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Black Holes Encyclopedia

XTE J1650-500

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Stellar mass


In the constellation Ara


26,000 light-years


3.8 times the mass of the Sun


Diameter 14 miles (23 km)

Discovery Methods


XTE J1650-500

We can know only two things about a black hole: its mass and how fast it spins. In the case of a black hole in a system known as XTE J1650-500, astronomers know both. And each number has helped expand our knowledge of all black holes.

Astronomers discovered the system in 2001 in observations by an orbiting X-ray telescope known as Rossi X-Ray Timing Explorer. The satellite revealed an accretion disk encircling a black hole several times as massive as the Sun.

Observations by RXTE and another X-ray satellite, XMM-Newton, also revealed that the inner edge of the superheated accretion disk was within about 20 miles (30 km) of the black hole's event horizon. The close proximity told astronomers that the black hole is spinning rapidly, because the accretion disk can encroach much closer to a spinning black hole than one that is stationary.

In 2008, astronomers Nikolai Shaposhnikov and Lev Titarchuk of the Goddard Space Flight Center reported that they had determined the black hole's mass: about 3.8 times the mass of the Sun.

The astronomers found a pattern of changes in the X-ray energy from XTE J1650-500. In studies of other black holes in which the masses had been determined from other methods, the astronomers found that the oscillations vary with the black hole's mass. The oscillations from XTE J1650-500 revealed that it is the least-massive black hole yet discovered.

The theoretical lower limit for a black hole is about 1.7 to 2.7 times the mass of the Sun. Anything below that limit should form a less-dense neutron star. By measuring the weight of such a small black hole, the astronomers pushed closer to the lower limit.


Scientists Identify Smallest Known Black Hole (NASA)
A black hole in a star system known as XTE J1650-500 is the smallest and least-massive black hole yet discovered, at less than four times the mass of the Sun. That is close to the expected limit for how small a black hole can be.



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This document was last modified: July 13, 2010.


Superhot Gas Around XTE J1650-500
Artist's Rendering

Rossi X-Ray Timing Explorer
Artist's Rendering


No animations available for this black hole.