But why?

The answer apparently, is that we haven't the slightest clue.

Spooky........

 

I have a clue. Supernova's. Did their thing and then were extinguished. 

 

Unless aliens were using those Nitecore tactical flashlights and the batteries ran out.

Edited September 25, 20214 yr by martin-w

52 minutes ago, martin-w said:

I have a clue. Supernova's. Did their thing and then were extinguished. 

I don't think supernovas happen often enough for this, and if they did, then there should (probably) be a nebula and a detectable star remnant? (Off the top of my head)

Edited September 25, 20214 yr by HiFlyer

2 hours ago, HiFlyer said:

I don't think supernovas happen often enough for this, and if they did, then there should (probably) be a nebula and a detectable star remnant? (Off the top of my head)

I found this threat by chance with a Google search and registered just to reply.

There is a supernova in a medium-sized galaxy every century or so, and there are at least 100 billion galaxies in the observable Universe. 70 years ago, astronomers could discover about a dozen of them each year, but by now, it's over ten thousand as year.So no, these disappearing stars aren't at all frequent compared to supernovae.

Supernovae do leave a nebula behind, and with the exception of one subtype (Ia, which happens when, one way or another, a smaller burned-out star gains enough mass to surpass the limit of stability), do leave a remnant behind (either a neutron star or a black hole). However, you can detect those only in the nearest galaxies.

We do have ideas of what could cause these disappearances - but, as always in science, we'd need further research to settle for one with greater confidence. Actually, we have multiple ideas, and it is likely that each of these are among the 700. I list some of them, and tell in advance that the second one would be the most interesting.

The simplest possibility is martin-w's suggestion: a supernova that was just not noticed. This could very well happen decades ago: back then, most astronomical telescopes were used to look at a rather small part of the sky for long times, and it was left to amateur astronomers with their much weaker telescopes to constantly monitor the entire sky for transient objects. But nowadays, there are survey telescopes that photograph large parts of the sky regularly.

Another possibility is a so-called "dud supernova". The most common supernovae are explosions of the outer layers of stars with 8 to 15-30 solar masses after the implosion of their burned-out core into a neutron star. Even heavier stars suffer the same implosion-explosion, but leave behind black holes. But calculations long showed that if you increase mass even further, the formation of the black hole can be so rapid that the outer layers of the star are swallowed before the energy transfers could make them explode. There have been already at least two candidates for such dud supernovae, it would be nice to find more and find corroborating evidence. These are so rare, however, that they would only be the likely explanation for disappearances of stars in other galaxies, not in ours.

There are also a host of less fancy possibilities. One is that the star we saw earlier was, in fact, a reflection of the light of an even earlier undetected supernova on a nebulae a few dozen lightyears from the supernova. Another is that the original star was seen in a relatively long-lasting transient state of a different kind: a star merger (when two normal stars spiral into each other or collide, they will form a bigger star with the combined mass, but for a few months to years, this combined star will be boated up and much brighter). Still another possibility is that a normal star got obscured by some object, most likely a dense dust cloud orbiting around it or around a faint companion star.

3 hours ago, martin-w said:

I have a clue. Supernova's. Did their thing and then were extinguished. 

 

Unless aliens were using those Nitecore tactical flashlights and the batteries ran out.

Or, they filled in those holes in the screen.

I know what happened to them.  And there were thousands more of them but we only started counting 70 years ago.

You see, they all had earthlike planes populated with humanoids who got so technologically advanced that they first destroyed the climate and habitat and ecology their own planet and went to neighboring planets and repeated the same behavior.  So the suns got pi**ed off and turn off the switch.

Noel