Credit: X-ray: NASA/CXC/ICE/A.Papitto et al
These two images from NASA's Chandra X-ray Observatory show a large change in X-ray brightness of a rapidly rotating neutron star, or pulsar, between 2006 and 2013. The neutron star - the extremely dense remnant left behind by a supernova - is in a tight orbit around a low mass star. This binary star system, IGR J18245-2452 (mouse over the image for its location) is a member of the globular cluster M28.
As described in a press release from the European Space Agency, IGR J18245-2452 provides important information about the evolution of pulsars in binary systems. Pulses of radio waves have been observed from the neutron star as it makes a complete rotation every 3.93 milliseconds (an astonishing rate of 254 times every second), identifying it as a "millisecond pulsar."
Credit: X-ray: NASA/CXC/ICE/A.Papitto et al
The widely accepted model for the evolution of these objects is that matter is pulled from the companion star onto the surface of the neutron star via a disk surrounding it. During this so-called accretion phase, the system is described as a low-mass X-ray binary because bright X-ray emission from the disk is observed. Spinning material in the disk falls onto the neutron star, increasing its rotation rate. The transfer of matter eventually slows down and the remaining material is swept away by the whirling magnetic field of the neutron star as a millisecond radio pulsar forms.
The complete evolution of a low-mass X-ray binary into a millisecond
pulsar should happen over several billion years, but in the course of
this evolution, the system might switch rapidly between these two
states. The source IGR J18245-2452 provides the first direct evidence
for such drastic changes in behavior. In observations from July 2002 to
May 2013 there are periods when it acts like an X-ray binary and the
radio pulses disappear, and there are times when it switches off as an
X-ray binary and the radio pulses turn on.
The latest observations with both X-ray and radio telescopes show
that the transitions between an X-ray binary and a radio pulsar can take
place in both directions and on a time scale that is shorter than
expected, maybe only a few days. They also provide powerful evidence for
an evolutionary link between X-ray binaries and radio millisecond
pulsars.
The X-ray observations contained data from Chandra, ESA's XMM-Newton,
the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) and
NASA's Swift/XRT and the radio observations used the Australia Telescope
Compact Array, the Green Bank Telescope, Parkes radio telescope and the
Westerbok Synthesis Radio Telescope.
The observations of IGR J18245-2452 and their implications are described in a paper published in the September 26th, 2013 issue of Nature.
The first author is Alessandro Papitto from the Institute of Space
Sciences in Barcelona, Spain. The co-authors are C. Ferrigno and E.
Bozzo from Université de Genève, Versoix, Switzerland; N. Rea from the
Institute of Space Sciences in Barcelona, Spain; L. Pavan from
Université de Genève, Versoix, Switzerland; L. Burderi from Universit´a
di Cagliari, Monserrato, Italy; M. Burgay from INAF-Osservatorio
Astronomico di Cagliari, Capoterra, Italy; S. Campana from
INAF-Osservatorio Astronomico di Brera, Lecco, Italy; T. Di Salvo from
Universit´a di Palermo, Palermo, Italy; M. Falanga from International
Space Science Institute, Bern, Switzerland; M. Filipovi´c from
University of Western Sydney, Penrith, Australia; P. Freire from
Max-Planck-Institut f´ur Radioastronomie, Bonn, Germany; J. Hessels from
Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands;
A. Possenti from INAF-Osservatorio Astronomico di Cagliari, Capoterra,
Italy; S. Ransom from National Radio Astronomy Observatory,
Charlottesville, VA; A. Riggio from Universit´a di Cagliari, Monserrato,
Italy; P. Romano from INAF-Istituto di Astrosica Spaziale e Fisica
Cosmica, Palermo, Italy; J. Sarkissian from CSIRO Astronomy and Space
Science, Epping, Australia; I. Stairs from University of British
Columbia, Vancouver, Canada; L. Stella from INAF-Osservatorio
Astronomico di Roma, Roma, Italy; D. Torres from the Institute of Space
Sciences in Barcelona, Spain; M. Wieringa from CSIRO Astronomy and Space
Science, Narrabri, Australia and G. Wong from University of Western
Sydney, Penrith, Australia.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the
Chandra Program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory controls Chandra's science and
flight operations from Cambridge, Mass.
Fast Facts for IGR J18245-2452:
Scale: Each panel is 1.2 arcmin across (About 6 light years)
Category: Neutron Stars/X-ray Binaries
Coordinates (J2000): RA 18h 24m 32.00s | Dec -24° 52' 10.70"
Constellation: Sagittarius
Observation Date: 30 May 2006 and 29 Apr 2013
Observation Time: 26 (1 day, 2 hours).
Obs. ID: 6769, 15645 I
Instrument: ACIS
References: Papitto, A. et al, 2013, Nature (accepted); arXiv:1305.3884
Color Code: X-ray: Blue
Distance Estimate: 18,000 light years
