The
unusual PSR J1311-3430 pulsar system with the first millisecond pulsar
discovered solely by its lighthouse-like gamma-ray emissions (magenta).
The record-breaking pulsar system is so compact that it would fit
completely inside our Sun. This schematic representation shows the Sun,
the companion’s orbit, and the companion at its maximum possible size
true to scale; the pulsar has been greatly enlarged in contrast. SDO/AIA
(sun), AEI
Using a new a new data analysis method, a team of scientists
discovered a millisecond pulsar solely via its pulsed gamma radiation.
Pulsars are the compact remnants from explosions of massive stars.
Some of them spin around their own axis hundreds of times per second,
emitting beams of radiation into space. Until now, they could only be
found through their pulsed radio emissions. Now, scientists at the Max
Planck Institute for Gravitational Physics (Albert Einstein
Institute/AEI) in Hanover assisted by the Max Planck Institute for Radio
Astronomy have discovered a millisecond pulsar solely via its pulsed
gamma radiation. A new data analysis method developed by the AEI was
crucial for the success. The pulsar is accompanied by an unusual
sub-stellar partner, which it is vaporizing, hence the name “black
widow”.
Back in 1994, astronomers discovered a source of strong gamma-rays in
the constellation of Centaurus. They suspected that a pulsar was the
origin of the energetic radiation. Now, a team of scientists led by
Holger Pletsch from the Max Planck Institute for Gravitational Physics
(Albert Einstein Institute, AEI) has solved the mystery and identified
the culprit: the millisecond gamma-ray pulsar PSR J1311-3430. The
development of a new data analysis method by the AEI scientists enabled
the discovery, since rapidly spinning pulsars are extremely difficult to
find.
To unambiguously identify a gamma-ray pulsar, astronomers must know
its properties to very high precision. This includes its position, spin
frequency, and how the latter changes over time. If the pulsar is in a
binary system, the analysis problem is even more complicated: at least
three additional orbital parameters have to be determined as well.
In the case of PSR J1311-3430 astronomers had already observed the
companion, which is heated by the radiation from the pulsar, with
optical telescopes. They were thus able to partially constrain the
orbital parameters and confine the position of the pulsar.
A map of the gamma-ray sky as seen by the
Large Area Telescope on board NASA’s Fermi satellite over the course of
four years. The color coding from blue via red to yellow displays the
intensity of the detected gamma radiation from a sector of the sky
measuring 200 by 100 Moon diameters in galactic coordinates. The gamma
radiation from the plane of the Milky Way can be seen as a horizontal
band. The newly discovered radio pulsar J1311-3430 can be clearly seen
as a strong gamma-ray source. AEI
“We developed a particularly efficient method to search the data from
NASA’s Fermi satellite for gamma-ray millisecond pulsars, including
those in binary systems. Only this method enabled us to probe the wide
parameter ranges,” says Holger Pletsch, lead author of the article
published in Science.
The new analysis method enables scientists to conduct a ‘blind search’
for gamma-ray millisecond pulsars for the first time – right up to very
high spinning frequencies.
The scientists analyzed the Fermi data on the Atlas computer cluster
at the AEI. “Our search used data collected by the gamma-ray satellite
over a total of four years. Very soon after we started running the
analysis, a clear signal showed up in the results. What we saw was very
exciting,” says Pletsch.
PSR J1311-3430 spins 390 times per second, emitting gamma-ray photons
into space in the form of a beam, similar to a lighthouse. In roughly
one in a million revolutions of the pulsar, a single photon reaches the
detector on board Fermi.
The gamma-ray signal also reveals much about the companion to the
astronomers: the orbital motion of the binary system modulates the
photon arrival times, yielding information about the partner star. “The
companion object is small and unusually dense,” says AEI Director Bruce
Allen. “It is at least eight times as massive as the planet Jupiter, but
has at most 60 percent the planet’s radius.”
From this information, the researchers calculated the density of the
companion, which turned out to be unusually high; it is around 30 times
as dense as the Sun. Presumably, the small companion is the compact
remnant of a star which has been orbiting the pulsar since earlier
times. Over time, the pulsar accreted matter from the star, thereby
accelerating its rotation. Pulsar and companion moved closer and closer
together.
“At present, the remaining stellar core, which presumably consists
mainly of helium, is heated by the radiation from the pulsar and
literally evaporated,” says Holger Pletsch. Astronomers call this type
of pulsar a ‘black widow’, in analogy with a species of spider which
kills the smaller male after mating. In the distant future, PSR
J1311-4330 might possibly completely vaporize its companion and from
then on travel through space alone.
And that’s not all: “Our discovery is not only a first, it also sets
several new records,” explains Bruce Allen. Currently, the odd couple is
orbiting its common center of mass on an almost perfect circular
trajectory in only 93 minutes. This is the shortest known orbital period
of all pulsars in binary systems.
