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Hubble Chronicles Mysterious Outburst
An eruptive star that brightened to 600,000 times its initial intensity and briefly outshone all others in the Milky Way Galaxy has astronomers amazed and puzzled over what happened...The star, named V838 Monocerotis, has suddenly grown so big that if placed in the center of our solar system it would engulf Jupiter.
While I was RTFA, I pretty much expected that this "sudden" event would be revealed as sudden only when measured in geologic or cosmic time; say, a few thousand millenia or so. The fact that this happened over only a few months is fascinating.
This event goes contrary to everything what is known about the star life cycle so far.
New physics just for this star? I doubt it.
One reasonable suggestion without reaching for mysterious new physics is that it is part of a binary system, with a compact object (neutron star, white dwarf or possibly black hole) in a highly eccentric orbit around this main sequence star.
Every x number of years, the compact object skids in on its highly eccentric orbit, and slams through the upper layers of the visible star. Material falls onto compact object, flares up and heats the outer layer of the main sequence star, compact object whizzes out again and is not seen again for another few hundred years or so. The fraction of total mass ejected from the main star is miniscule, so this process does not significantly alter the main star's evolution on the timescale of a few million years, hence the repeated shells of dust seen in these light echoes.
Binary systems of this types have been known about for quite a while (well, on the order of 20 years). The trick is looking for the signature of the compact object, which is a difficult detection.
Dr Fish
1. If the star is moving at a certain velocity, then the average velocity of a particle in a cast-off shell of dust will be at the star's velocity. In other words, the star will stay centered in any spherical shell of material it gives off (yes, I know, some neutron stars get kicked out of their nebulae, but that's a far more energetic process). An interstellar wind, if present, would destroy the spherical shape of the nebula.
2. The nebula is acting as a reflector, no doubt, but it is so thin that the star is perfectly visible through it anyway. It's the red star in the photo(s).
3. The only way this could "magnify the apparent brightness" of the star is if the star and nebula were not resolvable as separate objects. Then light reflected from the nebula could be mistaken as light from the star (ignoring spectral techniques). But the photo is of a fully resolved nebula and star. A child could distinguish light from the star vs. reflected light from the nebula.
"I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
I was with Mark (Wagner) and Sumner (Starrfield) when we got the spectra. . .now I'm going to be really pissed if I'm not on the paper since I was the one taking the spectra. . .
But anyhow. . .the spectra is really interesting, there are P Cygni profiles for every emission line in the spectra (P Cygni's look like half a gaussian in emission with a sharp cutoff to be half a gaussian in absorption). This object was actually noticed by people looking at variable stars and then was picked up by some other folks in Arizona which showed the light echos even in the relatively low resolution images we got on the ground compared to our HST ACS images.