Multi-wavelength View of the Radio Galaxy Hercules A
Spectacular jets powered by the gravitational energy of a supermassive
black hole in the core of the elliptical galaxy Hercules A illustrate
the combined imaging power of two of astronomy's cutting-edge tools,
the Hubble Space Telescope's Wide Field Camera 3, and the recently
upgraded Karl G. Jansky Very Large Array (VLA) radio telescope in
Some two billion light-years away, the yellowish elliptical galaxy in
the center of the image appears quite ordinary as seen by Hubble in
visible wavelengths of light. The galaxy is roughly 1,000 times more
massive than our Milky Way and harbors a 2.5-billion-solar-mass
central black hole that is 1,000 times more massive than the black hole
in the Milky Way. But the innocuous-looking galaxy, also known as
3C 348, has long been known as the brightest radio-emitting object in
the constellation Hercules. Emitting nearly a billion times more power
in radio wavelengths than our Sun, the galaxy is one of the brightest
extragalactic radio sources in the entire sky.
The VLA radio data reveal enormous, optically invisible jets that, at
one-and-a-half million light-years long, dwarf the visible galaxy from
which they emerge. The jets are very-high-energy plasma beams,
subatomic particles and magnetic fields shot at nearly the speed of
light from the vicinity of the black hole. The outer portions of both
jets show unusual ring-like structures suggesting a history of multiple
outbursts from the supermassive black hole at the center of the galaxy.
The innermost parts of the jets are not visible because of the extreme
velocity of the material; relativistic effects confine all of the light
to a narrow cone aligned with the jets, and so that light is not seen by us.
Far from the galaxy, the jets become unstable and break up into
rings and wisps.
The entire radio source is surrounded by a very hot, X-ray-emitting
cloud of gas, not seen in this optical-radio composite.
Hubble's view of the field also shows a companion elliptical galaxy very
close to the center of the optical-radio source, which may be merging
with the central galaxy. Several other elliptical and spiral galaxies
that are visible in the Hubble data may be members of a cluster of galaxies.
Hercules A is by far the brightest and most massive galaxy in the cluster.
Credit: NASA, ESA, S. Baum and C. O'Dea (RIT), R. Perley and W. Cotton
(NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA)