We’re going to see a lot more of V Sagittae. One day


Astronomers are excited by a tiny binary star.


Sagitta is a constellation on the edge of the Summer Triangle, defined by the three stars Vega, Deneb and Altair (in Aquila the Eagle).

LSU/Bradley E. Schaefer, Juhan Frank, Manos Chatzopoulos

By Richard A Lovett

A faint star named V Sagittae is poised to become the astronomical object of the century.

But don’t hold your breath, because it’s not expected to happen until 2083, says Bradley Schaefer, an astronomer at Louisiana State University, US.

Though, he said, singling out one of the more youthful members of the press corps at this week’s meeting of the American Astronomical Society in Hawaii, “you’re young enough. Set your calendar!”

Not that doing so might be all that practical, since his current estimate for when the event might occur has an uncertainty of 16 years.

Still, nothing like this has occurred in recent history. “We haven’t had a transient in the sky this bright since Kepler’s supernova of 1604,” Schaefer says.

At the moment, the potential source of all this drama is an “inconspicuous little star”, barely visible with a backyard telescope.

What makes it exciting, though, is that V Sagittae is actually a binary star, in which a small white dwarf is in close orbit around a larger, normal star.

In the process, Schaefer says, the white dwarf is stripping mass away from the normal star.

This causes the white dwarf’s orbit to spiral ever closer to its companion, increasing the rate at which it can steal mass from its companion. “[More] mass is falling onto it, faster and faster.”

By the end of this death spiral, the white dwarf will be gobbling up as much as one or two solar masses of matter over the course of a few weeks.

The result will be the production of an enormous amount of energy – somewhere between the amount released by a nova and a supernova.

Schaefer calls this a merger burst, in order to distinguish it from novas and supernovas, saying that when it occurs, V Sagittae will briefly become the brightest star in the sky, possibly becoming even brighter than the planet Venus.

“[It] will appear as a sudden ‘guest star’, lasting roughly a month, near peak brightness,” he says.

Intriguingly, he adds, it will appear in the constellation Sagitta, which is Latin for arrow. “The arrow will actually be pointing at this star,” he says.

Proof of this prediction comes from archival images of V Sagittae dating back to 1890. “It’s been brightening by a factor of 2.2 from 1900 to 2000,” Schaefer says.

This, he adds, is confirmed by two independent data sources, “both of which show V Sagittae brightening with an unprecedented and fast rate”.

Not that the real proof is likely to occur before 2083. Meanwhile, it’s fun to know that the future might hold surprises worth waiting for.

Contrib ricklovett.jpg?ixlib=rails 2.1
Richard A. Lovett is a Portland, Oregon-based science writer and science fiction author. He is a frequent contributor to COSMOS.
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