V is For Valentine… V838

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And the V we’re taking a stereo look at on Valentine’s Day is V838 Monocerotis – an unusual “light echo” from a variable star. If you’re curious to know more about what you’re looking at, then prepare to take a 20,000 light year journey across space and step inside…

Like all our our “stereo” image produced for UT by Jukka Metsavainio, two versions are presented here. The one above is parallel vision – where you relax your eyes and when you are a certain distance from the monitor screen the two images will merge into one to produce a 3D version. The second – which appears below – is crossed vision. This is for those who have better success crossing their eyes to form a third, central image where the dimensional effect occurs. Jukka’s visualizations of what Hubble images would look like if we were able to see them in dimension come from studying the object, its known field star distances and the different wavelengths of light. Are you ready to “cross” the boundary? Then let’s rock…

When you’re ready to come back to your seat, let’s talk just a little bit about what V838 Monocerotis is and what we currently know about it.

The primary source of light that you’re seeing in here comes from a variable star – the 838th variable star discovered in the constellation of Monocerotis – which underwent a very strange reaction early in 2002. At first astronomers believed it to be a pretty normal nova event, but it didn’t take long to realize this was something altogether different than anything they’d ever witnessed.

When it first began to brighten on January 10, 2002, the light curve measurements began. These graphs show the intensity of light as a function of time – and they came back as ordinary… a white dwarf shedding accumulated hydrogen gas from its binary neighbor. By February 6th, it had reached its maximum visual brightness and started to dim again, just as expected – but only weeks later the infrared wavelength began to do some very strange things – it brightened unexpectedly and did it again just a few more weeks later! This was something astronomers had simply never witnessed…

According to Howard Bond; “Some classes of stars, including novae and supernovae, undergo explosive outbursts that eject stellar material into space. In 2002, the previously unknown variable star V838 Monocerotis brightened suddenly by a factor of ~104. Unlike a supernova or nova, it did not explosively eject its outer layers; rather, it simply expanded to become a cool supergiant with a moderate-velocity stellar wind. Superluminal light echoes were discovered as light from the outburst propagated into the surrounding, pre-existing circumstellar dust. At its maximum brightness (it) was temporarily the brightest star in the Milky Way. The presence of the circumstellar dust implies that previous eruptions have occurred, and spectra show it to be a binary system. When combined with the high luminosity and unusual outburst behaviour, these characteristics indicate that V838 Mon represents a hitherto unknown type of stellar outburst, for which we have no completely satisfactory physical explanation.”

At the time, V838 expanded in size to the point where it would have filled our solar system to the size of Jupiter’s orbit and output a million times the luminosity of our own Sun – changes that happened in an abnormal time span of just months. Since science did have pre-eruption photographs, V838 was thought to be an under luminous F-type dwarf – much like Sol – which deepened the mystery even further. Just what could cause it to go against the laws of thermodynamics?

According to R. Tylenda; “The eruption phase, which lasted till mid-April 2002, resulted from a very strong energy burst, which presumably took place in last days of January at the base of the stellar envelope inflated in pre-eruption. The burst produced an energy wave, which was observed as a strong luminosity flash in the beginning of February, followed by a strong mass outflow in form of two shells, which was observed as an expanding photosphere in later epochs. In mid-April, when the outflow became optically transparent and most of its energy radiated away, the object entered the decline phase during which V838 Mon was evolving along the Hayashi track. This we interpret as an evidence that the main energy source during decline was due to gravitational contraction of the object envelope inflated in eruption. Late in 2002 a dust formation started in the expanding shells which gave rise to a strong infrared excess observed in 2003.”

Since then we’ve learned the V838 eruptive star may have just been entering the main sequence at the time, and we also know it has a B-type companion that’s also just come aboard the main sequence train. This type of information doesn’t add up to a nova event which occurs to older, white dwarfs… even though it may be something we don’t yet understand. It’s possible that V838 Monocerotis may be a post-asymptotic giant branch star – about to end – but again, it doesn’t fit the spectral patterns. According to some evidence, V838 Monocerotis may be a very massive supergiant that experience “carbon flash”… making their way towards the Wolf-Rayet star end of the chapter. It’s possible that the event could have been a “mergeburst” – where a main sequence and pre-main sequence star combined forces – or even a planetary captured event which triggered deuterium fusion.

And maybe we’ll never know in our lifetimes…

No matter if we understand precisely what created it or not, we can still enjoy the wonderful “light echo” produced by V838 Monocerotis, imaged by the Hubble Telescope and visualized for dimension by Jukka. He understands how the light reflects from clouds of interstellar matter between the star and point of the observer. He knows which wavelengths arrived into the camera lens first and which arrived last…

And we’re grateful to have the chance to look straight into the “heart” of this unusual phenomena!

My many thanks once again to Jukka Metsavainio of Northern Galactic for his artistry and we look forward to the next installment!