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Cosmic Searchlight  Streaming
out from the center of the galaxy M87 like a cosmic
searchlight is one of nature's most amazing phenomena, a
black-hole-powered jet of electrons and other sub-atomic
particles traveling at nearly the speed of light. In this
NASA Hubble Space Telescope image, the blue of the jet
contrasts with the yellow glow from the combined light of
billions of unseen stars and the yellow, point-like
globular clusters that make up this galaxy.
At first glance, M87 (also
known as NGC 4486) appears to be an ordinary giant
elliptical galaxy; one of many ellipticals in the nearby
Virgo cluster of galaxies. However, as early as 1918,
astronomer H.D. Curtis noted a "curious straight ray"
protruding from M87. In the 1950s when the field of radio
was blossoming, one of the brightest radio sources in the
sky, Virgo A, was discovered to be associated with M87
and its jet.
After decades of study,
prompted by these discoveries, the source of this
incredible amount of energy powering the jet has become
clear. Lying at the center of M87 is a supermassive black
hole, which has swallowed up a mass equivalent to 2
billion times the mass of our Sun. The jet originates in
the disk of superheated gas swirling around this black
hole and is propelled and concentrated by the intense,
twisted magnetic fields trapped within this plasma. The
light that we see (and the radio emission) is produced by
electrons twisting along magnetic field lines in the jet,
a process known as synchrotron radiation, which gives the
jet its bluish tint.
M87 is one of the nearest
and is the most well-studied extragalactic jet, but many
others exist. Wherever a massive black hole is feeding on
a particularly rich diet of disrupted stars, gas, and
dust, the conditions are right for the formation of a jet.
Interestingly, a similar phenomenon occurs around young
stars, though at much smaller scales and energies.
At a distance of 50
million light-years, M87 is too distant for Hubble to
discern individual stars. The dozens of star-like points
swarming about M87 are, instead, themselves clusters of
hundreds of thousands of stars each. An estimated 15,000
globular clusters formed very early in the history of
this galaxy and are older than the second generation of
stars, which huddle closer to the center of the galaxy.
Credit: NASA and The Hubble
Heritage Team (STScI/AURA)
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