Astronomers Document a Not-So-Supernova in the Milky Way

JAKARTA – Supernovas are not always super. The explosion that marks the death of a star is often very energetic. But once in a while they are completely useless.

Scientists on Wednesday detailed one dud — a massive star that has had most of its material sucked up by the gravitational pull of a companion star in a mating stellar system called a binary system that at the time exploded at the end.

The eventual explosion was so benign that even the collapsing star – now a very dense object called a neutron star – remained in a tame circular orbit with its companion. A more powerful explosion would at least result in a more oval-shaped orbit and could even send the star and its companions hurtling in the opposite direction.

This binary system, studied using telescopes at the Chile-based Cerro Tololo Inter-American Observatory, is located about 11,000 light years from Earth in our Milky Way galaxy towards the constellation Puppis. One light year is the distance light travels in a year, 5.9 trillion miles or 9.5 trillion km.

The mass of a neutron star is about 1.4 times that of our sun, having previously been 12 times as massive as the sun. The companion star has a mass 18 to 19 times greater than the sun after eating its partner. The two stars orbit each other every 59-1/2 days, separated by about eight-tenths the distance that exists between Earth and the sun.

The resulting anemic stellar explosion is called an “ultra-stripped” supernova. This occurs when a massive star collapses from running out of fuel in its core, but cannot withstand the powerful explosion because the companion star has sucked in most of its outer layers and thrown out material that would otherwise be ejected violently into space.

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“Because there is so little material in the stellar envelope, there is almost no ejection of shock during collapse,” said astronomer Noel Richardson of Arizona-based Embry-Riddle Aeronautical University, lead author of the study published in the journal Nature.

Study co-author Clarissa Pavao, an Embry-Riddle undergraduate student studying physics, described the explosion as: “Dark, ethereal, and passive.”

“If there were more explosions, the orbit would not be circular,” said Richardson. “A normal supernova does not necessarily destroy its companion, but it can disturb the orbit even more. It could, for example, kick systems that make orbits much more elliptical or even send surviving stars and their neutron stars on fast trajectories in opposite directions at velocities that could even send them out of the galaxy.”

The types of binary systems studied in this study are rare, with about 10 estimated to exist in the Milky Way, which is home to an estimated 100-400 billion stars.

In contrast to the lonely sun, perhaps half of our galaxy’s stars are in a binary system. Scientists have pondered whether planets capable of hosting life exist in such a system, as depicted, for example, by Luke Skywalker’s “Star Wars” character Tatooine’s home planet.

“We know of several systems that are binary with planets, but these are more difficult to confirm, and all of this is for stars with the mass of our sun,” said Richardson. “In the case of these massive stars, we have yet to detect planets around them. Stars are much heavier and more luminous than sun-like stars, making planet detection more difficult than around smaller stars.”

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