‘Light echoes’ ripple through distant stellar nebula in amazing Hubble video

The Hubble Space Telescope has captured some incredible new footage of what are called 'light echoes', as pulses of light ripple through the nebula surrounding a distant variable star.

6,500 light years away from us, there's a massive star named RS Puppis that regularly dims and brightens on a roughly six-week schedule, putting it in a class of stars called the 'Cepheid variables'. There are many Cepheid variable stars around, both in our galaxy and in other galaxies astronomers have observed, but what sets RS Puppis apart from some of the others is that it's surrounded by a large gaseous nebula. Every time the star flares up to maximum brightness, the pulse of light ripples through the nebula creating echoes of light that we can see here from Earth.

This short video from the ESA/Hubble group shows RS Puppis pulsing and the resulting light echoes:

The video replays several loops of images taken by Hubble in 2010, from March 25th to April 29th. Although the star only creates one echo during this time, other echoes can be seen expanding through the nebula from previous pulses.

The echoes we're all familiar with are created when sound waves reflect off of objects around whatever emitted the sound, and those reflected waves arrive at our ears after the original sound. Similarly, the light from the star's pulses is reflected, or absorbed and re-emitted, by the gases in the nebula, and arrives at Hubble after the light emitted directly from the star is received. So, they really are echoes of light.

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RS Puppis is a pretty spectacular star, even without its four-light-year-wide nebula and light echoes. It's roughly 200 times the size of our sun, so if you dropped it into the centre of our solar system, it would engulf Mercury and Venus, and would only be around 10 million kilometres shy of swallowing the Earth as well. Also, it's incredibly bright — an average of 15,000 times brighter than the sun (and significantly brighter at maximum).

The study of these Cepheid variable stars is important because astronomers use them as something of a 'milestone' for measuring distances in our galaxy and to other galaxies in the observable universe. RS Puppis and its nebula have provided them with one of the most accurate measurements of distance so far, to within a margin of error of just 90 light years, or just over one per cent.

However, beyond its scientific use, the star and nebula are a beautiful example of the wonders of the universe.

(Image and video courtesy: NASA, ESA, G. Bacon (STScI), the Hubble Heritage Team (STScI/AURA)-Hubble/Europe Collaboration, and H. Bond (STScI and Pennsylvania State University)

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