Astronomers Bradley Schaefer and graduate student Ashley Pagnotta

The discovery settles decades of questions over the origin of so-called Type 1a supernovas, researchers said.

Astronomers have long suspected moncler jackets that two stars were responsible for the explosion, with one being a white dwarf — a compact, dying star. But scientists weren't sure if both culprits were white dwarf stars that crashed, or consisted of one white dwarf that siphoned off material from a regular companion star. Both scenarios could cause the supernova.

But some of that doubt has been laid to rest. Astronomers Bradley Schaefer and graduate student Ashley Pagnotta, both of Louisiana State University, used a Hubble Space Telescope photo of the supernova SNR 0509-67.5 as a critical clue to determine that two white dwarf stars collaborated to set off the star explosion.

Pagnotta presented the results at the 219th American Astronomical Society meeting in Austin, Texas, Wednesday. The research also is detailed in this week's edition of the journal Nature.

A classic 'eureka' moment'
The discovery occurred last year as the astronomers worked on a proposal to search for a companion star in the debris of SNR 0509-67.5, a supernova remnant about 160,000 light-years away in the nearby Large Magellanic Cloud, a satellite of our own Milky Way. (A light-year is the distance that light can travel in one year — about 6 trillion miles, or 10 trillion kilometers.) But a glance at the Jan. 25, 2011, Astronomy Picture of the Day saved them the trouble.

The photo, which shows the supernova remnant 60% off moncler jackets as a gossamer bubble of red gas about 23 light-years across, was taken by the Hubble Space Telescope.
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"They had taken the image we wanted with a different scientific purpose," Schaefer told Space.com.

They printed the image and used a ruler to estimate the supernova remnant's center, then searched for a companion, but they found no trace of one. The quick and dirty process took only half an hour, but answered the question of several decades.

Schaefer describes it as "the classic 'eureka' moment."

Of course, a more in-depth search was needed to be certain, he added. The spherical supernova remnant exploded from a single source that a companion star would have once orbited. The first step, then, was finding that point.

A deeper look
To calculate the exact center, they needed more than a ruler. The pair used three different measurements to determine the source, and all three gave the same region of space.

If the companion was a white dwarf, the collision between the two would have obliterated both. But a regular, main sequence star should still remain. It would no longer be orbiting the destroyed white dwarf, as the blast would have "blew it away," Schaefer explained.

Schaefer and Pagnotta created an enormous error box, based on worst-case scenarios of the type of star and how far it could travel — and then searched beyond it. The Hubble Space Telescope data they studied included stars 50 times dimmer than the dimmest scenarios modeled.

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Surprisingly, the center of the ring boasted an object with an amorphous shape.

The team's first instinct was that it was simply a background galaxy that happened to be located in the line of sight with the middle.

"An ex-companion would have to be a point source," Schaefer explained.

They are in the middle of taking spectra to confirm that it is simply a coincidence, but Schaefer is confident it will prove to be irrelevant.

"It looks like a background galaxy, and it quacks like a background galaxy, so I think it probably is a background galaxy," he said.
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But this is the only object anywhere near the center, and there are no point sources that would indicate a leftover star.

When nothing is evidence of something
The lack of a remaining companion star is evidence that the explosion that formed SNR 0509-67.5 was not a combination of a white dwarf and a main sequence star, known as a single-degenerative system.

This left astronomers with only one other theory still standing, a so-called double-degenerative system made up of two white dwarf cheap moncler stars that collided.

"For the first time, we have a decisive answer," Schaefer said. "What we have done for 0509 is eliminated all the 0509 single-degenerative models."