Astronomy Picture of the Day |
APOD: 1998 November 28 - A Lonely Neutron Star
Explanation:
How massive can a star get without imploding into a black hole?
These limits are being tested by the discovery of a lone
neutron star in space.
Observations by the Hubble Space Telescope
have been combined with previous observations by the
X-ray
ROSAT observatory and
ultraviolet
EUVE
observatory for the isolated star at the location of the arrow.
Astronomers are able to directly infer the star's size from
measurements of its unblended brightness, temperature, and an upper
limit on the distance.
Assuming that the object is a
neutron star of typical mass,
some previous theories of neutron star structure would have predicted
an implosion that would have
created a black hole.
That this neutron star
even exists therefore allows a window to the extreme
conditions that exist in the interiors of neutron stars.
APOD: 1998 April 25 - Supernova Remnant and Neutron Star
Explanation:
A massive star ends life as a supernova, blasting
its outer layers back to interstellar space.
The spectacular death explosion is
initiated by the collapse of what has become an impossibly dense
stellar core.
However, this core is not necessarily destroyed. Instead, it may be
transformed into an exotic object with the density of an
atomic nucleus but more total mass
than the sun -
a neutron star.
A neutron star is hard to detect directly because it is
small (roughly 10 miles in diameter)
and therefore dim, but newly formed in this violent crucible
it is intensely hot,
glowing in X-rays.
These
X-ray images from the orbiting ROSAT observatory may offer a premier
view of such a recently formed neutron stars' X-ray glow.
Pictured is the supernova
remnant Puppis A, one of the brightest
sources in the X-ray sky,
with shocked gas clouds still expanding and
radiating X-rays. In the inset close-up view,
a faint pinpoint source of X-rays is visible which is most likely
the young neutron star,
kicked out by the asymmetric explosion and
moving away from the site of the original supernova at about 600 miles
per second.
APOD: 1998 July 23 - X-Ray Pulsar
Explanation:
This dramatic artist's vision shows a
city-sized
neutron star
centered in a disk of hot plasma drawn from
its enfeebled red companion star.
Ravenously
accreting material from the disk,
the neutron star spins faster and faster
emitting powerful particle beams and pulses
of X-rays as it rotates 400 times a second.
Could such a bizarre and inhospitable star system really exist in
our Universe?
Based on data from the orbiting
Rossi X-Ray Timing Explorer (RXTE)
satellite, research teams have
recently announced a discovery which fits
this exotic scenario well - a "millisecond" X-ray pulsar.
The newly detected celestial X-ray beacon
has the unassuming catalog
designation of SAX J1808.4-3658 and is located a comforting
12,000 light years away in the
constellation Sagittarius.
Its X-ray pulses offer evidence of rapid,
accretion powered rotation
and provide a much sought after
connection between
known types of radio and X-ray
pulsars and the
evolution
and ultimate demise of
binary star systems.
Authors & editors:
Robert
Nemiroff
(MTU)
& Jerry Bonnell (USRA)
NASA Technical Rep.:
Jay Norris.
Specific rights apply.
A service of:
LHEA at
NASA/
GSFC
&
Michigan Tech. U.