From The Louisiana State University (US) via Science Alert (US) : “There’s a Binary Star System That May Explode in Your Lifetime”

From The Louisiana State University (US)

via

ScienceAlert

Science Alert (US)

3 OCTOBER 2021
CARLY CASSELLA

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The remnants of a previous stellar explosion, V838 Monocerotis. (The National Aeronautics and Space Agency (US), The European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU),The Hubble Heritage Team (Space Telescope Science Institute (US)/The Association of Universities for Research in Astronomy (AURA)(US))

An ordinary-looking star system, barely visible in the night sky, appears to have a very bright future in store – and if astronomers’ predictions are right, some of us might even be around to see it.

These days, V Sagittae (V Sge) is so faint it’s hard to find up there, even with a mid-sized telescope. But over the next few decades, as it’s sucked into a nearby white dwarf, all of that could change.

Experts at Louisiana State University (LSU) think this pair of celestial underdogs is destined to become the most luminous star in the Milky Way galaxy, brighter even than Sirius, which currently holds the top spot.

At least, that is, for some 60-odd years. As the star and its dwarf companion gradually become one, their merge is set to create the explosion of a lifetime, and it’s just around the corner.

“Around the year 2083, its accretion rate will rise catastrophically, spilling mass at incredibly high rates onto the white dwarf, with this material blazing away,” says astronomical physicist Bradley Schaefer from LSU.

“In the final days of this death-spiral, all of the mass from the companion star will fall onto the white dwarf, creating a supermassive wind from the merging star, appearing as bright as Sirius, possibly even as bright as Venus.”

In fact, the authors think this explosion could end up being the brightest known nova of all-time, nearly as bright as a supernova.

The last time the world experienced something this extreme was just over a century ago, and the V Sge star system is different from this past explosion in more ways than one.

On their own, white dwarfs are merely embers of dying stars, doomed to blaze into invisibility. But when they’re in a binary system with a nearby companion star, like V Sge, they can steal enough fuel from their neighbor to survive, however briefly.

This is similar to but not quite the same as a classic nova, which occurs when the white dwarf’s surface is heated by a nearby star until runaway nuclear fusion is achieved.

Instead, so-called dwarf novae such as V Sge are known as cataclysmic variables or CVs, and they are caused when an ordinary star slowly falls into a white dwarf in a binary orbit.

In the whole galaxy, there are probably more than a million CVs, but astronomers say V Sge is the most extreme we’ve seen so far, roughly a hundred times more luminous than all other known examples.

And that’s probably because of the companion star’s sheer size, which is nearly 4 times bigger than the hungry white dwarf devouring it.

“In all other known CVs the white dwarf is more massive than the orbiting normal star, so V Sge is utterly unique,” says Schaefer.

Measuring V Sge’s brightness in old sky photos archived in Harvard College Observatory, the team has put together a detailed history of the star going all the way back to the 1890s.

Looking over this timeline, it appears V Sge is spiraling into the dwarf star much faster than we thought, moving ever closer towards a mass transfer of matter that will likely be highly explosive.

Because V Sge is so big, the authors calculate almost all of its gas will have to fall into the dwarf star within the last few weeks and days of the merge, driving a stellar wind larger than anything seen before.

“V Sge is exponentially gaining luminosity with a doubling time scale of 89 years,” says astronomer Juhan Frank from LSU.

“This brightening can only result with the rate of mass falling off the normal companion star increasing exponentially, ultimately because the binary orbit is in-spiraling rapidly.”

Given some uncertainty around the final date of this remarkable nova, the team thinks the two stars will merge sometime between 2067 and 2099, which means some of us may actually see it with our own eyes.

“Now people the world over can know that they will see a wondrous guest star shining as the brightest in the sky for a month or so, being pointed at by the Arrow just below Cygnus, the Swan,” says Schaefer.

The findings were presented at the 235th American Astronomical Society meeting.

See the full article here.

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The Louisiana State University is a public research university in Baton Rouge, Louisiana. The university was founded in 1853 in what is now known as Pineville, Louisiana, under the name Louisiana State Seminary of Learning & Military Academy. The current LSU main campus was dedicated in 1926, consists of more than 250 buildings constructed in the style of Italian Renaissance architect Andrea Palladio, and the main campus historic district occupies a 650-acre (2.6 km²) plateau on the banks of the Mississippi River.

Louisiana State University is the flagship school of the state of Louisiana, as well as the flagship institution of the Louisiana State University System, and is the most comprehensive university in Louisiana. In 2017, the university enrolled over 25,000 undergraduate and over 5,000 graduate students in 14 schools and colleges. Several of LSU’s graduate schools, such as the E. J. Ourso College of Business and the Paul M. Hebert Law Center, have received national recognition in their respective fields of study. It is classified among “R1: Doctoral Universities – Very high research activity”. Designated as a land-grant, sea-grant, and space-grant institution, Louisiana State University is also noted for its extensive research facilities, operating some 800 sponsored research projects funded by agencies such as the National Institutes of Health (US), the National Science Foundation (US), the National Endowment for the Humanities (US), and the National Aeronautics and Space Administration (US). Louisiana State University is one of eight universities in the United States with dental, law, veterinary, medical, and Master of Business Administration programs. The Louisiana State University School of Veterinary Medicine is one of only 30 veterinary schools in the country and the only one in Louisiana.

Louisiana State University’s athletics department fields teams in 21 varsity sports (9 men’s, 12 women’s), and is a member of the NCAA (National Collegiate Athletic Association) and the SEC (Southeastern Conference). The university is represented by its mascot, Mike the Tiger.