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! style="background-color: #FFFFC0;" colspan="2" | Astrometry
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| Spectral type

Stellar classification

In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...

 
| F5IV
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| Apparent magnitude

Apparent magnitude

The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 (V)
| 17.0
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| Distance

Cosmic distance ladder

The cosmic distance ladder is the succession of methods by which astronomers determine the distances to celestial objects. A real direct distance measurement of an astronomical object is possible only for those objects that are "close enough" to Earth...

 
| 5,500—11,000 ly

Light-year

A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...

GRO J1655-40 is a binary star consisting of an evolved F5 primary star and a massive, unseen companion, which orbit each other once every 2.6 days in the constellation of Scorpius

Scorpius

Scorpius, sometimes known as Scorpio, is one of the constellations of the zodiac. Its name is Latin for scorpion, and its symbol is . It lies between Libra to the west and Sagittarius to the east...

.
Gas from the surface of the visible star is accreted onto the dark companion, which appears to be a stellar black hole

Stellar black hole

A stellar black hole is a black hole formed by the gravitational collapse of a massive star. They have masses ranging from about 3 to several tens of solar masses...

 with several times the mass of the Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

.
The optical companion of this low-mass X-ray binary is a subgiant F star.

Along with GRS 1915+105

GRS 1915+105

GRS 1915+105 or V1487 Aquilae is an X-ray binary star system which features a regular star and a black hole. It was discovered on August 15, 1992 by the WATCH all-sky monitor aboard Granat. "GRS" stands for "GRANAT source", "1915" is the right ascension and "105" is declination in units of 0.1...

, GRO J1655-40 is one of at least two galactic "microquasars" that may provide a link between the supermassive black hole

Supermassive black hole

A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...

s generally believed to power extragalactic quasar

Quasar

A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...

s and more local accreting black hole systems.
In particular, both display the radio jets

Relativistic jet

Relativistic jets are extremely powerful jets of plasma which emerge from presumed massive objects at the centers of some active galaxies, notably radio galaxies and quasars. Their lengths can reach several thousand or even hundreds of thousands of light years...

 characteristic of many active galactic nuclei.

The distance from our Solar System is probably about 11,000 light years, or approximately half-way from the Sun to the galactic center

Galactic Center

The Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc from the Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest...

, but a closer distance (~2800 lt yrs) is not ruled out.
GRO J1655-40 and its companion are moving through the Milky Way

Milky Way

The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

 at around 112 km/s (250,000 miles per hour), in a galactic orbit that depends on its exact distance, but is mostly interior to the "Solar circle", d~8,500 pc, and within 150 pc (~500 lt yrs) of the galactic plane.
For comparison, the Sun and other nearby stars have typical speeds on the order of 20 km/s relative to the average velocity of stars moving with the galactic disk's rotation in the solar neighborhood, which supports the idea that the black hole formed from the collapse of the core of a massive star.
As the core collapsed, its outer layers exploded as a supernova

Supernova

A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...

.
Such explosions often seem to leave the remnant system moving through the galaxy with unusually high speed.

External links

• http://blackholes.stardate.org/directory/factsheet.php?id=11
• Simbad