Neutron stars can be more massive, while black holes are more rare (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Fri, 18 Jan 2008 07:42:39 GMT
Press Relations Office
Cornell University
Ithaca, New York
Contact: Blaine Friedlander
Phone: (607) 254-8093
FOR RELEASE: Jan. 11, 2008
Neutron stars can be more massive, while black holes are more rare,
Arecibo Observatory finds
ITHACA, N.Y. -- Neutron stars and black holes aren't all they've been
thought to be.
In fact, neutron stars can be considerably more massive than previously
believed, and it is more difficult to form black holes, according to new
research developed by using the Arecibo Observatory in Arecibo, Puerto
Rico. Paulo Freire, an astronomer from the observatory, will present his
research at the American Astronomical Society national meeting in Austin
on Jan. 11.
The Arecibo Observatory is managed by Cornell University for the National
Science Foundation.
In the cosmic continuum of dead, remnant stars, the Arecibo astronomers
have increased the mass limit for when neutron stars turn into black
holes.
"The matter at the center of a neutron star is highly incompressible. Our
new measurements of the mass of neutron stars will help nuclear physicists
understand the properties of super-dense matter," said Freire. "It also
means that to form a black hole, more mass is needed than previously
thought. Thus, in our universe, black holes might be more rare and neutron
stars slightly more abundant."
When the cores of massive stars run out of nuclear fuel, their enormous
gravitation then causes their collapse then becomes a supernova. The core,
typically with a mass 1.4 times larger than that of the sun is compressed
into a neutron star. These extreme objects have a radius about 10 to 16
kilometers and a density on the order of a billion tons per cubic
centimeter. Freire says that a neutron star is like one single, giant
atomic nucleus with about 460,000 times the mass of the Earth.
Astronomers had thought the neutron stars needed a maximum mass between
1.6 and 2.5 suns in order to collapse and become black holes. However,
this new research shows that neutron stars remain neutron stars between
the mass of 1.9 and up to possibly 2.7 suns.
"The matter at the center of the neutron stars is the densest in the
universe. It is one to two orders of magnitude denser than matter in the
atomic nucleus. It is so dense we don't know what it is made out of," said
Freire. "For that reason, we have at present no idea of how large or how
massive neutron stars can be."
From June 2001 to March 2007, Freire used Arecibo's "L-wide" receiver(sensitive to radio frequencies from 1100 to 1700 MHz) and the Wide-Band
Arecibo Pulsar Processors -- a very fast spectrometer on the Arecibo
telescope -- to examine a binary pulsar called M5 B, in the globular
cluster M5, which is located in the constellation Serpens. Like a
lighthouse emits light, a pulsar is a strongly magnetized neutron star
that emits large amounts of electromagnetic radiation, usually from its
magnetic pole. As in the case of a lighthouse, distant observers perceive
a sequence of pulsations, which are caused by the rotation of the pulsar.
In the case of M5 B, these radio pulsations arrive at the Earth every 7.95
milliseconds.
These radio pulsations were scanned by the wide-band spectrometers once
every 64 microseconds for 256 spectral channels, and then recorded to a
computer disk, with accurate timing information. The precise arrival time
of the pulses were then used by the astronomers to accurately measure the
orbital motion of M5 B about its companion. This allowed the astronomers
to estimate the mass (1.9 solar masses) of the pulsar.
Astronomers also working on this research are: Maureen van den Berg,
Northwestern University, Evanston, Ill.; Jason W. T. Hessels, Astronomical
Institute "Anton Pannekoek" of the University of Amsterdam in the
Netherlands; and Alex Wolszczan, Pennsylvania State University, State
College, Pa.
Related Information:
* Arecibo Observatory
http://www.naic.edu/
.
- Follow-Ups:
- Prev by Date: ENTROPY and the Direction of Time from the BIG BANG
- Next by Date: Arecibo telescope finds critical ingredients for the soup of life in a galaxy far, far away (Forwarded)
- Previous by thread: ENTROPY and the Direction of Time from the BIG BANG
- Next by thread: Re: Neutron stars can be more massive, while black holes are more rare (Forwarded)
- Index(es):
Relevant Pages
|
