Astronomy Picture of the Day |
APOD: 2001 December 19 - Finding Dark Matter
Explanation:
Where is
dark matter?
Galaxies rotate and move in
clusters as if a tremendous amount of
unseen matter is present.
But does dark matter exist in the greater universe too --
and if so, where?
The answer can be found by comparing the
distribution of galaxies
observed with
numerical simulations.
This comparison became much more accurate recently
when over 100,000 galaxy observations from the
2-Degree Field Galactic Redshift Survey were used.
In the above frame from a
computer simulation of our
universe,
a 300 million light-year slice shows
dark matter in gray and galaxies as colored circles.
The red box indicates the location of a rich
cluster of galaxies, while the green box shows a
more typical cross-section of
our universe.
Analyses indicate that the immense gravity of the pervasive dark matter pulls normal matter to it, so that
light matter and dark matter actually
cluster together.
APOD: 2003 August 14 - Dark Matter Map
Explanation:
The total mass within giant galaxy cluster
CL0025+1654,
about 4.5 billion
light-years away,
produces a cosmic gravitational lens --
bending
light as predicted
by Einstein's theory of gravity and forming detectable images
of even more distant background galaxies.
Of course, the total
cluster mass is the sum of the
galaxies themselves, seen as
ordinary luminous matter, plus the cluster's
invisible dark matter whose
nature
remains unknown.
But by analyzing the distribution of luminous matter and the
properties of the gravitational lensing
due to total cluster mass,
researchers have solved the problem of tracing
the dark matter layout.
Their resulting map
shows the otherwise invisible dark matter in blue,
and the positions of the cluster
galaxies in yellow.
The work,
based on extensive Hubble Space Telescope observations,
reveals that the cluster's
dark
matter is not evenly distributed, but
follows the clumps of luminous matter closely.
APOD: 2005 September 25 - WMAP Resolves the Universe
Explanation:
Analyses of a new high-resolution map of
microwave light emitted only 380,000 years after the
Big Bang appear to define
our universe
more precisely than ever before.
The eagerly awaited results announced last year from the orbiting
Wilkinson
Microwave Anisotropy Probe resolve several
long-standing disagreements in
cosmology rooted in less precise data.
Specifically,
present analyses of
above WMAP all-sky image
indicate that the universe is 13.7 billion years old
(accurate to 1 percent), composed of 73 percent
dark energy, 23 percent
cold
dark matter, and only 4 percent
atoms,
is currently expanding at the rate of 71 km/sec/Mpc (accurate to 5 percent),
underwent episodes of rapid expansion called
inflation, and will
expand forever.
Authors & editors:
Robert Nemiroff
(MTU) &
Jerry Bonnell
(USRA)
NASA Web Site Statements, Warnings, and
Disclaimers
NASA Official: Jay Norris.
Specific rights apply.
A service of:
EUD at
NASA /
GSFC
& Michigan Tech. U.