Hubble Images Variable Star's Light Echo
December 18, 2013

Variable Star’s Light Echo Caught On Video By Hubble Telescope

[ Watch the Video: Light Echoes Around RS Puppis ]

redOrbit Staff & Wire Reports - Your Universe Online

Observations from the NASA/ESA Hubble Space Telescope, collected over the span of five weeks, show the variable star RS Puppis growing alternately brighter and dimmer – a phenomenon known as a light echo.

Hubble monitored RS Puppis, which is ten times more massive and roughly 15,000 times more luminous than the sun, and captured it at different stages throughout its approximately 41-day cycle. The light echo that can be seen around the star makes it look as though gas clouds are expanding outwards from the star.

“For most of its life, a star is pretty stable, slowly consuming the fuel at its core to keep it shining brightly,” NASA explained in a statement Tuesday. “However, once most of the hydrogen that stars use as fuel has been consumed, some stars evolve into very different beasts – pulsating stars. They become unstable, expanding and shrinking over a number of days or weeks and growing brighter and dimmer as they do so.”

RS Puppis, which is located some 6,500 light-years away from Earth, is a type of variable star known as a Cepheid variable. These types of variable stars have comparably long periods, according to NASA. For example, RS Puppis varies in brightness by a factor of five about every 40 days.

However, astronomers explain that RS Puppis is “unusual” for a variable star, as it is surrounded by thick, dark clouds of gas and dust known as a nebula. Hubble monitored the star and its surrounding nebula for five weeks back in 2010, delivering images at various stages of its cycle and used to create a time-lapse video of the object.

“The apparent motion shown in these Hubble observations is an example of a phenomenon known as a light echo,” the agency said. “The dusty environment around RS Puppis enables this effect to be shown with stunning clarity. As the star expands and brightens, we see some of the light after it is reflected from progressively more distant shells of dust and gas surrounding the star, creating the illusion of gas moving outwards.”

According to NASA, that reflected light has to travel a greater distance, and as such arrives here on Earth after light that travels directly from the star to a telescope. The phenomenon is similar to the way in which sound reflects off surrounding objects, causing the person listening to it to detect an audible echo.

“While this effect is certainly striking in itself, there is another important scientific reason to observe Cepheids like RS Puppis,” the agency added. “The period of their pulsations is known to be directly connected to their intrinsic brightness, a property that allows astronomers to use them as cosmic distance markers.”

The light echo surrounding RS Puppis also helped astronomers measure its distance from us a few years ago, allowing them to determine the most accurate measurement to date of a Cepheid's distance. Cepheids are said to be a rare and exceedingly luminous type of star, and studying them can help scientists measure and understand some of the mysteries of the universe, NASA officials added.