Shining so brightly that they eclipse the ancient galaxies
that contain them, quasars are distant objects powered by black holes a billion
times as massive as our sun. These Poweful dynamos have fascinated
astronomers since their discovery half a century ago.
In the 1930s, Karl Jansky, a physicist with Bell Telephone
Laboratories, discovered that the static interference on transatlantic phone
lines was coming from the. Milky Way By the 1950s, astronomers were using radio
telescopes to probe the heavens, and pairing their signals with visible
examinations of the heavens.
However, some of the smaller point-source objects didn't
have a match. Astronomers called them "quasi-stellar radio sources,"
or "quasars," because the signals came from one place, like a
star. Naming them didn't help determine what these objects were. It took
years of study to realize that these distant specks, which seemed to indicate
stars, are created by particles accelerated at velocities approaching the speed
of light
light-speed jets
Scientists now suspect that the tiny, point-like glimmers
are actually signals from galactic nuclei outshining their host galaxies.
Quasars live only in galaxies with supermassive black holes— black holes
that contain billions of times the mass of the sun. Although light cannot
escape from the black hole itself, some signals can break free around its
edges. While some dust and gas fall into the black hole, other particles
are accelerated away from it at near the speed of light. The particles
stream away from the black hole in jets above and below it, transported by one
of the most powerful particle accelerators in the universe.
Most quasars have been found billions of light-years away.
Because it takes light time to travel, studying objects in space functions much
like a time machine; we see the object as it was when light left it, billions
of years ago. Thus, the farther away scientists look, the farther back in time
they can see. Most of the more than 2,000 known quasars existed in the early
life of the galaxy. Galaxies like the Milky Way may once have hosted a quasar
that has long been silent.
Quasars emit energies of millions, billions, or even
trillions of electron volts. This energy exceeds the total of the light of all
the stars within a galaxy. Thebrightest objects in the universe, they shine
anywhere from 10 to 100,000 times brighter than the Milky Way.
Family tree
Quasars are part of a class of objects known as active galactic
nuclei (AGN). Other classes include Seyfert galaxies and blazars. All three
require supermassive black holes to power them.
Seyfert galaxies are the lowest energy AGN, putting out only
about 100 kiloelectronvolts (KeV). Blazars, like their quasar cousins, put out
significantly more energy.
Many scientists think that the three types of AGNs are the
same objects, but with different perspectives. While the jets of quasars seem
to stream at an angle generally in the direction of Earth, blazars may point
their jets directly toward the planet. Although no jets are seen in Seyfert
galaxies, scientists think this may be because we view them from the side, so
all of the emission is pointed away from us and thus goes undetected.
