The Jet of Galaxy M87

For the first time, Hubble Space Telescope and radio telescopes reveal the mysterious region near a black hole at the heart of a distant galaxy M87 -- some 50 million light-years away in the constellation Virgo, where a powerful stream of subatomic particles spewing outward at nearly the speed of light is formed into a beam, or jet, that then goes nearly straight for thousands of light-years.

The top left picture is a radio image of M87, which is taken with the Very Large Array (VLA) radio telescope in February 1989. It shows giant bubble-like structures where radio emission is thought to be powered by the jets of subatomic particles coming from the the galaxy's central black hole. The false color corresponds to the intensity of the radio energy being emitted by the jet. The top right picture is a visible light image of the giant elliptical galaxy M87, which is taken with NASA Hubble Space Telescope's Wide Field Planetary Camera 2 in February 1998. It reveals a brilliant jet of high-speed electrons emitted from the nucleus (the diagonal line across the image). The bottom picture is a Very Long Baseline Array (VLBA) radio image of the region close to the black hole taken in March 1999, where an extragalactic jet is formed into a narrow beam. Again, the false color corresponds to the intensity of the radio energy being emitted by the jet. The red region is about 1/10 light-year across.

W. Junor, J. A. Biretta, and M. Livio [Nature 401, 891 (1999)] have shown that M87's jet is formed within a few tenths of a light-year of the galaxy's core, presumed to be a black hole three billion times more massive than the Sun. In the formation region, the jet is seen opening widely, at an angle of about 60 degrees, nearest the black hole, but is squeezed down to only 6 degrees a few light-years away.

Both radio observations with the VLBA and optical observations with the Hubble Space Telescope have measured the motions of concentrations of material in M87's jets, and have shown the material to be moving at apparent speeds greater than that of light. This "superluminal" motion is a geometric illusion created by material moving nearly, but under, the speed of light, but in a direction somewhat toward the Earth.

A super massive black hole with an accretion disk are believed to exist at the center of M87. The Hubble Space Telescope has been able to measure the velocity of a rotating hot gas disk in the core of M87. The measurement was made by studying how the light from the disk is redshifted and blueshifted -- as part of the swirling disk spins in earth's direction and the other side spins away from earth. The gas on one side of the disk is speeding away from Earth, at a speed of about 1.2 million miles per hour (550 kilometers per second). The gas on the other side of the disk is orbiting around at the same speed, but in the opposite direction, as it approaches viewers on Earth. Such a high velocity is a clear evidence for the existence of a massive black hole at the center.

M87 was discovered by the French astronomer Charles Messier in 1781. The jet was first seen in 1918 by Lick Observatory astronomer Heber Curtis, who described it as "a curious straight ray." It was the first jet ever observed in astronomy. We don't understand how the jet is formed and how it is collimated though more than eighty years have passed since its discovery.

-- From HST press release