From: LARRY KLAES (ljk4@msn.com)
Date: Thu Nov 07 2002 - 08:33:26 PST
----- Original Message -----
From: Mark Hess
Sent: Monday, November 04, 2002 3:38 PM
To: News Media list.serv
Subject: SCIENTISTS MEASURE THE MOST POWERFUL MAGNET KNOWN
Bill Steigerwald
November 4, 2002
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301 286 5017)
wsteiger@pop100.gsfc.nasa.gov
RELEASE: 02-156
SCIENTISTS MEASURE THE MOST POWERFUL MAGNET KNOWN
Scientists have identified the most magnetic object known in the
Universe, the result of the first direct measurement of a magnetic
field around a peculiar neutron star first observed nearly 25 years
ago.
By following the fate of a tiny proton whipping about at near light
speed close to the neutron star with NASA's Rossi X-ray Explorer
satellite, scientists calculated this star's magnetic field to be up
to 10 times more powerful than previously thought -- with a force
strong enough to slow a steel locomotive from as far away as the Moon.
This object, named SGR 1806-20, is one of only 10 unusual neutron
stars classified as magnetars, thousands of times more magnetic than
ordinary neutron stars and billions of times more magnetic than the
most powerful magnets built on Earth. The strength of its magnetic
field is approximately a million billion (10^15) Gauss, according to
a team led by Alaa Ibrahim, a doctoral candidate at George Washington
University conducting research at NASA's Goddard Space Flight Center
in Greenbelt, Md.
Other magnetars could be just as magnetic, although direct
measurements have not yet been made, the team said. The Sun's average
magnetic field (or dipole), in comparison, varies between 1 and 5
Gauss. Results are published in two articles in the Astrophysical
Journal Letters.
"If this magnetar were as close as the Moon, it would rearrange the
molecules in our bodies," said Ibrahim. SGR 1806-20, however, is a
safe 40,000 light years from Earth. (One light year is about six
trillion miles or 9.5 trillion km.) "Although one would not want to
get close to such an object, we now have a method of probing from
afar to learn about the physics of matter under extreme gravitational
and magnetic forces."
A neutron star is a compact sphere approximately 10 miles (16 km)
wide, the core remains of a collapsed star once roughly ten time more
massive than the Sun. In 1979, scientists observed a huge outburst
from a neutron star, which, upon further analysis, marked the
discovery of a new class of neutron stars now known as Soft Gamma-ray
Repeaters (SGR). Scientists theorized that these objects must be
highly magnetic in order to burst with such magnitude, and they
coined the term "magnetar."
Scientists have estimated SGR magnetic fields by measuring the spin
rate of the star along with the spin-down rate, that is, the rate at
which the star's spin is slowing. Two scientists who have led this
effort are Dr. Chryssa Kouveliotou of NASA's Marshall Space Flight
Center and Dr. Kevin Hurley of the University of California at
Berkeley. This is an indirect measure of magnetic field strength,
for strong magnetic fields are thought to put the brakes on a
spinning neutron star. The long-standing estimate has been over
10^14 Gauss.
Ibrahim's team identified an energy feature in many of the bursts
emanating from SGR 1806-20. In analyzing the bursts spectral
features, which is a graph showing the energy level emitted by light
close to the neutron star surface, the team found a specific energy
manifested at 5,000 electron volts.
This energy level, Ibrahim said, corresponds precisely to the energy
needed to excite a proton trapped in an immense 10^15 Gauss magnetic
field. This fits the magnetar "starquake" model, analogous to an
earthquake, in which the surface of the neutron star momentarily
cracks open and ejects protons. The quake itself is the source of the
bursting seen in magnetars, or SGRs, and the ejected protons get
trapped in the star's strong magnetic field loops.
These results on the proton feature meet theoretical predictions made
by a number of scientists, including Drs. Silvia Zane of the Mullard
Space Science Laboratory in the United Kingdom and Roberto Turolla of
the University of Podova, Italy. However, other theorists expected
the effect to be very difficult to observe.
Dr. Jean Swank of NASA Goddard, a co-author and the Rossi Explorer
Project Scientist, noted that while electron signatures have provided
key information about typical neutron stars powered by rotation and
gravitation, protons are now revealing their presence in magnetars,
providing exciting new information about these mysterious objects.
Co-authors of the Astrophysical Journal Letter reports are Dr.
William Parke of the George Washington University in Washington,
D.C., and Dr. Samar Safi-Harb of the University of Manitoba, Canada,
in addition to Swank, Zane and Turolla. The Rossi Explorer was
launched in December 1995. NASA Goddard manages the day-to-day
operation of the satellite and maintains its data archive.
For an image and more information, refer to:
http://www.gsfc.nasa.gov/topstory/20021030strongestmag.html
For animation of a magnetar, refer to:
http://nt.phys.gwu.edu/~kovac/magnetar/
-end-
GSFC news
and links to other Goddard web sites are available on the World Wide
Web at: http://www.gsfc.nasa.gov/.
This archive was generated by hypermail 2.1.2 : Thu Nov 07 2002 - 09:03:49 PST