Honestly, I’ve never seen anything like this 4-year timelapse from The Hubble Space Telescope. It looks like an incredible explosion fighting against the cosmic pressures of some unseen force. But it’s not an explosion–it’s more like a 20,000-year old echo.
The star above is V838 Monocerotis, or V838 Mon. It’s a variable star that in 2002 suddenly radiated a burst of light 600,000 times more luminous than our Sun. Astronomers thought that V838 Mon may have gone supernova to produce that incredible burst, but after years of observation with the Hubble Telescope, the star still appeared quite intact and unchanged. So, what the timelapse shows above can’t be gases expanding outwards as if the star finally exploded or went into the next stage of its life. In fact, we are seeing the movement of the star’s light itself–a light echo.
A “light echo” is a stellar phenomenon where the light from a star itself reaches us first, followed by the light that had to pass through the gas and dust surrounding the star. This light bounces around in the stellar debris, and therefore it reaches us after the light coming directly from V838 Mon does. In effect what the timelapse above shows is light echoing around the debris near the star, like luminous shock waves through space. It gives the impression that something is expanding because the fastest light from V838 Mon remains constant, but the apparent expansion is only light slogging its way though gaseous obstacles. The debris was already there. It’s as if you could see lightning and the thunder that followed it through the clouds.
Though astronomers are still in the dark on what caused V838 Mon’s luminous eruption in the first place, it’s pretty clear where all that debris creating the echo came from. Astronomer Katie Mack tells me that the debris surrounding the star “is probably stellar wind and atmosphere that got sloughed off the star earlier in its life.”
Even if we never learn the reason for V838 Mon’s mysterious illumination, at least we will have that view.