NGC 4319 AND MARKARIAN 205: ODD COUPLE WIDELY SEPARATED BY TIME AND SPACE
Appearances can be deceiving. In this NASA Hubble
Space Telescope image, an odd celestial duo, the
spiral galaxy NGC 4319 [center] and a quasar called
Markarian 205 [upper right], appear to be neighbors.
In reality, the two objects don't even live in the
same city. They are separated by time and space.
NGC 4319 is 80 million light-years from Earth.
Markarian 205 (Mrk 205) is more than 14 times farther
away, residing 1 billion light-years from Earth.
The apparent close alignment of Mrk 205 and NGC
4319 is simply a matter of chance. Astronomers used
two methods to determine the distances to these
objects. First, they measured how their light has
been stretched in space due to the universe's expansion.
Then they measured how much the ultraviolet light
from Mrk 205 dimmed as it passed through the interstellar
gas of NGC 4319.
The Hubble image shows the inner region of NGC
4319. In addition to the galaxy's inner spiral arms,
an outer arm is faintly visible at lower left. The
unusually dark and misshapen dust lanes in the galaxy's
inner region are evidence of a disturbance, probably
caused by an earlier interaction with another galaxy,
NGC 4291, which is not in the photograph.
At a distance of 1 billion light-years, Mrk 205
is a relatively nearby quasar. Many quasars reside
much farther away. Quasars, once known only as mysterious
point-like objects, are now known to be distant
galaxies that have extremely bright cores. These
powerhouses of light are probably fueled by massive
black holes. With powerful telescopes like Hubble,
it is often possible to see the quasar's surrounding
halo of faint starlight, as is clearly visible around
Mrk 205 has a companion, a compact galaxy just
below it. The objects appear to be interacting.
The compact galaxy may be responsible for the structure
in Mrk 205's halo.
The Hubble image shows that interacting galaxies
and disturbances within galaxies are a rich source
of information about galaxy structure and evolution.
The pair, NGC 4319 and Mrk 205, is of particular
interest to astronomers because of the role they
played in a three-decades-old scientific controversy.
Astronomer Halton Arp identified a number of galaxy-quasar
pairings and argued that the quasars were at the
same distance as the galaxies, not the much larger
distances indicated by their redshifts. NGC 4319
and Mrk 205 were the most famous example because
in some ground-based images they appeared to be
linked by a "luminous bridge". An overwhelming
abundance of evidence long ago convinced virtually
all astronomers that quasars are indeed at the vast
distances indicated by their redshifts, but this
controversy remains as an interesting example of
how science judges and incorporates new ideas and
novel phenomena. You can learn more about this controversy
by visiting the More
Images link on this month's Hubble Heritage
Credits: NASA and the Hubble Heritage Team (STScI/AURA)
Acknowledgment: R. Knacke (Penn State Erie)