Sep 4th 2018

Supernovas Steal the Spotlight, but Companion Stars Are the Real Thieves

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Pop quiz: how are supernovas formed? Even though supernovas are often talked about in pop culture, we still don’t have a lot of information about these extravagant stars. Many stars slowly fade away, but in some cases, they die in dramatic and violent cosmic explosions called supernovas (or supernovae) that hurl matter into space at up to 25,000 miles per second, according to National Geographic. It’s no wonder that this astonishing natural phenomenon has served as creative fodder for movies like “Supernova” or songs like “Champagne Supernova” by Oasis.

A supernova can occur when a single star runs out of nuclear fuel and the star compresses itself until the core collapses, resulting in a giant explosion, according to NASA. But new images captured by the Hubble Space Telescope support the idea that some supernovas are formed instead by double-star systems in which one star steals matter from a nearby star, essentially cannibalizing its neighbor, said NASA.

How to Find a Supernova and Companion Star

If you look up at the night sky, the stars appear to be still because most changes occur over extremely long timescales, according to Blake Bullock, director of Civil Air and Space at Northrop Grumman.

Bullock studied astronomy and astrophysics at Wesleyan University and University of California, Berkeley. She also worked for NASA before coming to Northrop Grumman, so she has spent plenty of time gazing up at the stars.

Bullock said, “Astronomy typically doesn’t have a lot of change … Things change over very, very long timescales. Galaxies evolve over millions and hundreds of millions, sometimes billions, of years, but a supernova is a rare, action-packed short-term event.”

A supernova produces a flash of light in the sky that looks like a new star suddenly appearing. As the brightness from the explosion decreases over time, astronomers can use ground-based telescopes and space telescopes to observe the changes and extrapolate information about the star’s physics, said Bullock.

Astronomers witnessed a supernova 17 years ago, and they used the dead star’s location to pinpoint and photograph the surviving companion star. According to an announcement by NASA, these new images support previous space discoveries and provide the most compelling evidence so far that some supernovas originate in double-star systems.

What About Companion Stars?

The supernova that was recently photographed by Hubble, called SN 2001ig, is categorized as a Type IIb stripped-envelope supernova. According to NASA, “Scientists determined that the companion star had siphoned off almost all of the hydrogen from the other star’s stellar envelope … the companion’s thievery created an instability in the primary star, causing it to episodically blow off a cocoon and shells of hydrogen gas before the catastrophe.”

For all the excitement about supernovas, you would think we should know more information about how they occur. While the case of a gravitational collapse is fairly straightforward, double-star system supernovas are still quite mysterious. When a companion star remains, it could stabilize, collapse, turn into a dwarf or even become a black hole. It all depends on the star’s mass and life stage, explained Bullock.

Eyes in the Sky

Why don’t we know more about supernovas and their companion stars? They are rare, and we can only see a small portion of the universe. Hubble captured outstanding images, but the James Webb Space Telescope will be able to see farther and capture the stars that are so far away, and moving at such a velocity, that we perceive them as infrared instead of visible light. This means we’ll be able to make new space discoveries and observe more supernovas and capture images of their companion stars.

Bullock explained that due to the expansion of the universe, the most distant stars are in that category: they’re moving away from each other at such a velocity that we perceive their light as being infrared, or frequencies outside of the visible portion of the electromagnetic spectrum. She added: “There are things that are invisible to us. Webb will unveil a totally different view of the sky that’s just not possible to view otherwise.”

As scientific instruments improve, and our view of the stars improves, we should soon be able to better answer the question: how are supernovas formed?

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