the constellation Aquila

Distance

8,100 light-years (2500 parsecs)

Mass

14 times the mass of the Sun

Size

Diameter roughly 50 miles (85 km) equal to the size of a large city

Discovery Methods

• Detection of a jet
• Detection of an accretion disk
• Measuring the motions of a companion star

GRS 1915+105

Like all of the stellar-mass black holes discovered to date, GRS 1915+105 is "fed" by an accretion disk -- a maelstrom of superhot gas pulled from the surface of a companion star. In the case of GRS 1915, though, it's not a smooth process. The disk occasionally "hiccups," sending material in the inner part of the disk plunging into the black hole. X-rays from the inner disk heat the outer disk create strong winds that blow away a lot of material. And the winds may periodically shut down a jet of material that shoots into space from the poles of the black hole.

GRS consists of a black hole about 14 times as massive as the Sun and a companion star about 1.2 times the Sun's mass.

In 1994, astronomers discovered that the system shoots strong jets of electrically charged particles into space from just above the black hole's north and south poles. The jets are described as "superluminal," which means they look like they are traveling faster than the speed of light. A detailed analysis, though, shows that the jets fire at about 90 percent of lightspeed, with odd electromagnetic effects making them look faster.

The jets are fed by material from the accretion disk, which is one of the brightest black-hole disks yet discovered in the Milky Way galaxy. Magnetic fields created by the swirling masses of electrically charged gas funnel some of the material into the twin jets.

Much of the energy emitted by the accretion disk is in the form of X-rays, which have been studied by several space observatories, including NASA's Chandra X-Ray Observatory and Rossi X-Ray Timing Explorer. Their observations have revealed that the disk pulses like a beating heart.

The black hole is spinning so fast that the gas in the disk can spiral to within about five miles of the black hole's surface, known as the event horizon, before it either plunges into the black hole or is blown back into space through the jets.

At that distance, the disk material is spiraling at about half of the speed of light, so it produces enormous amounts of radiation. The radiation pushes material in the inner part of the disk away from the black hole. As the gas piles up it gets hotter and hotter, producing more and more X-rays. Eventually, this band of superheated gas collapses and falls into the black hole. As the process repeats it creates pulses of X-rays that resemble the beating of a human heart.

The X-rays heat the outer portions of the accretion disk, causing it to produce a strong wind that blows some of the material out into space. The wind gets so strong that the disk loses more material than it receives from the companion star. With less material feeding the black hole, the jets shut down.

Over time, though, the wind subsides and material in the disk once again spirals closer to the black hole, causing the process to repeat itself.

The astronomers who study GRS 1915 say this process may be a sort of self-regulation that keeps the black hole from growing.

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This document was last modified: June 28, 2011.