Hubble and Einstein 'Weigh' Nearest White Dwarf Star

HUBBLE AND EINSTEIN "WEIGH" NEAREST WHITE DWARF STAR
From Lori Stiles, UA, University Communications, 520-621-1877
Tuesday, December 13, 2005

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Contact Information
Jay Holberg 520-621-4571
Ivan Hubeny 520-626-1470

Related Web sites with images
http://www.spacetelescope.org
http://hubblesite.org/news/2005/36
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Astronomers have used NASA's Hubble Space Telescope to get the most
precise
measurement ever made of a tiny shift in the light from Earth's nearest
white dwarf star and, using Einstein's theory of general relativity,
accurately determined the incredibly dense star's mass.

The white dwarf star, Sirius B, is a companion to Sirius A, the
brightest
star in the night sky. The binary star system is only 8.6 light years
from
Earth. (A light year is the distance light travels in one year, roughly
six
trillion miles.) But ground-based astronomers have found it impossible
to
precisely measure light from Sirius B because it is swamped by the
glare of
the ten-thousand times brighter Sirius A.

Jay B. Holberg and Ivan Hubeny of The University of Arizona are
members of
the team led by Martin Barstow of the University of Leicester, U.K.,
who
used the Hubble to get sharp views of just the white dwarf star,
unpolluted
by light from Sirius A. White dwarf stars are the dying remnant cores
of
stars similar to the sun. Our sun will eventually become a white dwarf.

Applying Einstein's general relativity theory, the team determined
that
Sirius B packs 98 percent of the mass of our sun within its 7,500-mile
diameter (12,000 kilometers), or within a volume slightly smaller than
Earth.

Albert Einstein proposed the general relativity theory in 1915. It
says
that the gravity of any mass, such as a planet or star, has the effect
of
warping the space and time around it.

Einstein predicted that astronomers would observe light losing a
fraction
of its energy because of a massive star's intense gravitational field.
They
would see light shifted to longer, redder wavelengths. The phenomenon
is
called "gravitational redshift" effect.

Sirius B has an intense gravitational field that warps space and slows
time
far more dramatically than we experience on Earth. If we humans were to
stand on Sirius B, we'd be crushed by space warped by gravity. A
150-pound
person would weigh 50 million pounds. (But on the upside, if we
Earthlings
could survive, we wouldn't age as quickly.)

"The nature of the ashes of these dead stars give us important clues
about
the lives and deaths of stars like our own sun," Barstow said. "The
nuclear
waste of carbon and oxygen produced in the process are essential
elements
for life and are eventually recycled into interstellar space to form
new
stars, planets and, possibly, living beings."

"Sirius' strange companion (Sirius B) has played a key role in the
development of physics and astrophysics since 1915, when it first
alerted
astronomers to the existence of enormously dense states of matter,"
Holberg
added.

Astronomers first measured the gravitational redshift in light from
Sirius
B in 1925, helping confirm Einstein's general relativity theory. As a
young
graduate student at Cambridge University in the early 1930s,
Subramanyan
Chandrasekhar used Einstein's theory of special relativity and quantum
mechanics to show how white dwarf stars could exist. He also deduced
that no
white dwarf could ever have more mass than 1.4 solar masses.
Chandrasekhar's
work was dismissed until the 1960s, then recognized with the Nobel
Prize in
physics in 1983.

The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency. The Space Telescope Science
Institute in Baltimore conducts Hubble science operations. The
institute is
operated for NASA by the Association of Universities for Research in
Astronomy, Inc., Washington.