Stellar Collision Survivor is New Kind of Rare Pulsating Star

Stars can collide in a fantastic display, creating survivor remnants that can then be later detected and examined by astronomers. Now, researchers have discovered the brightness of a specific remnant varies in a way not seen before on this type of rare star. Their findings could reveal exactly what happens when stars collide.

Stars like our sun expand and cool to eventually become red giant stars when the hydrogen that fuels their cores begins to run out. These expanding red giants will sometimes collide with an orbiting companion star, smashing into it as it continues to grow. During these collisions, as much as 90 percent of the red giant star's mass can be stripped off, leaving it a shell of its former self. Despite knowing this, though, stellar collisions have largely remained a mystery. In fact, only a few stars that have recently emerged from a stellar collision are known, which means that it's been difficult to study the connection between stellar collisions and the various exotic stellar systems that they produce.

Now, scientists may have learned a little bit more with these recent observations. An eclipsing binary system containing the remnants of a star collision recently showed up in a search for extrasolar planets. Using a high-speed camera, the astronomers then studied the eclipses of the star in detail. They found that the remnant of the stripped red giant has turned into a new type of pulsating star.

What does that mean exactly? Many stars, including our own sun, vary in brightness due to pulsations caused by sound waves bounding around inside the star. For the new variable star, each pulsation cycle takes about five minutes and can be used to study the properties of the star below its visible surface.

"We have been able to find out a lot about these stars, such as how much they weigh, because they are in a binary system," said Pierre Maxted from Keel University in a news release. "This will really help us to interpret the pulsation signal and so figure out how these stars survived the collision and what will become of them over the next few billion years."

The findings have allowed researchers to better understand this new pulsating star. Currently, the astronomers are planning on working out how long it will be before the star starts to cool and fade to produce a stellar corpse, known as a white dwarf, of abnormally low mass.

The findings are published in the journal Nature.