Hubble's Constant And The Expanding Universe (I)
Explanation:
Our Universe is expanding. Distant galaxies appear to recede from us
at ever-increasing speeds. What is the rate of expansion? How long has it
been expanding? What will be its ultimate fate?
Two groups of astronomers
are searching vigorously for answers to these fundamental
questions using the Hubble Space Telescope (HST).
The teams
have recently announced conflicting measurements of
the Hubble constant,
a number which represents the expansion rate of the Universe.
Astronomer Wendy Freedman and her collaborators
have used pulsating stars called
Cepheids to measure the distance to galaxies like the Fornax cluster
barred spiral galaxy NGC1365 shown above. The ground based
photo (left) shows an inset locating the HST image (right)
which Freedman and team have used to identify some 50 Cepheids.
Their distance and velocity measurements determine Hubble's constant
to be about 80 kilometers per second per megaparsec which means that galaxies
one megaparsec (3 million lightyears) distant appear to recede from
us at a speed of 80 kilometers per second.
Conflicting results indicating a substantially slower expansion rate
(smaller Hubble constant)
are being reported by astronomer Allan Sandage and collaborators.
The value of Hubble's constant was recently the subject of a popular
public debate titled
"The Scale of the Universe 1996: The Value of Hubble's Constant".
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:
LHEA at
NASA /
GSFC
& Michigan Tech. U.
