We consider a new operation on the family of binary relations on integers called Hadamard star. View a binary relation R ⊆ N × N as a mapping of N into the power set of N and let R(n) denote the subset of integers m such that (n,m) ∈ R. Then the Hadamard star of R is the relation which assigns to each integer n the Kleene star of R(n). This is reminiscent of the Hadamard inverse of series with ...

Many binary star systems are not wide enough to contain the progenitor stars from which they were made. One explanation for this is that when one star becomes a red giant a common envelope forms around both stars in the binary system. The core of the giant and its companion star continue to orbit one another inside the envelope. Frictional energy deposited into the common envelope may lead to i...

Markwardt and Ögelman (1995) used ROSAT to reveal a 12 by 45 arcmin structure in 1 keV X rays around the Vela pulsar, which they interpret as a jet emanating from the pulsar. We here present an alternative view of the nature of this feature, namely that it consists of material from very deep inside the exploding star, close to the mass cut between material that became part of the neutron star a...

Within the next decade, ground based gravitational wave detectors are in principle capable of determining the compact object merger rate per unit volume of the local universe to better than 20% with more than 30 detections. These measurements will constrain our models of stellar, binary, and star cluster evolution in the nearby present-day and ancient universe. We argue that the stellar models ...

It is known that most visible stars are binary: they have a nearby companion star, and these two stars orbit around each other. Based on this fact, until recently, astronomers believed that, in general, most stars are binary. A few years ago, a surprising paper showed that while most bright stars are indeed binary, most dim stars are single. In this paper, we provide a simple qualitative explan...