# PSR J1930-1852: a pulsar in the widest known orbit around another neutron star

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PSR J1930-1852: a pulsar in the widest known orbit around another neutron star

http://arxiv.org/abs/1503.06276

(Submitted on 21 Mar 2015)

Quote:
In the summer of 2012, during a Pulsar Search Collaboratory workshop, two high-school students discovered J1930$-$1852, a pulsar in a double neutron star (DNS) system. Most DNS systems are characterized by short orbital periods, rapid spin periods and eccentric orbits. However, J1930$-$1852 has the longest spin period ($P_{\rm spin}\sim$185 ms) and orbital period ($P_{\rm b}\sim$45 days) yet measured among known, recycled pulsars in DNS systems, implying a shorter than average and/or inefficient recycling period before its companion went supernova. We measure the relativistic advance of periastron for J1930$-$1852, $\dot{\omega}=0.00078$(4) deg/yr, which implies a total mass (M$_{\rm{tot}}=2.59$(4) M$_{\odot}$) consistent with other DNS systems. The $2\sigma$ constraints on M$_{\rm{tot}}$ place limits on the pulsar and companion masses ($m_{\rm p}1.30$ M$_{\odot}$ respectively). J1930$-$1852's spin and orbital parameters challenge current DNS population models and make J1930$-$1852 an important system for further investigation.

Mike Hewson
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### PSR J1930-1852: a pulsar in the widest known orbit around anothe

That's a really interesting article. I learnt alot from it at least. Quite well written and imagine the hoot to be one of the students involved in this. I'd reckon there's a good chance they will be thinking of an astronomy career. So the "... aims to interest high-school students in science, technology, engineering and mathematics (STEM) related career path ..." has succeeded well here.

I remember going to a week long summer school in physics at a Melbourne university when in senior high school. We had lots of talks/lectures and demos. I especially remember a guy showing us the mathematics of magneto-hydrodynamics AND urging us not to panic at what we saw. Gasp! I think I dreamt of all those nablas without a clue of what they meant. He emphasised the mathematical modelling nature of physical theory and how one aims to compare & correlate specific prediction with good measurements. I wound up going to a another university but that time greatly encouraged me to do a Science degree.

Thank you for finding and showing this to us. :-)

Cheers, Mike.

( edit ) Also of note is their usage of the phrases 'iron core collapse supernovae' and 'electron capture supernovae' which it appears is replacing the older ( more confusing ) classification of Types I + II with subtypes. So what was called Type Ia is the white dwarfs that over-accreted from a companion and ran out of electron degeneracy pressure ( electrons captured by protons to form neutrons ). Whereas Type Ib, Ic and II are various massive stars ( with different outer envelopes ) that run out of fusion options in the core by reaching iron and thus catastrophically collapsing. That's a much more useful way to think of supernova mechanisms rather than the old with-hydrogen-in-spectrum ( Type II ) and without-hydrogen-in-spectrum ( Type I ) scheme.

( edit ) ( Part of ) the algorithm to determine companion type is quite interesting :

- assume ( Devil's advocate ) that the companion is a main sequence star.

- the Keplerian parameters obtained from the timing gives a minimum companion mass and total system mass. Thus bounding the companion mass.

- use mass/luminosity relationships ( remember the Hertzsprung-Russell diagram ? ) to get an expected spectral type and absolute luminosity.

- use the dispersion modulus to estimate distance.

- calculate the expected apparent luminosity ( inverse square law ).

- calculate the expected angular width of the system from the distance and the Keplerian semi-major axis ie. how wide apart might they appear to be ?

- use well calibrated photometry to image the sky surrounding the best position solution from the 'gridding' radio observations.

- with care make the limiting magnitude of the photometry well below the expected luminosity.

- find no visual source where there should be one if the companion was main sequence.

- thus there is no main sequence companion.

( edit ) Finally, charting the pulsar period/period-derivative and spin-period/eccentricity measurements places it in a 'neither fish nor fowl' category, as it were, compared to others including other DNS systems.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal