Space Jam: Extragalactic planets

Rahul Rao

In the past week, astronomers announced that they have discovered the first known exoplanets located in another galaxy.

That much, while no doubt a milestone for exoplanet discoveries, should not come as any great surprise. It is patently obvious that exoplanets should exist in other galaxies, considering that many thousands have been discovered in our own galaxy, and there is virtually nothing differentiating other galaxies’ interiors from our own.

The impressive part of this discovery is its distance; the exoplanet in question is 3.8 billion light-years away. For comparison, the nearest galaxies to us are less than 100,000 light-years away, and the Andromeda galaxy, the nearest major galaxy of Milky Way-esque size, is 2.5 million light-years away. This exoplanet is over a thousand times that distance, and certainly many orders of magnitude further than any exoplanet discovered thus far.

Of course, 3.8 billion light-years is far too distant to observe directly. Instead, astronomers were able to discover these planets by using a technique called “quasar microlensing,” in which the light from a distant object (a quasar, in this case) is influenced by the gravitational field of smaller objects in the way, creating detectable spikes in the distant object’s light curve.

Astronomers managed to find as many as two thousand exoplanet candidates via this method, ranging from the mass of the Moon to the mass of Jupiter, a staggering amount and a range that encompasses virtually the full scale of possible planet sizes.

The planets are also unbound, or rogue planets– they are not orbiting any star. It is becoming increasingly clear that there are vast, vast numbers of such rogue planets, previously thought to be solely the realm of fiction. Other exoplanet detection methods, reliant on observing the light of stars, have a difficult time observing rogue planets.

Although these are merely candidates, and many of them may be false positives or otherwise remain unconfirmed, it is still unprecedented.

The holy grail of exoplanets, other Earth-like planets proven to hold life, remains tantalizingly elusive, despite an increasing list of candidates (many of which end up being overhyped by people in the media who do not know better). Still, this is an exciting development in exoplanet research– a field that is mere decades old, and continuing to make great discoveries.