Here today - gone tommorow ?

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Here today - gone tommorow ?

Post by JohnM »

At the end of June there was an announcement by ESO that a massive star had disappeared without following the normal route of exploding as a supernova (SN).

Two explanations have been proposed one that the star suddenly became less bright perhaps at the end stage of being a Luminous Blue Variable or that the star has collapsed into a black hole without passing through the SN stage. This star was (is ?) located in the Kinman Dwarf galaxy

The ESO press release is at and you can read a pre-print of the paper at ... o2010a.pdf

While a number of articles have said that this is the first discovery of a disappearing star this is not correct a star also disappeared some time between 2007 and 2015. See this URL ... black-hole . This was in NGC 6946, a spiral galaxy 22 million light-years away that is nicknamed the "Fireworks Galaxy" because supernovae frequently happen there

The possibility of a direct collapse of massive holes is supported by some models of the deaths of massive stars but we are into the hand wavy astrophysics territory until more evidence is found. If true this route could provide a source of Black Holes that exist in the mass gap - those are two large to be formed by a SN and two small to be galactic scale black holes. Thanks to the LIGO gravitational wave detections there is now evidence that the mass gap does not exist as several gravitational wave events have involved Black Holes in the mass gap.

It would be really useful to discover a disappearing star in our own galaxy. Most amateurs hunting for SN subtract the latest image from an older reference image so that new objects show up but this does not show stars that have disappeared. To do this one would have to reverse the process but since they are searching for bright objects like SN the disappearance of a star in a distant galaxy would be unlikely to be visible.

It would probably be more productive to take wide field images of the Milky Way and then subtract these but the images need to be deep enough to record dim stars as the likelihood of a faint star disappearing is much higher.

There are a number of professional all (or wide) sky surveys that may be able to capture a disappeared sky but from what I have been able to find the analysis pipelines are not set up to discover missing stars. For instance the Gaia Alerts pipeline is not programmed to flag disappearing stars. It is not clear to me how the main astrometry & photometry pipeline will treat a star that no longer exists - it could be that it will be rejected as an error.

I have not looked at the other wide field surveys yet but what happens will depend on how the pipeline is programmed and the possibility of stars disappearing without going through the SN stage is fairly new.

Anyone want to start their own wide sky survey to try to find a disappearing star in the Milky Way ?

John Murrell
Engineer @ Work - Astronomer @ Play
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