Astronomers Link 60-Minute Brightening to Large Magellanic Cloud Star Brightening
Astronomers from Swinburne University in Melbourne linked a large magellanic cloud star brightening on 18 December 2019 to gravitational microlensing. The star brightened for about an hour, then returned to normal and was never seen to vary again.
The event matters because the light curve was smooth and symmetrical, a shape that points to a lens passing in front of the star rather than to ordinary stellar variability. The team named the lensing object Phoebe and calculated its mass at approximately three times that of the Moon.
Swinburne University Data
The event appeared in a high cadence survey of the Large Magellanic Cloud, where the short duration stood out. The source says the brightening lasted roughly 60 minutes, which is short enough that current surveys are only barely able to detect similar objects.
That same data set gave the team its strongest clue about what Phoebe might be. The source presents three possibilities: a free floating planet, a planet belonging to the Large Magellanic Cloud, or a primordial black hole.
Phoebe's Mass Estimate
The mass estimate pushes the object into a narrow range. The team's calculation placed Phoebe far below the roughly five times that of the Sun minimum mass for a stellar black hole, leaving only a much smaller black hole formed in the Big Bang itself within the source's explanation.
The source says Phoebe is five orders of magnitude more likely to be a dark matter object than anything associated with normal stellar matter, and the dark matter halo between and around the Milky Way and the Large Magellanic Cloud won by a factor of 100,000 in the team's probability calculation.
Large Magellanic Cloud Clue
For astronomers, the practical result is narrow but useful: a one-hour event from 18 December 2019 points to an object that is tiny by stellar standards and hard to catch in ongoing surveys. The star went back to normal and has not shown the same variation again, leaving Phoebe as the name attached to the lensing object in the record.
