Hubble sees the luminous echo of the red hypergiant

In 2002, a red variable hypergiant temporarily became the brightest star in the Milky Way. Hubble observed this star for several years and saw a unique phenomenon: a luminous echo.

V838 Monocerotis is a binary star located 19,000 light years from Earth. The heavy red star is a real giant. For example, the star has a radius of 1570 solar rays (or 1570 times the radius of the sun). This makes it one of the greatest known stars that we know of.

In January 2002, the hypergiant – which is normally barely visible – quickly became 600,000 times brighter than the sun. A few years earlier there had been a major rash, but it went fairly unnoticed. Scientists suspect that the hypergiant has swallowed a large planet or a small star. Light from the eruption then passed through a cloud of dust surrounding the star. It looks like the V838 Monocerotis is emitting matter, but it isn’t. Here we see the expanding flash illuminating the already existing dust clouds around the star.

Hubble took several photos of V838 Monocerotis in the period from 2002 to 2006, resulting in the following series. Rarely do astronomers see a celestial body change in a short period of time. The photos clearly show how the star’s light travels through the dust clouds. The light emitted first, when the star was hotter, appears bluer. Therefore, the gas plates appear to have blue edges.

The gas fragments in the photo above are several trillions of kilometers long. In the photo on the right, the light echo is six light years in diameter. The luminous echo is therefore wider than the distance from the sun to the nearest star: Proxima Centauri.

When the photos are pasted one after the other in a timelapse, a beautiful video is created. This video is not completely realistic, as the scenes between photos are simulated, but it shows how a star changes in a short period of time.