The donor star can potentially be either a helium ( or possibly hybrid ) white dwarf, a low-mass helium star, or an evolved main-sequence star.
12.
Christina Th�ne's group prefers a more conventional supernova mechanism, involving a merger between a helium star and a neutron star at a distance of about 5.5 billion light years from Earth.
13.
A helium star is more expanded than a white dwarf, and when gravitational radiation brings the two stars into contact, it is the helium star which will fill its Roche lobe and start mass transfer, at an orbital period of roughly 10 minutes.
14.
A helium star is more expanded than a white dwarf, and when gravitational radiation brings the two stars into contact, it is the helium star which will fill its Roche lobe and start mass transfer, at an orbital period of roughly 10 minutes.
15.
AM CVn stars with a "'helium-star donor "'are formed in a similar way, but in this case the giant that causes the common envelope is more massive and produces a helium star rather than a second white dwarf.
16.
Telescopium hosts two unusual stars with very little hydrogen that are likely to be the result of two merged white dwarfs : PV Telescopii, also known as HD 168476, is a hot blue extreme helium star, while RS Telescopii is an R Coronae Borealis variable.
17.
Those orange stars found to have a higher than usual concentration of lithium ( such as Centaurus X-4 ) orbit massive objects neutron stars or black holes whose gravity evidently pulls heavier lithium to the surface of a hydrogen-helium star, causing more lithium to be observed.
18.
A " helium star " is also a term for a hypothetical star that could occur if two helium white dwarfs with a combined mass of at least 0.5 solar masses merge and subsequently start nuclear fusion of helium, with a lifetime of a few hundred million years.
19.
Space-based detectors like LISA should detect objects such as binaries consisting of two white dwarfs, and AM CVn stars ( a white dwarf accreting matter from its binary partner, a low-mass helium star ), and also observe the mergers of supermassive black holes and the inspiral of smaller objects ( between one and a thousand solar masses ) into such black holes.
20.
He is the author of " Elements of the Orbit of Reid's Comet " ( University of Toronto, 1922 ), " The Minimum Masses of Three Spectroscopic Binary Stars " ( J . O . Patenaude, 1932 ), and " The Spectroscopic Orbits of the Four Helium Stars H . D . 29376, H . D . 39698, H . D . 44701 and H . D . 208095.