This computer graphic shows the structure of
NASA’s Fermi satellite. The central, box-shaped instrumentation platform
lies between the solar panels. The Large Area Telescope, whose data the
astronomers evaluated, is hidden beneath the black cover visible on the
top. NASA
At a distance of only 1.4 Earth-Moon separations, the binary system
is the closest one known to date with a pulsar. The pulsar is speeding
along its circular orbit with at least 13,000 kilometers per hour. Its
light-weight companion is even faster, at up to 2.8 million kilometers
per hour.
Holger Pletsch and his colleagues also had a close look at older
observations with the Green Bank radio telescope in West Virginia, but
were unable to find the fast pulsar here. “Apparently, the cloud of
vaporized material from the companion absorbs most of the radio wave
emissions from the pulsar and possibly makes it invisible to radio
telescopes,” says Lucas Guillemot from the Max Planck Institute for
Radio Astronomy in Bonn, co-author of the publication. The scientists
are already planning further observations at higher radio frequencies.
They hope to use them to accurately determine the object’s distance from
Earth, for example.
Systems like this provide astronomers with new insights into the
evolution of very close binary systems, which are as yet still
incompletely understood. PSR J1311-3430 could also shed new light on the
generation of the gamma-ray photons and radio emissions in the strong
magnetic field of pulsars. The pulsar may just be the tip of the
iceberg: many other unidentified gamma-ray sources may harbor similarly
unusual systems. Thirty years after the discovery of the first
millisecond pulsar in the radio range, the novel analysis method of the
Max Planck researchers at the AEI has opened a new door to the easier
identification of these elusive celestial objects.
10/27/2012 10:15:41 AM
A primary critique
of technoscience is that it targets a 'straw man' construction of
science. That is, contemporary philosophy of science typically takes a
pragmatic and instrumental view of objectivity. From this perspective,
what is objective is what can be measured, transfers to other contexts,
and can be used to make predictions. This is not different from the
performative view of objectivity preferred by technoscience, leaving
technoscience with a critique of a naive view of science that many, if
not most, contemporary scientists would not agree with.
The concept of material networks is also
ontologically unclear and somewhat
archaic, depending upon a material/ideal
dichotomy that has largely been abandoned, by both scientists and philosophers, during the latter half of the twentieth century.
Finally, the boundaries separating traditional scientific areas have
also been increasingly blurred in scientific practice during the course
of the twentieth century, with many knowledge fields now being
fundamentally trans-disciplinary. Many traditional areas of science,
such as biology, zoology and botany, have been superseded by more
systemic conceptions, such as eco-sciences and approaches that integrate
older conceptions of nature with conceptions in which relationships
between human activity (production, economics, politics, etc.) and
non-human biology are in focus. Today, multi-disciplinary approaches are
often a condition for research funding.
These considerations question the current relevance of technoscience,
seeing its critique as belonging perhaps to a 1970s view of science,
its philosophical foundations having been superseded by
post-structuralism, and its vision as merely descriptive of what most contemporary scientists and technologists take for granted.
10/26/2012 12:39:30 PM
We look at the
concept of technoscience by considering three levels: a
descriptive-analytic level, a deconstructivist level, and a visionary
level.
On a descriptive-analytic level, technoscientific
studies examine the decisive role of science and technology in how
knowledge is being developed. What is the role played by large research
labs in which experiments on organisms are undertaken, when it comes to a
certain way of looking at the things surrounding us? To what extent do
such investigations, experiments and insights shape the view on
‘nature’, and on ‘our’ bodies? How do these insights link to the concept
of living organisms as
biofacts? To what extent do such insights inform technological
innovation? Can the laboratory be understood as a metaphor for social structures in their entirety?
On a deconstructive level, theoretical work is being undertaken on technoscience to address scientific practices critically, e.g. by
Bruno Latour (
Sociology), by
Donna Haraway (
History of science), and by
Karen Barad (
Theoretical physics).
It is pointed out that scientific descriptions may be only allegedly
objective; that descriptions are of a performative character, and that
there are ways to de-mystify them. Likewise, new forms of
representing those involved in research are being sought.
On a visionary level, the concept of technoscience
comprises a number of social, literary, artistic and material
technologies from western cultures in the third millennium. This is
undertaken in order to focus on the interplay of hitherto separated
areas and to question traditional boundary-drawing: this concerns the
boundaries drawn between scientific disciplines as well as those
commonly upheld for instance between research, technology, the arts and
politics. One aim is to broaden the term ‘
technology’ (which by the Greek etymology of ‘
techné’
connotes all of the following: arts, handicraft, and skill) so as to
negotiate possibilities of participation in the production of
knowledge
and to reflect on strategic alliances. Technoscience can be juxtaposed
with a number of other innovative interdisciplinary areas of scholarship
which have surfaced in these recent years such as
technoetic,
technoethics and
technocriticism.
