SSN 7 is a so-called contact binary located in the Small Magellanic Cloud, a dwarf galaxy some 210,000 light-years away in the constellation of Tucana. Also known as MPG 435, this binary system is a member of the very young stellar cluster NGC 346.
The stars in the SSN 7 binary system are in partial contact and swapping material with each other, with one star currently feeding off the other.
They orbit each other every 3 days and are the most massive touching stars (known as contact binaries) yet observed.
Comparing the results of their observations with theoretical models of binary stars’ evolution, they found that, in the best-fit model, the star that is currently being fed on will become a black hole and will feed on its companion star. The surviving star will become a black hole shortly after.
These black holes will form in only a couple of million years, but will then orbit each other for billions of years before colliding with such force that they will generate gravitational waves that could theoretically be detected with instruments on Earth.
“Thanks to gravitational wave detectors Virgo and LIGO, dozens of black hole mergers have been detected in the last few years,” said University College London Ph.D. student Matthew Rickard.
“But so far we have yet to observe stars that are predicted to collapse into black holes of this size and merge in a time scale shorter than or even broadly comparable to the age of the Universe.”
“Our best-fit model suggests these stars will merge as black holes in 18 billion years.”
“Finding stars on this evolutionary pathway so close to our Milky Way Galaxy presents us with an excellent opportunity learn even more about how these black hole binaries form.”
“This binary star is the most massive contact binary observed so far,” added University of Potsdam Ph.D. student Daniel Pauli.
“The smaller, brighter, hotter star, 32 times the mass of the Sun, is currently losing mass to its bigger companion,…
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