Astronomy Picture of the Day |
APOD: 1998 December 11 - High Redshift Quasars
Explanation:
Each red speck indicated above is a
powerful quasar estimated
to be over 100 times brighter than a galaxy.
Yet in these
Sloan Digital Sky Survey discovery images the
quasars
appear faint because they are extremely distant.
Their distances have been indirectly gauged
by noting how much the light they emit
has been stretched to longer wavelengths by the
expansion of the Universe.
Because red light has the longest wavelengths in the visible
spectrum,
this stretch has come to be called "redshift" - the greater the distance,
the greater the redshift.
Astronomers use a number known as "Z" to quantify this
cosmological redshift and the
quasar at the left, with a Z of 5, was
just proclaimed the new quasar redshift champion
(from left to right the measured Zs are 5.00, 4.90, 4.75).
What's the actual
distance to quasars with Zs of 5 or so?
... about 15 billion light-years, give or take a few billion light-years
depending on your
favorite cosmology!
APOD: 1997 December 6 - A Quasar Portrait Gallery
Explanation:
QUASARs (QUASi-stellAR objects)
lie near
the edge of the observable Universe.
Discovered in 1963,
astronomers were astounded that such objects could be
visible across billions of light-years, as this implies
they must emit prodigious
amounts of energy. Where does the energy come from?
Many believe
the quasar's central engine is a giant black hole
fueled by tremendous amounts of infalling gas, dust, and stars.
This gallery of quasar portraits from the Hubble Space
Telescope offers a look at their local neighborhoods: the quasars themselves
appear as the bright star-like objects with
diffraction spikes.
The images in the center and right hand columns reveal quasars
associated with disrupted colliding and merging galaxies
which should provide
plenty of debris to feed a hungry
black hole.
APOD: 1999 December 26 - Gamma-Ray Quasar
Explanation:
The bright object in the center of the false color
image above is quasar 3C279
viewed in gamma-rays, photons with
more than 40 million times the energy of visible light.
Like all quasars, 3C279 is a nondescript, faint, star-like object in
the visible sky.
Yet, in June of 1991 a gamma-ray telescope onboard NASA's orbiting
Compton Gamma Ray Observatory unexpectedly
discovered that it was one of the
brightest objects in the gamma-ray sky.
Shortly after this image was recorded
the quasar faded from view at gamma-ray energies.
Astronomers are still trying to understand what causes these enigmatic
objects to flare so violently.
Another quasar, 3C273, is faintly
visible above and to the right of center.
Authors & editors:
Robert
Nemiroff
(MTU)
& Jerry Bonnell (USRA)
NASA Technical Rep.:
Jay Norris.
Specific rights apply.
A service of:
LHEA at
NASA/
GSFC
&
Michigan Tech. U.