On the night of December 18, 2019, something unusual happened in the Large Magellanic Cloud, a satellite galaxy of ours. A star briefly brightened, not with a bang, but in a gentle rise and fall of brightness over about an hour. This odd event has been named Phoebe, and figuring out its nature has become a fascinating challenge for astronomers.
This phenomenon is a result of gravitational microlensing, a concept rooted in Einstein’s general theory of relativity. When a massive object passes between us and a distant star, it acts like a lens, magnifying the star’s light in a unique way. This pattern is different from what variable stars, flares, or asteroids produce.
A team from Swinburne University in Melbourne spotted Phoebe during a survey. They quickly recognized it as a microlensing event, but the real mystery lies in what Phoebe actually is.
Three main theories exist about Phoebe. It could be:
- A free-floating planet, ejected from its solar system, now drifting alone.
- A similar planet from the Large Magellanic Cloud, which would be the first extragalactic microlensing planet found.
- A primordial black hole, which forms from density fluctuations shortly after the Big Bang.
The duration of this event is key. The mass of the object doing the lensing affects how long the brightening lasts. With a 60-minute duration, Phoebe’s mass is estimated to be about three times that of the Moon. This makes it far smaller than any known planet and too light to be any type of stellar black hole, which generally needs to be at least five times the mass of the Sun.
Experts believe Phoebe may be linked to dark matter. The researchers calculated that it is 100,000 times more likely to be a dark matter object than something related to normal stars. If true, Phoebe would be among the oldest objects detected, formed in the chaotic early universe—long before the first stars or atoms existed.
In a world where cosmic mysteries intrigue many, Phoebe reminds us of the universe’s vastness and history. The light it bent for just one hour tells a story of an object drifting through the cosmos for 13 billion years.
For more on this, you can check out the research here: AMPM II. A Lunar-Mass Primordial Black Hole Microlensing Candidate in the Milky Way Halo.
This discovery not only adds depth to our understanding of dark matter but also fuels curiosity about the universe’s hidden treasures.
